Cornell University computer program helps identify food-borne pathogens

Cornell University scientists have developed a computer program, Environmental Monitoring With an Agent-Based Model of listeria EnABLe, to simulate the most likely locations in processing facilities where the food-borne pathogen listeria monocytogenes might be found. Food-borne listeria infects about 1,600 people in the United States each year with about one in five of those infections ending in death.

Continue reading Cornell University computer program helps identify food-borne pathogens

Controlling basil downy mildew might be as simple as turning on a light

The use of supplemental light to control downy mildew on food and ornamental crops could be integrated into current disease management practices.

Downy mildew is a major disease on both ornamental and food crops. Whether these crops are grown outdoors or in a controlled environment, environmental conditions, generally cool to moderate temperatures and high humidity, are favorable to downy mildew development. Warm temperatures and high humidity are conducive to powdery mildew development.

Continue reading Controlling basil downy mildew might be as simple as turning on a light

Hort Americas looks to be a connector of products and knowledge for the horticulture industry

Whether growers are producing vegetables, ornamentals or other hydroponic crops, Hort Americas is working to provide its customers with the products and knowledge they need to be successful.

When Hort Americas in Bedford, Texas, started operating as a wholesale horticulture distributor in March 2009, the company had no existing customer base.

Continue reading Hort Americas looks to be a connector of products and knowledge for the horticulture industry

GLASE consortium aims to improve greenhouse energy efficiency

Even though the Greenhouse Lighting and Systems Engineering (GLASE) consortium is New York-based, the research it is doing has the potential to impact controlled environment agriculture worldwide.

The Greenhouse Lighting and Systems Engineering (GLASE) consortium is a partnership between Cornell University in Ithaca, N.Y., and Rensselaer Polytechnic Institute (RPI) in Albany, N.Y. The consortium will be conducting research to improve controlled environment agriculture (CEA) operations including reducing energy consumption.



The goal of the consortium is to create a more sustainable and profitable greenhouse industry. Although the focus of the research will be on greenhouse production, the findings should also have application to indoor CEA production including vertical farms and warehouses. Greenhouses, which can be electricity-intensive depending on the level of automation, cover 720 acres in New York State. The consortium is looking to reduce greenhouse electricity use and concomitant carbon emission by 70 percent and to increase crop yields by 2030.

Erico Mattos, who was appointed executive director of GLASE in June, said he has been hired as a subcontractor by Cornell University and will be working to recruit industry members to join the consortium.

“Currently I have a 50 percent time appointment with GLASE,” Mattos said. “My time with GLASE will increase as we bring in industry members. I am living in Georgia, but will be moving to upstate New York over the next year and will be located between RPI in Albany and Cornell University in Ithaca.”

Mattos said GLASE is a seven-year project which has received $5 million from the New York State Energy Research and Development Authority (NYSERDA). The money will be used to sponsor research between Cornell and RPI.

“The team leaders who will be doing the research are Neil Mattson at Cornell University and Tessa Pocock at RPI,” said Mattos. “They have a set of more than 300 milestones that their teams have to reach. They have already achieved some of these milestones.”

The research activities include improving lighting fixtures and systems that synergistically control lighting, ventilation, humidity and carbon dioxide, improving CEA operations and reducing energy consumption to create a more sustainable and profitable greenhouse industry.

“The teams at Cornell and RPI are well equipped with the resources they need to achieve the milestones of the core research proposal that has been sponsored by NYSERDA,” he said. “Even though the teams led by Neil and Tessa are completely self-sustainable, they may require some outside partnerships to achieve some of the goals.”

The GLASE consortium is headed by researchers Tessa Pocock at Rensselaer Polytechnic Institute and Neil Mattson at Cornell University and GLASE executive director Erico Mattos.
Photo courtesy of GLASE

Mattos said in his role as executive director he will act as an intermediary between Cornell, RPI and NYSERDA making sure that the research is proceeding and that milestones are being completed on time.

“The most important part of my position is to create a consortium with industry members,” Mattos said. “The goal over the next seven years will be for the project to receive less money from NYSERDA and more money from industry members. We want to establish a consortium that is self-sustaining. By bringing in industry members we will have money to do our own-sponsored research, technology transfer, outreach, and market research, all these types of things and GLASE will be self-financing.

“My role as executive director is to ensure that the team moves in this direction. By bringing in industry members, offering them the project and making sure that we provide them with access to the technology that is developed by Cornell and RPI.”


Complementary research

Mattos said the research that will be done at Cornell and RPI is complementary and will not overlap.

“RPI will be doing more engineering-related research, such as looking at light fixtures and components including the drivers and controllers,” he said. “They are also looking at photobiology—how plants respond to different spectra as they grow and produce different nutritional compounds and changes in plant metabolism and morphology. The RPI research work is more engineering-related.

“The research at Cornell is going to be more applied in the greenhouse, such as interactions of carbon dioxide enrichment and lighting control studies. Cornell will implement some of the systems that have already been developed at Cornell. Cornell will also be looking at different systems and different crops. Initially the studies will be done with tomatoes, lettuce and strawberries and then will be extended as necessary.”


The research conducted at Cornell University will be more applied in the greenhouse, including carbon dioxide enrichment and lighting control studies.
Photo by Chris Kitchen, Cornel Univ. Marketing

Mattos said the research will be expanded to commercial size greenhouses in New York, which will be 6,000 square feet for a small scale greenhouse and 20,000 square feet for a large scale greenhouse.

“RPI will develop new systems and Cornell will implement the greenhouse tests and then move forward to a final demonstration,” he said.

Mattos said the researchers will also be working in partnership with A.J. Both at Rutgers University, who will be doing some of the energy efficacy and radiometric studies of the light fixtures.

“One of the milestones Cornell research associate Kale Harbick will be working on is modeling,” Mattos said. “This will involve trying to calculate in advance how much energy in a greenhouse is consumed and what happens if some of the variables are changed. The research will look at how these changes affect the general energy consumption of the greenhouse.”


Seeking industry support

Mattos said when GLASE was developed over 30 industry companies provided letters of support indicating they wanted to become part of the consortium as industry members. Since the consortium was started, many other companies have expressed their interest in becoming part of the consortium.

“Even though these companies signed letters of support that doesn’t mean they will all become consortium members,” he said. “Cornell and RPI are both already working in partnership with some companies to develop the core research. There is nothing official as industry members yet. We are looking to bring in other industry members and really make them a part of this consortium. We want to reach a broad range of industry members so this support could be both financial or it could be providing equipment to conduct the research. But the primary goal is to bring in financial support.”

Mattos said there will be a series of benefits that come with industry membership.

“They would pay for a membership and then they would get a series of benefits. We are now working with a marketing media company to promote the consortium and the opportunity for membership.

“We want to bring in large manufacturing companies, but we also want to address the other end of the spectrum and work with small growers. The growers will benefit the most from this research.”


Academic collaborators, information hub

Mattos said it is the intension of the consortium to expand with researchers from outside New York.

“We intend to establish future academic collaborations to develop new research projects partially funded by GLASE through industry membership funds and new research grants,” he said.

Another goal of GLASE is to create a hub for greenhouse lighting and systems engineering which includes the centralization of information.

“We will create a central database to indicate the academic research currently on-going in the U.S. (what, where and who) to facilitate the interaction between the industry and academia,” he said.


Impact on greenhouse, plant systems

The crops that are to be studied initially by Cornell and RPI researchers are tomatoes, lettuce and strawberries.

“These are commercially relevant crops,” Mattos said “I went to Ithaca and met some of the members of Neil’s team, including graduate students Jonathan Allred and Erica Hernandez and research technician Matthew Moghaddam, who have been working with tomatoes and strawberries. Lettuce is also one of the most commonly produced greenhouse crops.

“Part of the milestones that Tessa will be working on will be done in environmentally controlled growth chambers and growth rooms. Tessa does not have a greenhouse. Most of the research that she will be doing is related to photobiology. Everything that she will be doing has application to warehouse production even though she is not doing the research in a warehouse. This research will look at nutritional compounds and pigment production. The research in the growth chambers will be compared with greenhouse studies.”

The research conducted at RPI will be done in growth chambers and growth rooms, which should have application to commercial warehouse production.
Photo courtesy of GLASE

Although the RPI research is not targeted for commercial indoor farms, Mattos said the results could be used to support that type of production.

“The proposal is to reduce greenhouse crop production energy consumption by 70 percent in seven years,” he said. “The economic factor and the majority of the research will be looking at greenhouse systems and how to integrate them. Economically we are focused on greenhouses. But we will be doing studies in growth chambers that may have application to support indoor farm production.

“Tessa will be looking especially at biological efficacy. Everybody talks about the efficacy of the light fixtures themselves. A lot of people are looking at that. Getting less attention is the biological efficacy, which is if there is a different spectrum, the same amount of photons or micromoles, can have a different impact on plants. Not only the morphology, but also the pigments, the chemical pathways. This is the biological efficacy.”


For more: Erico Mattos, Greenhouse Lighting and Systems Engineering (GLASE) consortium; (302) 290-1560;;


David Kuack is a freelance technical writer in Fort Worth, Texas;

Looking for a better, easier way to do greenhouse IPM?

Greenhouse Scout is an integrated pest management app that makes it easier to collect, store and analyze scouting data along with identifying insect pests and which beneficials can be used to control them.

Most greenhouse growers know the benefits of scouting their crops for pest insects and mites. Scouting can help to identify and minimize pest outbreaks, reduce plant damage and crop losses and save on pesticide and biological control costs.

Continue reading Looking for a better, easier way to do greenhouse IPM?

Fertilizer trials look at leafy greens, herb growth in hydroponic production systems

Early results from fertilizer trials in Hort Americas’ research greenhouse show knowing the levels of nutrients in fertilizer solutions can go a long way in avoiding problems with deficiencies and toxicities.

Hort Americas has retrofitted a 12,000-square-foot greenhouse in Dallas, Texas, for the purpose of studying edible crop production in a variety of hydroponic production systems. The greenhouse is also being used to demonstrate products offered in the company’s online catalog.

Tyler Baras, who is the company’s special projects manager, is overseeing the trialing of leafy greens and herbs in five different production systems.

“We’ve got a deep water culture or raft system using Hort Americas’ fertilizer blend with calcium nitrate and magnesium sulfate,” Baras said. “We are using that same nutrient mix in a nutrient film technique (NFT) system and a capillary mat system.

“I’m using Terra Genesis organic fertilizer in a vertical grow tower. I’m also using the same organic fertilizer for all of the seedling propagation in a flood-and-drain vertical rack.”

Tyler Baras, special projects manager at Hort Americas, is overseeing the trialing of leafy greens and herbs in different production systems, including deep water culture and nutrient film technique. Photos courtesy of Tyler Baras, Hort Americas
Tyler Baras, special projects manager at Hort Americas, is overseeing the trialing of leafy greens and herbs in different production systems, including deep water culture and nutrient film technique.
Photos courtesy of Tyler Baras, Hort Americas

Baras said the fertilizer recipe he is using in the deep water culture and NFT systems is based on general recommendations from Cornell University and the University of Arizona for leafy greens crop production.

Differences in nutrient levels

The deep water culture system has been running for three months. The water reservoir for the system is 8,000 gallons.

“Even if water evaporates, since it is such a large body of water, the electrical conductivity (EC) doesn’t really move much,” Baras said. “The EC has been very stable during the three months it has been operating. The reading has barely moved.”

The first trial with the NFT system, which has a reservoir of about 140 gallons, lasted for three months.

“Every week I added an additional 40 gallons of water on average to the NFT reservoir,” Baras said. “The water is evaporating and the salts are accumulating a lot faster in the NFT reservoir than in the deep water culture system. Because the NFT system has a smaller water reservoir, the quicker evaporation rate and the water replacement in the reservoir, has caused the EC to shift a lot more.”

One of the goals of the fertilizer trials is to see what salts are accumulating in the NFT system and to see how long the system can run before it has to be flushed.
One of the goals of the fertilizer trials is to see what salts are accumulating in the NFT system and to see how long the system can run before it has to be flushed.

Baras said even with the changes in nutrient levels all of the plants have been performing well.

“I haven’t seen any nutrient deficiencies or toxicities even as the fertilizer recipe has shifted over time. We have been trialing a wide range of crops, including butterhead and romaine lettuces, kale, spring mixes and basil. I’m trialing a lot of crops to figure out when these crops start to be impacted by possibly too much salt accumulation. I haven’t seen anything yet that is alarming.

“One of the things that I have seen over the years working with fertilizers is how wide the acceptable range is for plants to grow well. Between the NFT and deep water culture, the NFT is using half the nitrogen and the plants are performing very similarly. There are recommendations for EC, but none of these fertilizer levels are set. I have some systems that have 20 parts per million phosphorus and some that have 50 ppm and the plants look the same. Most general recommendations say 40-50 ppm. I’ll have some solutions that have 3 ppm iron and others that have 6 ppm iron. It is interesting to see how wide the range is for a lot of these nutrients and the crops are performing the same.”

During the three months that the deep water culture system has been running the electrical conductivity (EC) has been very stable with plants showing no signs of nutrient deficiencies or toxicities.
During the three months that the deep water culture system has been running the electrical conductivity (EC) has been very stable with plants showing no signs of nutrient deficiencies or toxicities.

Baras said he has seen a slowing of plant growth in the NFT system.

“I’m not seeing any deficiencies or toxicities, but the crops have slowed down about a week over the deep water culture,” he said. “Depending on the crop, it’s taking a week longer to reach either the plants’ salable weight or height.

“The slowing in growth could be related to the nutrients. This could be useful information for growers. If they are checking the EC, which may have been 2.3 when a crop was started, if there is a slowing of growth, growers may want to have a water test done. The test could show that the amount of nutrients might be changing.”

Identifying what makes up the EC

During the three months that Baras had been running the NFT system he never flushed the system.

“All that I’ve done with the NFT system is add water and additional fertilizer to maintain a targeted EC,” he said. “One of the goals of the trials is to see what ions are accumulating in the system and to see how long I can run the system before it has to be flushed. When I started the target EC was 2.2-2.3. I still achieved the target EC at three months, but the composition of what was actually in the water changed.

“Originally the NFT fertilizer solution contained about 185 parts per million nitrogen. At the end of the trial the EC was the same but there was only 108 ppm nitrogen in the solution. The calcium concentration was originally 250 ppm and ended at 338 ppm. Sulphur was originally at 80 ppm and rose to 250 ppm. Nutrients have accumulated as the water evaporated. Solely going by the EC meter reading doesn’t tell the full story of what is in that water. The EC of the fertilizer solution that I started with is the same as the EC for the fertilizer solution three months later. The difference is the ions that are making up that ending EC.”

Herb production with organic fertilizer

Baras is growing a variety of cut herbs in vertical grow towers. The plants are fertilized with Terra Genesis, a molasses-based organic fertilizer. He said Hort Americas has been hearing from tower growers who are interested in trying to grow organically.

“What we are seeing is the organic fertilizer solution can change a lot over time,” he said. “The fertilizer tank solution matures as time goes on. With the organic fertilizer, the nutrients tend to balance out as the solution is run longer.

“Our city water contains calcium and some magnesium. These elements are actually the nutrients that the organic fertilizer is slightly low in. So as I run the system longer, through the addition of city water, I actually start to see an accumulation of both calcium and magnesium, which actually helps balance out the total fertilizer recipe. The balance of the nutrients has improved over time.

A variety of cut herbs are being grown in vertical grow towers and fertilized with Terra Genesis, a molasses-based organic fertilizer.
A variety of cut herbs are being grown in vertical grow towers and fertilized with Terra Genesis, a molasses-based organic fertilizer.

The pH was fairly unstable as it seemed to be going through several biological waves. It was moving rapidly between high and low. As I run the tank solution longer the total alkalinity has increased, which has stabilized it. The biological activity has also started to stabilize. The pH has stabilized in the upper 5 range. For the plants grown organically I have seen deficiencies pop up. The deficiencies were reduced as the fertilizer tank solution ran longer. The deficiencies appear to have balanced out.”

Baras said one noticeable difference between the NFT, deep water and vertical grow towers is how much slower the plants grow in the towers.

“I don’t know what to contribute the slower growth to yet,” he said. “It could be trying to determine the best fertilizer rate for the fertilizer. It could be the crop selection, because most of the crops in the towers are different from what I’m growing in the NFT and deep water culture.

“I’m going to start a deep water culture and NFT trial using organic fertilizer. I’ll have three different organic production systems running simultaneously so I will be able to compare the plant growth in each system. I’ll also be able to compare the growth of the same crops grown with organic or conventional fertilizers.”

Controlling biofilm, disease pathogens

Baras said one of the issues that can arise with using organic fertilizer is the development of biofilm in the irrigation lines that can cause emitters to clog.

“I am incorporating a product called TerraBella, which contains beneficial microbes,” he said. “These microbes help mobilize certain nutrients, like phosphorus, which can promote the formation of biofilms. This biofilm buildup is usually more of a problem with high water temperatures.

“About every six weeks I add a booster application of the beneficial microbes depending on the production system. The deep water culture system has a larger reservoir so I am not replacing evaporated water as often. For the other productions systems, like the NFT and grow towers, where I am replacing the water, I am incorporating the beneficials more often. For these systems, the fresh city water that is added dilutes the fertilizer solution. Also, there is chlorine in the city water that possibly could negatively impact some of the beneficial microbes.

For more: Hort Americas, (469) 532-2383;

David Kuack is a freelance technical writer in Fort Worth, Texas;


Products being used in greenhouse trials



Monitoring is crucial for growing lettuce and leafy greens year round

Since lettuce and leafy greens have short production cycles, greenhouse growers need to stay focused if they want to be successful growing these crops year round.

The increasing demand for locally-grown vegetables is causing more field vegetable growers, ornamental plant growers and new growers to look at trying to satisfy this market. Cornell University horticulture professor Neil Mattson said he works with all three types of growers.

“I see both vegetable field growers and ornamental greenhouse growers trying to produce lettuce and leafy greens year round,” he said. “Both are quite common. Field vegetable growers are looking for a crop that can generate year-round cash flow. Ornamental growers are looking to fill their greenhouses in the off-season. A lot of ornamental growers no longer produce poinsettias in the fall or spring bulb crops and spring plant propagation that they would normally do in the winter. Growers could have as much as a six-month window when their facilities are not being used.”

Mattson said ornamental growers tend to better understand what it takes to grow a year-round crop.

“Ornamental growers tend to be aware of differences in crops and the problems that can arise,” he said. “They also understand the concept that there is much less light in the winter so they may have to consider using supplemental light. Ornamental growers are usually aware of the high cost of heating a greenhouse year round, especially during the winter.

“In general, field vegetable growers who have greenhouses, may only be using those structures in the spring to produce their transplants. That means they may be used to heating a couple months each year.”


Controlling environmental parameters

During this year’s Cultivate’16 conference and trade show in Columbus, Ohio, Mattson did a presentation on the year-round production of leafy greens using controlled environment agriculture (CEA). The main environmental conditions growers need to monitor and control include light, temperature and relative humidity.



Mattson said in the northern half of the United States light availability during the winter months is the most difficult environmental issue to deal with when growing plants year round.

“The target light level for lettuce production is 17 moles of light per square meter per day (daily light integral, mol/m2/d) for optimal growth,” he said. “In most parts of the country achieving that target usually isn’t an issue during the summer. In the winter, in the northern part of the country, light levels can be 5 mol/m2/d on average and even 1-3 mol/m2/d is common. That is three to five times less light than what is needed for optimum lettuce growth during the winter.”


Photo 1, Lettuce overview 1, Neil Mattson, Cornell Univ.
The target light level for lettuce production is 17 moles of light per square meter per day (daily light integral) for optimal growth.
Photos courtesy of Neil Mattson, Cornell Univ.


Mattson said supplemental light, using LEDs or high pressure sodium lamps (See the Lamps Needed Calculator, can be provided to deliver higher light levels to increase lettuce biomass. But going above 17 mol/m2/d can cause growers to have issues with tip burn.

“In the case of head lettuce, a grower can go from seed to harvested head (5-6 ounces) in 35 days if there is 17 mol/m2/d. If there is only 8.5 mol/m2/d, it takes the plants twice as long to produce that same biomass.

“For baby leaf greens, if they are seeded and transplanted and grown on for two weeks before harvesting and only receive 8.5 moles of light, the plants will only produce half the yield. If a grower normally harvests 10 ounces per square foot and there is only half the light, the plants will produce only 5 ounces per square foot.”

Mattson said a rule of thumb for New York is a grower can light a 1-acre greenhouse and produce the same yields as not lighting a 3-acre greenhouse to produce the same yields during the winter months.



Lettuce and many other leafy greens are cold tolerant. Mattson said a lot of growers want to grow them cold.

“The Cornell CEA research group proposes that these crops be grown at fairly warm temperatures so that they have the faster 35-day crop cycle,” he said. “This is based on having 17 mol/m2/d and a daily average temperature of 70ºF-75ºF during the day and 65ºF at night.

“During the winter the issue with temperature is paying to heat the greenhouse. It’s easy to control the temperature, growers just have to be willing to crank up the thermostat.”

Mattson said temperature can be really hard to control in southern climates in the U.S.

“Under hot conditions, temperatures in the 80s and 90s, head lettuce is going to bolt prematurely,” he said. “It can be difficult to drop the day temperature low enough to avoid early bolting.”

Beyond trying to reduce the air temperature, research done by the Cornell CEA group has shown that lowering the root zone temperature to 74ºF or less using chilled water can help prevent premature bolting.

“Chilling the root zone temperature allows growers to grow using warmer air temperatures by having the cooler water temperature,” Mattson said. “This is an effective way to chill the plants even when the air temperatures reach the 80s and 90s.”

Mattson said the biggest issue with warmer air temperatures occurs with lettuce and spinach. Warmer temperature and long day conditions can both cause spinach to experience premature bolting. Mattson said warmer temperatures can also promote Pythium root rot on spinach. Spinach is much more susceptible to this water mold than lettuce or other leafy greens.

“Chilling the root zone temperature can help to prevent the disease organism from developing as quickly as at warmer temperatures,” Mattson said. “If the root zone temperature can be kept cool, it won’t completely avoid the Pythium issue, but it will help control it.”


Pythium baby leaf spinach, Neil Mattson, Cornell Univ.
Cooling the root zone temperature won’t completely avoid Pythium disease, but it will help control it.


Pythium spinach closeup, Neil Mattson, Cornell Univ.
Close-up view showing Pythium root rot on spinach.


The Cornell CEA group found that the optimum root zone temperature for spinach was 64ºF-65ºF. At this temperature Pythium was deterred, but there was no crop delay. If the root zone temperature is lowered to 62ºF, plant growth is slowed.


Relative humidity

Mattson said the relative humidity for lettuce and leafy greens should be between 50-70 percent. He said the lower humidity helps to limit pathogen issues.

“High humidity favors powdery mildew and Botrytis,” he said. “High humidity also favors the physiological disorder tip burn. Tip burn is caused by a calcium deficiency. The higher the relative humidity the less transpiration occurs in the plant resulting in the plant not taking up an adequate amount of calcium.”


Lettuce tipburn, Neil Mattson, Cornell Univ.
High humidity favors the physiological disorder tip burn, which is caused by a calcium deficiency.


Mattson said a relative humidity lower than 50 percent can cause an outer leaf edge burn, which is a physiological disorder.

“This is a different disorder than tip burn caused by calcium deficiency,” Mattson said. “The outer leaves develop lesions where the veins end on the edge of the leaves. The lesions occur where the sap exudes out of the veins and then is reabsorbed by the plant and there is a kind of salt buildup.”


Fertilization, water quality

Although fertilization and water quality are not environmental parameters, growers can have issues with both if they don’t monitor them. Lettuce and leafy greens are not particularly heavy feeders compared to other greenhouse vegetables like tomatoes and other vine crops. Mattson said lettuce and leafy greens are relatively forgiving crops when it comes to fertilization.

“Growers need to monitor the nutrient solution every day in regards to pH and electrical conductivity (EC),” he said. “The reason for testing the nutrient solution at least daily is because in hydroponics the nutrient solution pH can change by one or two units in a day.”

Mattson said for container crops like petunia and geranium, pH does not usually change by more than one unit in a week. He said container growers may check the pH every week, and some may only do it every two weeks. But for hydroponics a grower needs to stay on top of changes in pH.

In addition to daily pH and EC monitoring, Mattson said a detailed elemental analysis of the nutrient solution is important.

“Periodically, about every four weeks, growers should send a sample of their nutrient solution to a testing lab to determine if the plants are absorbing nutrients in the proportions the growers expect,” he said. “Certain elements in the solution may decline over time and a grower may have to add more of these elements and less of others.”

Mattson said some systems, like CropKing’s Fertroller, have automated sensors which measure pH and EC in line so it’s a real time measurement. The controller makes the necessary adjustments.

“Typically if a grower is putting high alkalinity water into the system, the pH tends to creep up over time, so the controller automatically adds acid to reach a target pH,” he said. “Likewise, the machine does that with EC too. If the EC is going down because the plants are taking up nutrients, the controller adds fertilizer stock solution to reach a target EC.”

Mattson said iron deficiency due to high pH is the most common nutrient disorder he sees on lettuce and leafy greens. Occasionally magnesium deficiency occurs because the water source contains enough calcium, but not enough magnesium.


Iron deficiency due to high pH is usually the most common nutrient disorder on lettuce and leafy greens.


“Many fertilizers don’t include calcium and magnesium, so growers can run into issues with magnesium deficiency,” he said. “Basil tends to have a high need for magnesium. We usually recommend basil be provided twice as much magnesium as lettuce.”


Photo 6, Basil magnesium deficiency, Neil Mattson, Cornell Univ.
Basil tends to have a high need for magnesium and usually should receive twice as much magnesium as lettuce.


Mattson said growers should test their water more frequently to determine if there have been any changes in the alkalinity of the water, including calcium, magnesium and sodium concentrations.

“In the Northeast this summer, we are experiencing a drought,” he said. “I’ve heard from growers who say the EC of their water is going up, which implies that some salt levels are going up. But we don’t know specifically which salts and that would be useful to know what specifically is changing.

“It really depends on their water quality. In particular, EC, alkalinity and whether there are any nutrients in high concentrations, like sodium, can be an issue. It really comes down to how long they are trying to capture and reuse the water. In our Cornell system we have traditionally grown in floating ponds. We use that same water cycle after cycle for several years. We can continually use the same water because we start with deionized water. However, even if the water has fairly low salt levels, using the same water will result in the accumulation of sodium to harmful levels over time.”


For more:
Neil Mattson, Cornell University
School of Integrative Plant Science, Horticulture Section
49D Plant Science
Ithaca, NY 14853
(607) 255-0621

Cornell Controlled Environment Agriculture “Hydroponic Lettuce Handbook”


David Kuack is a freelance technical writer in Fort Worth, Texas;


Webinar on “Managing Nutrient Solutions for Hydroponic Leafy Greens and Herbs”

If you missed the e-GRO webinar “Managing Nutrient Solutions for Hydroponic Leafy Greens and Herbs” on Jan. 22, 2016, which was sponsored by Hort Americas, you can still view the webinar on YouTube.

Hydroponic greens and herbs are produced in systems with recirculating nutrient solutions. In order to maintain productive and quality crops, it is important to know how to properly maintain the nutrient solutions. Dr. Chris Currey at Iowa State University and Dr. Neil Mattson at Cornell University discuss strategies for managing pH and EC, formulating nutrient solutions and identifying common nutrient disorders.

Part 1: Common production systems, pH and EC management

Presented by Dr. Chris Currey, Iowa State University


Part 2: Nutrient solution recipes, common nutrient disorders

Present by Dr. Neil Mattson, Cornell University

Maintaining the optimum temperature, oxygen and beneficial microbe levels are integral in hydroponic systems

Hydroponic floating raft lettuce

While providing the proper soluble salts and pH levels are important in hydroponic systems, don’t overlook the significance of maintaining the optimum temperature, oxygen concentration and microbe level in the nutrient solution.

Maintaining the proper soluble salts (electrical conductivity) level and pH are critical in hydroponic systems like nutrient film technique and floating rafts. While monitoring these properties are important, growers should not overlook the importance that temperature, oxygen level and microbial activity play in the growth of plants in these production systems.

“It’s not as much about maintaining root health as it is about managing the conditions in the rhizosphere, which is the region around the plant roots,” said Rosa Raudales, assistant professor of horticulture and greenhouse extension specialist at the University of Connecticut. “The area around the roots undergoes a lot of biological and chemical activity. Microorganisms in the rhizosphere feed on the exudate of the roots. Managing the rhizosphere and the conditions in the nutrient solution are critical to maintaining plant health.”


Hydroponic root system health, Rosa Raudales, Univ. of Conn.
Factors that can impact root health in hydroponic systems include soluble salts, pH, temperature, oxygen level and beneficial microbial activity.
Photo courtesy of Rosa Raudales, Univ. of Conn.



Maintain optimum root temperatures

While providing the proper air temperature in a greenhouse or controlled environment agriculture system is important, maintaining the optimum root temperature can have a bigger impact on the health and production time of a crop.

“If higher temperatures are maintained in the root zone then the plants are going to lose a lot of energy,” Raudales said. “Temperatures above the optimum in the root zone affect the cell membrane integrity of the roots. A disruption of the cell membranes affects the function of the roots resulting in less nutrient uptake, which affects crop cycles and yields.

“If plants are grown at root temperatures lower than the optimum, the plants grow slower because their metabolism is slower. In the worst case scenario, if freezing temperatures occur then ice crystals could form in the cells resulting in cell leakage and cell disruption.”

Cornell University researchers have conducted studies ( to identify the specific temperatures that are ideal for hydroponically-grown vegetables.

“Cornell researchers found the temperature of the nutrient solution had a greater effect than the air temperature,” Raudales said. “Lettuce plants exposed to air temperatures ranging between17ºC (62.6ºF) and 31ºC (87.8ºF) had consistent yields as long as the nutrient solution had a consistent temperature of 24ºC (75.2ºF). This research was done in the 1990s, but it still has application today.

“Cornell researchers did a similar study with spinach and they found the optimum root temperature was 22ºC (72ºF). They tested air temperatures ranging from 16ºC to 33ºC (60.8ºF-91.4ºF) and they found as long as the root temperature was 22ºC, the air temperature could be in that range and plants still produced optimum yields. For tomatoes the optimum root temperature is 25ºC (77ºF).”

Raudales said growers who are producing hydroponic leafy greens like lettuce and spinach have the option of installing a water heater to maintain the optimum root temperatures.

“It is easier and less expensive to heat the nutrient solution than to keep the whole greenhouse warm,” she said. “Heating the greenhouse does not make economic sense, when the research indicates that the temperature of the nutrient solution is a more important factor. If a grower is producing lettuce and spinach, which can tolerate lower air temperatures, it makes sense to run the greenhouses cooler and to install a water heater to adjust the nutrient solution temperature.”

Maintain adequate oxygen levels

Raudales said the dissolved oxygen level in a hydroponic solution needs to be maintained so respiration can occur in the roots.

“When oxygen levels are low in the root zone, the roots do not take up the nutrients required for growth,” she said. “Low oxygen levels cause increased ethylene production in the roots. If there are higher ethylene levels in the roots then the roots start to mature and die. The more oxygen present, the better the nutrient uptake and the better the root system.”

Raudales said there is also an inverse relationship between the oxygen level and solution temperature.

“If the root zone temperature is high, then the oxygen level is going to go down,” she said. “This is another reason why the root zone temperature is so important. The optimum oxygen level should be greater or equal to 6 parts per million of dissolved oxygen in the root zone. Plants should be able to handle 6-10 ppm without any problems.”

Raudales said growers who are using nutrient film technique systems typically don’t need to do any type of aeration. The movement caused by the flow of the water is usually enough to keep the oxygen level high enough in the solution.

Raudales said growers who are using floating rafts usually incorporate some type of oxygen-generating system.

“There are different ways of oxygenating the water,” she said. “One is aerating the water where air is being pumped into the water. Air is not pure oxygen, but it contains enough oxygen for what is needed in the hydroponic solution.”


Hydroponic floating raft lettuce
Growers who are using floating rafts usually incorporate some type of oxygen-generating system to ensure the oxygen level is 6 parts per million or higher.



Raudales said another reason for maintaining a high oxygen level in the hydroponic solution is the effect it can have on pathogenic fungal zoospores.

“If there is more oxygen, then zoospores don’t survive as well,” she said. “Zoospores don’t want completely anaerobic conditions, but they do better in conditions where there is less oxygen.

Pathogens of concern include Phytophthora, Pythium, Thielaviopsis basicola and Xanthomonas.

“Growers should try to keep the oxygen level high. If there are warmer temperatures, then there are lower oxygen levels. When there are lower oxygen levels the plants are not as healthy and more zoospores tend to survive. This is one of the reasons why there tends to be more disease issues during the summer than during the winter.”

Raudales said growers who are using floating rafts should be measuring the oxygen level regularly. Meters for measuring dissolved oxygen look like pH meters and are simple to operate.

Maintain beneficial microbes

Raudales said beneficial microbes are present naturally in water. Commercial products with beneficial microbes can also be incorporated into the hydroponic solution.

“Growers who are using the floating rafts tend to treat the nutrient solution like gold,” she said.

“They don’t want to replace it because they have a solution which is very high in beneficial microbes. Growers can inoculate the nutrient solution with a commercial biocontrol product or they can allow the good microbes to build up with time.

“As long as growers maintain the other parameters at optimum levels, including root temperature, pH, nutrients and oxygen levels, there typically isn’t a problem with diseases. This is very comparable to what happens with plants grown in substrates. The microbes build up naturally in the water just like in a substrate. These microbes feed on the exudates of the roots.

They need carbon sources that they wouldn’t get just from the nutrient solution. The system has to be clean, but it doesn’t have to be clean to the point of having to start with a fresh solution every time a new crop is planted.”

For more: Rosa Raudales, University of Connecticut, Department of Plant Science and Landscape Architecture; (860) 486-6043;;

David Kuack is a freelance technical writer in Fort Worth, Texas;

Food Safety Modernization Act could impact growers exempt from the new federal rules

Food Safety Modernization Act

Although greenhouse and controlled environment agriculture growers may be exempt from implementing Food Safety Modernization Act rules, produce buyers may make compliance mandatory.

U.S. Centers for Disease Control and Prevention estimates 48 million people are sickened each year by foodborne pathogens. Of those people about 128,000 are hospitalized and 3,000 die each year.

On Nov. 13, 2015, U.S. Food and Drug Administration finalized three rules of the Food Safety Modernization Act. The purpose of FSMA, according to a FDA press release is to prevent foodborne illness “that, for the first time, establish enforceable safety standards for produce farms and makes importers accountable for verifying that imported food meets U.S. safety standards.” FDA said FSMA’s “final rules will help produce farmers and food importers take steps to prevent problems before they occur.”

“The recent multistate outbreak of Salmonella in imported cucumbers that has killed four Americans, hospitalized 157 and sickened hundreds more, is exactly the kind of outbreak these rules can help prevent,” said Michael Taylor, FDA deputy commissioner for foods and veterinary medicine. “The FDA is working with partners across the government and industry to prevent foodborne outbreaks. The rules will help better protect consumers from foodborne illness and strengthen their confidence that modern preventive practices are in place, no matter where in the world the food is produced.”

The three final rules released by FDA in November are the Produce Safety rule, the Foreign Supplier Verification Programs rule and the Accredited Third-Party Certification rule. FDA has finalized five of the seven major rules that implement the core of FSMA. In September 2015, FDA released the Preventive Controls for Human Food rule, which mandates preventive practices in food processing and storage facilities.

Produce Safety rule

The Produce Safety rule is the one rule that should have the biggest impact on outdoor farmers, greenhouse growers and controlled environment agriculture (CEA) growers. FDA used public comments and input collected during farm visits, meetings and listening sessions to develop a rule it says aims at reducing contamination risk while providing flexibility for farmers and growers.

This rule “establishes science-based standards for growing, harvesting, packing and holding produce that are designed to work effectively for food safety across the wide diversity of produce farms.” The rule’s standards include “requirements for water quality, employee health and hygiene, wild and domesticated animals, biological soil amendments of animal origin such as compost and manure, equipment, tools and buildings.” The rule’s standards have been designed to “help minimize the risk of serious illness or death from consumption of contaminated produce.”

The Food Safety Modernization Act’s Produce Safety rule includes standards for water quality, employee health and hygiene, equipment, tools and buildings.
The Food Safety Modernization Act’s Produce Safety rule includes standards for water quality, employee health and hygiene, equipment, tools and buildings.


One crop that the rule specifically addresses is the production of sprouts, which have been frequently associated with illness outbreaks. FDA reports that between 1996 and 2014, there were 43 outbreaks, 2,405 illnesses, 171 hospitalizations and three deaths associated with sprouts. Among the outbreaks was the first documented case of Listeria monocytogenes associated with sprouts in the United States. This crop is particularly vulnerable to microbial contamination because of the warm, moist conditions in which they are produced.

Exemptions to the Produce Safety rule

The earliest compliance date for the Produce Safety rule for some farms is two year after the effective date of the final rule. There are exemptions to the rule for some producers. These include farms that have an average annual value of produce sold during the previous three-year period of $25,000 or less. Also to be eligible for a qualified exemption, the farm must meet two requirements:

1. The farm must have food sales averaging less than $500,000 per year during the previous three years.

2. The farm’s sales to qualified end-users must exceed sales to all others combined during the previous three years. A qualified end-user is either (a) the consumer of the food or (b) a restaurant or retail food establishment that is located in the same state or the same Indian reservation as the farm or not more than 275 miles away.

Buyers driving food safety regulations

Dr. Elizabeth Bihn, director of the Produce Safety Alliance at Cornell University, said prior to FSMA, buyer demand has been the primary driver for implementation of food safety practices. “Consumers are buyers, but they are not protecting a name brand like Kroger or Wegmans or Wal-Mart,” Bihn said. “These companies are protecting their brands. They are going to have much higher stipulations for food safety then the consumers at farmers markets. There is some consumer demand for increased accountability for food safety, but it’s not as big a driver as the retail buyers’ demand. This includes most large food retailers.”

Food Safety Modernization Act
Even if greenhouse and controlled environment agriculture growers of food crops are exempt from the Food Safety Modernization Act, they may be pressured by buyers to adhere to the Act’s rules.

Bihn said greenhouse vegetable growers and CEA growers may receive added pressure from buyers to follow FSMA whether or not they are exempt from it.

“If a buyer tells a grower, “I’m not buying your produce unless you have a third party audit,” and the grower wants that company’s account, then the grower is going to do the audit,” Bihn said. “Legally a grower may be exempt from the regulation, but a buyer may say it doesn’t matter, the grower will still have to meet the regulation. There are still going to be markets that don’t require growers to meet the regulation if their operations are exempt from it. If you are a greenhouse grower who sells to a market that’s not requiring compliance with FSMA and you are exempt from the regulation, you may not have to do anything related to the regulation. Also, I can see third party audits, like the Harmonized GAPs audit, being updated to align with the rules to make sure that growers who have audits done meet the federal regulations as well.”

Increased interest in food safety

Even before the final rules were released, Bihn said she is receiving increased inquiries from greenhouse growers about food safety. “Greenhouse growers are trying to decide if they are subject to FSMA rules and how the required practices might fit with what they do with their greenhouses,” she said. “They are trying to figure out if they need to be concerned with meeting food safety regulations. They are going to be in the same situation as field farmers and asking the same questions. Are buyers asking the growers to meet the regulations? Greenhouse growers not subject to the regulations could easily get pushed into following the regulations if their buyers tell them in order to do business with them, the growers must follow the regulations.”

Bihn said her job is to help guide produce growers, whether they are field farmers, urban farmers, greenhouse growers or CEA growers, toward implementing food safety practices.

“Initially there may be frustration, hostility and denial,” she said. “All of those things will occur when growers first hear what they have to do. When they finally sit down and start to learn something about food safety and start to ask how can I fix this, then they start to make progress really fast.

“I love farmers who question everything. They don’t understand why doing something is a risk. They tell me I’ve never killed anyone so what’s the problem. That’s the engagement that I need to get them to think about it. They need to get to where they understand all farms can have produce safety risks and admit that they need to learn something about food safety so that they can make adjustments within their operations and put practices in place to reduce the risks.”

Industry job opportunities

Bihn said she has been encouraging Cornell students majoring in horticulture to get a minor in food science. She has also been encouraging students majoring in food science who are interested in produce safety to get a minor in horticultural production.

“There are food science students who have no idea how farms operate,” she said. “Unfortunately this sometimes results in food science professionals offering ideas for problem solving that may not be doable.”

Bihn said that food safety has traditionally been housed with the food science departments and crop production has been housed with the horticulture department.

“It’s time for there to be some cross pollination between these two departments,” she said. “It has been slow to happen. We now have a Masters of Professional Studies degree at Cornell that merges horticulture and food science. There are jobs out there, but they are difficult to fill because there are people who know production or there are people who know food pathogens, but there are very few people who know both.”

Bihn said she has received requests from her horticulture colleagues at Cornell to give guest lectures on food safety and to collaborate on publications about incorporating food safety guidelines into field publications.

“The fruit and vegetable industry as a whole is certainly saying food safety is something that we need to be incorporating,” she said.


For more: Dr. Elizabeth Bihn, Cornell University, Department of Food Science; (315) 787-2625;

Produce Safety Alliance,

National Good Agricultural Practices Program,

David Kuack is a freelance technical writer in Fort Worth, Texas;


High tunnels enable growers to increase production of high-value berries

 High tunnels can be a part of a production system that allows growers to produce berries year-round while improving fruit yields and quality.


By David Kuack


High tunnels have different uses in different places, said Marvin Pritts, professor and chair of the Horticulture Section of Cornell University’s School of Integrative Plant Science in Ithaca, N.Y.


“In California, many growers use the tunnels for rain exclusion,” Pritts said. “In other places, tunnels are used to help cut down on the wind and to regulate temperatures. In the Northeast U.S. the tunnels work in multiple levels. They offer protection from rain. They also offer some temperature and wind control. Their only limitation in the Northeast is the length of the seasons.”

Pritts said growers in the Northeast have been using high tunnels for about 15 years.


“We have plenty of water, good soils and the population,” he said. “It has been exciting for growers to see the response of the plants grown in the high tunnels. Growers have been able to extend production by about a month on either side of the growing season so that it is earlier or later.”

Pritts said growers of tomatoes, cucumbers and greens have taken the most advantage of using the tunnels.

“Growers who produce tomatoes were the first ones who really got into using the high tunnels in a major way,” he said. “That was followed by cucumbers. These tunnels were used for summer vegetable production. During the cooler season there are a lot of greens produced, including spinach, arugula and some other greens that can almost be grown year-round in tunnels.

“Vegetable growers have been able to extend their production season for a longer period than ever before. Also, growers have been able to produce some crops, like blackberries and figs, that typically don’t grow here in the Northeast. Tunnels allow growers to overwinter these crops.”


Supplying local markets

Pritts said in the Northeast most of the crops are being grown for local sales. “The growers supply local grocery stores like Wegmans and farmers markets,” he said. “Wegmans has its own farm where it is using high tunnels to grow various crops for its own stores.”  Wegmans Organic Farm in Canadaigua, N.Y., uses high tunnels to grow year-round at the 50-acre operation.

Pritts said he expects water restrictions in places like California will cause more growers to look at incorporating high tunnels into their production.

“At some point more of the production is going to have to shift eastward,” he said. “Growers in the Northeast don’t have a long season, but high tunnels offer some control. It makes sense to grow some of these crops locally where the markets are, where there is enough water and it’s relatively inexpensive to ship crops locally rather than shipping them across the country.”


Growing raspberries year-round

Pritts said growers in the Northeast are using high tunnels to harvest red raspberries earlier in the summer and to extend the production into the fall. Because the use of tunnels for berry production is a recent development, Pritts doesn’t really know which season the growers are using the tunnels for more. He expects it’s both.


Most of the high tunnel research that Pritts has done has been with primocane fall-bearing raspberries. These plants can be mowed down to the ground in the spring and they grow up and flower and fruit in the fall. Pritts said the canes can be pinched so that the plants flower and fruit later into the fall.

Marvin Pritts at Cornell University said growers could use
a combination of fall- and summer-fruiting raspberry
varieties along with outdoor field and high tunnel production to produce a crop year-round.Photos courtesy of Marvin Pritts, Cornell Univ.


“In October, raspberries aren’t available from field-grown plants in the Northeast because the temperature is too cold,” he said. “High tunnels allow raspberries to be picked in October when other locally-grown berries aren’t available. Growers in southern states are already done with their fall production. There also aren’t a lot of berries coming in from other parts of the world at this time. For those countries in the southern hemisphere, it would be too early to be harvesting berries. There is an opportunity for local growers in the Northeast to take advantage of limited
market supplies. It’s a niche market.”

Pritts said growers also have the option of growing summer raspberries producing fruit in late June and early July.

“Summer production requires more trellising because the canes have to be maintained through the winter,” he said. “If a grower produces summer raspberries, the high tunnels have to be kept up year-round. With fall production, since the canes are cut back, the plastic covering on the tunnels can be removed for the winter. Since the covering is going to be removed, the tunnel structure doesn’t have to be as strong because snow loads aren’t an issue.

Pritts said being able to take the plastic off of the tunnels is a real advantage during the winter for the fall raspberries.

“Some of the salts in the soil can be leached out with the normal snow and rain during the winter,” he said. “Then the plastic can be put back on. If the raspberries are being grown in containers, then the growing medium can be flushed to leach out excess salts.”

Pritts said if a grower is producing summer raspberries or blackberries, the plants have to be brought through the winter in a tunnel.

“During a typical year, raspberries and blackberries make it through the winter in a tunnel just fine, although these past two winters were exceptions,” he said. “But the high tunnel has to be able to support the snow loads in order to protect the plants. During heavy snow storms, especially if the snow is wet, the snow needs to be removed from the high tunnel to prevent it from collapsing. These structures don’t usually handle more than a foot of snow.”

Pritts said it should be easier for growers to produce fall-fruiting raspberries.

“Fall raspberry varieties can produce a summer crop, but typically these varieties are grown solely as a fall crop,” he said. “If these plants are grown as a fall crop and allowed to go through the winter, they will produce a small summer crop. Most growers prefer to choose varieties specifically for summer production.”

Pritts said a grower could use a combination of fall- and summer-fruiting varieties along with outdoor field and high tunnel production to produce a raspberry crop year-round.


Differences in yield, quality

Pritts said one of the major reasons growers are producing raspberries in high tunnels is because of the difference in fruit quality.


One of the major reasons growers are producing raspberries
and blackberries (shown) in high tunnels is because of the
difference in fruit quality, including having a longer shelf life.


“Tunnels keep rain off of the fruit so that it doesn’t get moldy as fast as field-grown berries,” he said. “The quality is like day and night between raspberries grown in high tunnels and those grown in the field. Tunnel raspberries definitely have a much longer shelf life.

“In regards to flavor, the raspberries grown in tunnels are so high yielding that they are not as sweet as field-grown berries. Because the yields are so high in tunnels, it is hard for the plants to provide sugar to all that fruit. Even though the tunnel berries may be less sweet, the yields are so much higher. If someone ate the tunnel raspberries and didn’t have the field raspberries to compare them too, they would say the tunnel raspberries were very good tasting.”


Improving plant performance

Pritts said field-produced raspberries generally have a 10-year life span for the field they are being grown in.

“After a couple years for field-grown plants, there tends to be a decline in fruit production,” he said. “In high tunnels we never fertilize, but we amend the soil with compost before we plant. We don’t have to fertilize because the vigor of the plants is already good. There hasn’t been any decline in the yields of the high tunnel plants even after 10-12 years.”

Pritts said high tunnel plants aren’t exposed to the same environmental stress plants encounter in the field.

“Soil pathogens survive when the soil is wet for long periods of time,” he said. “In outdoor fields the soil is going to stay wet for long periods. Many of the disease pathogens also like cooler temperatures. I expect these pathogens gradually take the plants down in the field. In tunnels there usually aren’t long periods of standing water as would occur in outdoor fields.”

Another benefit of the high tunnels is wind exclusion.

“The stems on the raspberry canes are very thin and there is a lot fruit at the top of the plants,” Pritts said. “When the wind starts to blow, it whips the field-grown canes back and forth. This doesn’t happen in the tunnels. Previous research has shown the wind can be very detrimental to raspberry yields.”

Since the plants grown in tunnels aren’t exposed to the rain, drip irrigation is used to water the plants.

“Irrigation in the tunnels is between the plant rows,” Pritts said. “Outside when it rains the weed seeds germinate. In the tunnels there’s not much weed pressure at all.

“Another advantage of the high tunnels is the fruit can be harvested even when it’s raining, when it’s cold or when the wind is blowing. People don’t want to harvest in inclement weather. The tunnels enable a grower to schedule berry harvesting.”

Pritts said raspberry growers who use tunnels have to closely monitor plants for two-spotted spider mite.

“The difference in the populations of two-spotted mite is the biggest issue,” he said. “Outside, often times, growers don’t have to be concerned with mites. The mites are in the field, but they are at very low levels. They don’t like being wet so when it rains it depresses the populations. In the high tunnel where it doesn’t rain, there is a dry environment, which the mites thrive in.”


For more:
Marvin Pritts, Cornell University, School of Integrative Plant Science,
Horticulture Section, Ithaca, NY 14853; (607) 255-1778;


Other sources of information on the production of high tunnel berries:



Low tunnel strawberries


Marvin Pritts, professor and chair of the Horticulture Section of Cornell University’s School of Integrative Plant Science is also doing a study on the production of strawberries in low tunnels. He is growing day neutral strawberries, which flower and fruit nearly all summer into the fall, in low tunnels.

“The strawberries are planted on a double row on a 16-inch raised bed with white plastic,” he said. “Hoops, which are covered with plastic film, go about 18 inches above the plants. The plastic is held down on the hoops with bungee cords.”


Marvin Pritts said it is about four times cheaper on a
per area basis to grow strawberries in a low tunnel
than in a high tunnel.


Pritts said the plastic film helps to keep the temperatures lower during the summer. The covered tunnels also retain some heat during the fall.

“The sides of the tunnels remain up almost all the time,” he said. “When it rains or it’s going to be cold or windy, the tunnel sides are lowered. The strawberries produce high quality fruit which can be grown nearly year-round.”

Pritts said it is about four times cheaper on a per area basis to use a low tunnel than it is to use a high tunnel because a tall hoop structure isn’t required.

“The plants only grow low to the ground so there’s no need to construct a 15-foot tall structure,” he said. “Like in the high tunnels, the plants in the low tunnels are watered and fertilized with drip irrigation. The drip line runs down the middle of the bed between the two rows of plants.”


David Kuack is a freelance technical writer in Fort
Worth, Texas;

Meeting the fertilization needs of greenhouse lettuce

Greenhouse lettuce can be a successful container or
hydroponic crop for ornamental plant growers looking to give edibles a try.

By David Kuack
Ornamental plant growers considering producing an edible
greenhouse crop may want to try lettuce. Neil Mattson, associate horticulture
professor at Cornell University, said lettuce is a plant with moderate
fertility needs.
“Grown hydroponically, lettuce has somewhat lower
fertility needs than a greenhouse tomato crop,”

Ornamental plant growers interested in growing edible
crops may want to try lettuce. It can be produced in
containers with a growing medium or hydroponically
in troughs or a float system (pictured).
Photos courtesy of Cornell University

Mattson said. “Grown as a
container crop, lettuce is relatively similar to petunia. However, lettuce has somewhat
greater calcium needs. Growers can produce a relatively good crop of lettuce in
containers, if they use a complete fertilizer at a moderate strength of 150
parts per million nitrogen.”

Mattson said head lettuce can be produced in containers similar
to a bedding plant crop. The seed would be planted into a plug tray for three
to four weeks. Transplanting the plugs into larger containers, the crop could
be finished in four to six weeks depending on light and temperature levels.
He said baby leaf lettuce can be grown in flats. The seed
is directly sown into the growing medium and grown for three to four weeks
until plants reach suitable size.
Calcium deficiency

Leaf tipburn is a physiological disorder that can occur
when growing greenhouse lettuce. It can greatly impact the salability of a

“The main reason that tipburn occurs is the lettuce is
growing too fast under high light,” Mattson said. “For lettuce, the target
daily light integral is 17 moles per square meter per day. The light level should
be lower if there is poor air flow. If the light level goes higher than 17
moles, the rapid growth of young leaves is affected. There may be an inadequate
calcium supply, especially as the lettuce heads begin to mature and close. If
there is not enough air flow and not enough transpiration by the young leaves,
then not enough calcium can reach the leaves through the xylem sap. This can
cause tipburn to occur. It’s a case of pushing the plants too fast.”
tipburn in lettuce is not a result of a lack of calcium
supplied to the plants,
but an inability of the plants to
transport enough calcium to the young leaves.
Mattson said in many cases, tipburn is not a result of a
lack of calcium supplied to the plants, but an inability of the plants to
transport enough calcium to the young leaves.
“For container-grown lettuce, there is typically enough
calcium if the growing medium has a lime charge and if the fertilizer water
solution contains more than 50 ppm calcium,” he said. “Many common bedding
plant fertilizers, including 20-20-20, 20-20-20 and 21-5-20, do not contain
calcium. These fertilizers are typically used with tap water sources that
contain moderate alkalinity. In many cases, these tap water sources also
contain sufficient calcium.”
Mattson said it is important for growers to test their
water sources to make sure adequate calcium is being supplied, either from the
water source or added into the fertility program. If calcium needs to be added,
calcium nitrate is most commonly used. However, calcium nitrate is not
compatible with most complete fertilizers.
“Usually if a grower has to add calcium, it can be done
using a separate stock tank or a separate injector,” Mattson said. “One
strategy is to use a separate injector for the calcium nitrate in a series with
a 20-10-20 fertilizer that is being added with a second injector. Adding 50 ppm
calcium from calcium nitrate should be sufficient.
“An alternative method of calcium application, if a
grower has only one injector is to rotate between two separate stock tanks, one
for calcium nitrate and one for the bedding plant fertilizer. A grower would then
rotate between the two fertilizers. For example, for two days he would use the
20-10-20 fertilizer and on the third day he would use the calcium nitrate
applied at 150 ppm.”
Production with
organic fertilizers

Mattson has been able to grow a relatively good crop of
container-grown lettuce using granular organic fertilizers incorporated into
the growing medium.

“We incorporated poultry-based organic fertilizer (Sustane
8-4-4) into the growing medium at a rate of 8 pounds per cubic yard for both
the seed germination and transplant growing mixes,” he said. “That provided
good fertility, but for optimum yields I would also suggest making some liquid
organic fertilizer applications, maybe two to three times a week as the plants
get older.”
Mattson said the organic granular fertilizer he used is
temperature-dependent and is broken down by soil microbes. Sustane 8-4-4 has a
45-day release period, but under very warm greenhouse temperatures Mattson has
noticed quicker release rates. He said there are other slow release organic
fertilizers with different release periods. For example, Verdanta EcoVita lists
a 75-100 day release period.
electrical conductivity and pH

One strategy that Mattson recommends growers do periodically
is to monitor the electrical conductivity (EC) and pH levels.

“Monitoring EC will help growers determine if the plants
are receiving sufficient fertility,” he said. “If a grower is incorporating a
slow release fertilizer, this is a good indicator of when additional fertilizer
needs to be added. An under-fertilized plant will show yellow lower leaves from
nitrogen deficiency.”

electrical conductivity (EC) can help avoid
under fertilizing lettuce plants,
which show yellow
lower leaves caused by nitrogen deficiency.

Mattson said monitoring pH is important as it impacts
nutrient availability. He said lettuce isn’t commonly susceptible to iron
deficiency, but it will start to show up when the pH starts to increase above
“Monitoring EC and pH is especially important in
hydroponics,” he said. “A good grower who is producing his crop in a growing
medium in containers will monitor the pH every week or two. The pH may change
over the course of a week by maybe one unit.
“Growing hydroponically, a grower should be monitoring
the pH every day and make adjustments. Depending on the type of fertilizer and
the quality of the water, the pH in a hydroponic set up could change two units
in a day.”
Optimizing lettuce

Mattson said light and temperature are going to be the
drivers for how long it takes to finish a lettuce crop. Whether a grower is
producing the crop in containers with growing medium or hydroponically
shouldn’t have any effect on the length of production.

He said plant spacing can also impact the size of the
lettuce head. If plants are grown in small containers and spaced pot-to-pot,
the lettuce heads may not reach full size.
For greenhouse lettuce, Cornell University researchers
developed a hydroponic production model that enables growers to produce a
lettuce crop from seeding to harvest in 35 days if temperature and light
intensity are at optimum levels.
“When the light level isn’t optimized, a lettuce crop can
take more than 100 days from seeding to harvest,” Mattson said. “High pressure
sodium lamps would be the best lamps to use if a grower is looking to provide
supplemental light in a greenhouse to increase the daily light integral. For
the Cornell model we adjust the amount of light in the greenhouse based on the
amount of outdoor light. Seventeen moles per square meter per day is the daily
light integral we are aiming for with the model. The optimum temperature for
plant development is about 75ºF
during the day and 65ºF
at night.”

For more: Neil
Mattson, Cornell University, School of Integrative Plant Science; (607)

David Kuack is a freelance technical writer in Fort
Worth, Texas;

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Growing through the California drought

Bill Phillimore, executive vice president at Paramount
Farming Co. in Shafter, Calif., spoke at this year’s Seeley Summit which
focused on water. Phillimore, whose company is a producer of a variety of tree
crops, discussed the impact the drought has had on water availability and
trying to operate under severe water restrictions.

By David Kuack
This year’s Seeley Summit focused on “Water: Horticulture’s Next Game Changer?
Nowhere is the effect of water or lack of it more pronounced than in
California. Bill Phillimore, executive vice president at Paramount Farming Co.
in Shafter, Calif., knows firsthand the effects drought can have on an
agricultural producer. Phillimore’s administration responsibilities include the
handling of water and power issues.

Bill Phillimore, executive vice president at
Paramount Farming Co., whose responsibilities
include water and power issues, knows firsthand the
effects drought can have on an agricultural producer.
During this year’s Seeley Summit, Phillimore shared his
company’s experience dealing with severe drought conditions. He sat down with
Hort Americas to discuss what his company has experienced and what it is doing
to continue producing its crops during the drought.
1. How many acres
of production does your company have in California this year?

Paramount is farming more than 100,000 acres in 2014 with
a combination of citrus, almonds, pistachios and pomegranates.

2. How many acres
has your company taken out of production because of the drought?

We have managed to secure sufficient water for these
crops in 2014, but at very considerable expense. In some instances we are
applying less irrigation water than we would optimally prefer.

3. Has your
company ever faced the type of water restrictions it is facing in California
this year?

We have never faced water restrictions this severe in
California previously.

4. What is the
primary source of water for most of the crops your company is producing in

Due to our size our water comes from a number of
different sources, including the State Water Project, exchange contractors and
the Kern River. In almost all instances, this water is supplemented by
groundwater which is being particularly heavily used in 2014.

5. What methods of
irrigation is your company using to water the crops? Were these the primary
irrigation methods prior to the occurrence of the severe drought conditions?

All our property is irrigated with drip or micro
sprinklers as it has been for more than the last 20 years. The drought has not
changed our methods of irrigation because we made the change to more efficient,
practical systems some years ago.

Paramount Farming Co. is farming more than 100,000 acres
this year with a combination of citrus, almonds, pistachios
and pomegranates.
6. During your
presentation at this year’s Seeley Summit you discussed how your company used previous
research to determine when specific plants need to be watered. Based on the
company’s findings, have you been successful at manipulating the water delivery
without having a negative impact on the plants?

We hope that we have timed the application of water,
especially in those crops where there has been reduced amounts, so that there
has been no negative effect on plants or yields. Although in determining the
schedule we have relied heavily on previous experiments conducted on our
property, this is obviously being done on a far greater scale and thus it is
not currently easy to assess either the long or short term effects.

7. During the
Seeley Summit you mentioned that some of the crops currently being grown in
Kern County, Calif., are unique to this region? Can you give some examples of
these crops and what is unique about the conditions under which they are grown?

In Kern County, where we have the majority of our
acreage, we share climate with the rest of the Central Valley in California
with some slightly greater extremes and different soil conditions. All these
environmental factors, which allow dormancy in the winter, but not usually
extreme low temperatures, and hot, dry summers, are particularly suited to the
production of pistachios, almonds, table grapes, carrots and citrus.

8. During the
Seeley Summit you discussed the Bay Delta Conservation Plan. Can you describe
what this plan is about?

Most precipitation in California occurs in the north of the
state while the majority of the usage, both urban and agricultural, occurs
south of the Sacramento-San Joaquin River Delta. One of the greatest challenges
that California has is how to move water through the delta to southern
California without environmental damage.

There is currently an ongoing process, otherwise known as
the Bay Delta Conservation Plan (BDCP), to move the point of diversion from the
south delta to the north delta and as part of the permits needed from the
federal wildlife agencies (U.S. Fish and Wildlife Service and National Marine
Fisheries Service) have a 50-year habitat conservation plan which would put an
end to the constant litigation of the delta. Our company is very interested in
this project and believes it is extremely important for the economic future of
the whole state.

Applications of reduced amounts of water to Paramount’s crops
are based on experiments conducted at the farm aimed at
avoiding any negative effects on the plants or their yields.

9. During the
Seeley Summit you expressed concerns that some agricultural trade associations
and other agricultural producers could be doing more to help ensure that
growers continue to have adequate water supplies. Could you please elaborate on
how you would like to see these groups become more involved with water-related issues?

I did express concern during the Seeley Summit that all
trade organizations do an adequate job of representing their members because
they do not always understand all the issues that they are being asked to
address. These organizations often spend too little time consulting their
members, especially when the organizations are covering a broad range of issues.
I do believe that all farmers of whatever size need to be conscious of this
fact and that unfortunately there is no substitute for their personal
For more:
Paramount Farming Co., (661) 399-4456;

David Kuack is a freelance technical writer in Fort
Worth, Texas;

Visit our corporate website at

e-GRO website becoming major information resource

U.S. university floriculture professors and extension
specialists have collaborated to bring the floriculture industry an extensive
and thorough information resource.

By David Kuack

If you aren’t familiar with the e-GRO website,
it is one anyone involved in floriculture should check out. How good is the
website? This summer the American Society for Horticultural Science presented
the website’s developers with its Extension Educational Materials Award.

The American Society for Horticultural Science presented
the developers of the e-GRO website with its Extension
 Educational Materials Award

The two-year-old e-GRO: Electronic Grower Resources
Online website was the brainchild of Brian Krug, extension greenhouse and
horticulture specialist at University of New Hampshire, Brian Whipker, extension
floriculture specialist at North Carolina State University, Roberto Lopez,
floriculture extension specialist at Purdue University, and Nora Catlin, floriculture
specialist at Cornell Cooperative Extension of Suffolk County.

“A few years ago Brian Whipker, Roberto Lopez and I were
travelling together,” said Brian Krug. “We were discussing how difficult it was
to prepare an extension newsletter. Roberto had the idea of doing a newsletter
collectively. We invited Nora Catlin, who is a plant pathologist, to join us in
creating the e-GRO Alert newsletter. The newsletter is funded by the American Floral Endowment.

“Rather than doing a traditional monthly or quarterly
newsletter we decided to do a seasonal weekly newsletter based on what we saw
going on in commercial greenhouses. The primary focus is what is happening in
greenhouses during the spring season beginning at the end of January through
May. Sometimes we prepare more than one newsletter during the week depending on
the issues that are occurring in commercial greenhouses.”

Providing growers
a “heads up”

Krug said that although there is a tentative schedule as
to what is going to be written about during a specific week, the topic and
author can change depending on what growers may be dealing with. The
newsletters cover a variety of grower-related issues including disease and pest
management and environmental, physiological and nutritional disorders being
observed in commercial greenhouses.

“At the end of January we may schedule an article on
plant growth regulators written by Brian Whipker, but that will depend on what
he has seen occurring in growers’ greenhouses,” Krug said. “Ours is a very
reactionary industry. With the Alert newsletter we are trying to give the
growers a heads up as to something that they might already have in their
greenhouses or may be something that is coming their way.”

During the second year the team of specialists expanded
to include Cornell University entomologist Dan Gilrein, University of Georgia
floriculture professor Paul Thomas and Virginia Tech horticulture professor and
Virginia Cooperative Extension specialist for greenhouse crops Joyce Latimer.
Joining the group in 2014 will be Kristin Getter, who is the floriculture
outreach specialist at Michigan State University.

“The bulk of the e-GRO Alert subscribers are from the
authors’ respective states,” Krug said. “We have subscribers in 48 states and
over a dozen different countries.”

greenhouse basics

Another part of the website is e-GRO University. This
section was developed by Krug, Whipker, Lopez, Kansas State University
floriculture professor Kim Williams, Kansas State ornamental and horticultural entomologist
Ray Cloyd and Cornell University senior extension associate and plant
pathologist Margery Daughtrey. e-GRO University is the second phase of the
website which includes over 60 videos that cover the basics of greenhouse
production. The videos are divided up into five different sections: greenhouse
management, nutrition management, growth management, insects and mites, and diseases.
e-GRO University has been funded by the Gloeckner Foundation for two years.

 e-GRO University provides a Greenhouse 101 curriculum
that covers basic information for greenhouse management
 and production.

“For e-GRO University we developed a Greenhouse 101
curriculum that provides basic information for greenhouse management and
production,” Krug said. “It is information that would be comparable to a
freshmen and sophomore college course program. Our goal was to provide an
educational resource for people who work in the industry who didn’t receive a
formal education in greenhouse production. If you are grower in a greenhouse without
the formal training or education, this program allows a person to get a handle
on some of the basics on nutrition, insects and diseases. A person can choose
to listen to any of the videos, which run 20 minutes or less. Most of the
information is basic concepts so it is not going to be changing.”

Krug said the e-GRO team is looking to set up a
certificate program for e-GRO University.

“Listening to any of the programs is free,” he said. “The
certificate program will enable interested growers in holding themselves
accountable and will indicate that a person successively completed the
lectures. The certificate will indicate that a person successfully completed
e-GRO University. There will be five different modules and a quiz at the end of
each module. A person will be able to choose how many of the modules they want
to complete.”

Krug said the e-GRO University program can also be used
by growers for new employees who don’t have any experience or limited
experience in different aspects of growing.

“By offering a certificate program to employees, this
enables employees to be held accountable for the modules that they have
completed,” he said. “We’re hoping that employers will use this for their
employees. We wanted to offer something more for the greenhouse employees.”

Krug said the e-GRO University program can also be used
by vocational teachers who have access to a greenhouse and who may need to
familiarize themselves with the basics before they and their students try to
start growing plants in the facility. This could be a continuing education
program for the teachers as well as a learning resource for the students.”


Other resources available to visitors of the e-GRO
website include:

* Webinars.
This is the newest resource being offered by the e-GRO. The series kicks off
with “Poinsettia Troubleshooting,”
a two-hour webinar on Sept. 18 that will focus on troubleshooting poinsettia
problems. Ray Cloyd will discuss key insect identification and control issues.
Brian Whipker will focus on nutrition disorder identification and management. North
Carolina State University plant pathologist Kelly Ivors will cover disease
identification and control.

* Podcasts. About 200 podcasts have been
completed by members of the e-GRO team in cooperation with Greenhouse Grower
magazine over the last three to four years. Krug said linking the podcasts on
e-GRO enables growers to search for the episodes they want to view.

* e-GRO Bookstore. Brian Whipker has created five
electronic books that are available for the iPad. Krug said that Whipker plans
to continue to create new books for the library. Books currently available

1. Selecting and Using Plant Growth Regulators on
Floricultural Crops. This free publication was done in collaboration with Joyce
Latimer at Virginia Tech and Brian Whipker at North Carolina State University.

2. e-GRO Volume One: Poinsettia
3. e-GRO Alert Volume Two
4. e-GRO Volume Three: Primula
5. e-GRO Alert Volume Four: Sclerotinia

* Floriculture InfoSearch. Although this resource is independent of the e-GRO team, the
members felt it was worth adding to the website. John Dole, professor and head
of the Department of Horticultural Science at North Carolina State University,
partnered with American Floral Endowment to create the Floriculture InfoSearch
engine. This search engine provides convenient and comprehensive access to
floriculture literature, videos and presentations. Information is available from
scientific literature and trade and association magazines and websites. The
Floriculture InfoSearch website also contains a floriculture archive with
materials dating back to the early-1800s from AFE, North Carolina State,
scientific journals and trade publications.

For more:
Brian Krug, (603) 862-0155;

David Kuack is a freelance technical writer in Fort
Worth, Texas;

Visit our corporate website at

Using Supplemental Lighting in Greenhouse Vegetable Crops

Why you should consider lighting greenhouse vegetable crops.

Can’t decide if it would be worth installing supplemental lights for your greenhouse vegetables? A combination of supplemental light and carbon dioxide can ensure that you are maximizing plant growth.

Melissa Brechner, director of the Controlled Environment Agriculture Center for Technology Transfer at Cornell University, usually tells greenhouse vegetable growers that supplemental lighting is worth the investment.

“It depends a little on the scale of the greenhouse facility,” Brechner said. “It also depends on the crop and what’s the market. If you are growing in November, December, January and February in some of the darker locations in the country, which covers a sizable area, you absolutely need supplemental lighting, if you want to have maximum production.”

Brechner said a greenhouse vegetable grower is going to need a minimum of 15 moles of photosynthetically active radiation (PAR) per day in order to produce a crop.

“For Ithaca, N.Y., and for many other places, the light levels range from a high of 15 moles per day in January up to about 65 moles per day in July,” she said. “Those levels are not going to change drastically whether a grower is in Arizona or in Ithaca. What is going to change is that in Arizona there aren’t the really dark 0 and 1 mole days that occur in Ithaca.

“For tomatoes and cucumbers I tell growers that they should have more than 20 moles per day to produce a good crop. I don’t know how different production would be if the light level was 30 moles per day. Is it worth the extra 10 moles for the grower to put in supplemental lighting? I’m not sure. But it is certainly worth it for a grower to go from 1 to 10 moles and from 10 to 20 moles.”

High, low light issues

Although greenhouse vegetable growers associate more problems with low light levels, Brechner said high light levels can also cause problems with some crops.

“Growers can have problems with both high and low light levels depending on the season in which the grower is trying to grow and where in the country he is located,” she said. “If a greenhouse lettuce grower is trying to grow in Georgia in August or even October, he is going to have a problem with too much light. The grower better have a shade curtain in the greenhouse or he is going to have tip burn problems.

“In Massachusetts in December the issue is going to be not having enough light. I have talked to growers in the Northeast who have told me that they don’t use any supplemental light and they don’t use much heat, but it take them three months to produce a crop. If they were lighting and heating, they could finish that crop in 35 days. Also, in the Northeast the growers are going to have less than 15 moles per day outside light. And depending on the glazing the greenhouse is covered with is going to determine what percentage of light will make it into the greenhouse. It is going to be somewhere between 65 percent on the low end and 90 percent on the high end depending on a number of factors.”

Brechner said the amount of PAR light that reaches the plants is a function of:
1. the angle of the sun in relation to the glazing,
2. what the glazing material is made of,
3. the cleanliness and condition/age of the glazing,
4. shading from greenhouse structure components, and
5. type of light (direct or indirect).

<style=”text-align: center;”>A greenhouse vegetable grower is going to need a minimum of 15 moles of photosynthetically active radiation (PAR) per square meter per day in order to produce a crop.
(Photo courtesy of Cornell University)

Optimum light levels

Brechner said that growth is directly correlated to the amount of light the plants receive, especially when they are in a vegetative state.

“I think lettuce is a less forgiving crop. Tomatoes and cucumbers if you don’t give them as much light they will still grow,” she said.“Lettuce should have 17 moles of PAR per square meter per day. This refers to the combination of natural light that is transmitted through the glazing as well as any artificial light that is used.

Our research has shown that an average of 17 moles gives optimal growth while minimizing tip burn. Brechner said there are some differences in the amount of light that different types of lettuce will tolerate.

“We’ve found for Boston (bibb) lettuce that a daily light integral of 17 moles of light per day used with vertical airflow to increase the rate of transpiration in order to increase calcium uptake prevents leaf tip burn,” she said. “Romaine lettuce can’t take as much light before it gets tip burn. And it certainly can’t take as much light without having vertical airflow.

“Lettuce grown outside receives more than 17 moles of light per day, but it is windier outside. Lettuce, especially romaine, grown outside will get tip burn if there is too much light. Even during December you can find field-grown lettuce coming from California that is tip burned.”

Greenhouse vegetable growers can have problems with both high and low light levels depending on the season and where in the country an operation is located.
(Photo courtesy of Cornell University)

Controlling light, CO2 levels

Cornell researchers have developed a light control algorithm that controls for daily light integrals. It’s called LASSI (Light and Shade System Implementation). The software interfaces with the greenhouse environmental control computer to turn on the supplemental lighting or to pull the shade curtains.

“Every hour of the day LASSI goes through a series of rules and makes the decision to turn the lights on or to pull the shade,” Brechner said. “It seeks to optimize the use of off-peak power. Most greenhouse operations have off-peak power rates which are usually from 11 p.m. until 5-6 a.m. The power at that time is significantly cheaper.

“This program can get a little tricky with tomatoes because they need four hours of darkness every day or they don’t grow well. Lettuce does not need this dark period.”

Brechner said LASSI can be used with any crop as long as the grower knows the appropriate target daily light integral. “We have used it (LASSI) with tomatoes that need a 4 hour dark period to grow normally,” she said. “Optimum DLIs have not been published in peer-reviewed literature. We have investigated a range of DLIs for lettuce from very low (8 moles) to high (22 moles). A similar set of DLI vs. production curves would be useful for all typical greenhouse vegetable crops, but I am not aware that they exist.”

Brechner said growers have the option of using supplementing carbon dioxide to substitute for a certain amount of light.

Table 1. Cost of supplemental lighting with and without the use of supplemental carbon dioxide.
With CO2     Without

Annual cost, supplemental lighting     $8,638          $17,151
Annual cost, supplemental CO2               $1,426           $0
Annual cost, total                                $10,064         $17,151
Hours using lights                               1,361             2,665
Off-peak %                                         75                  72
kWh electricity for light                      135,120         264,581

“For example if a grower supplements with 1,600 parts per million carbon dioxide, he can use half the amount of light and get the full amount of growth,” she said. “Adding carbon dioxide makes photosynthesis more efficient allowing the plants to fix more carbon with less light.”
Cornell has developed two versions of the LASSI program:
the original LASSI and CO2 LASSI, which take into account whether it’s cheaper for a grower to supplement with carbon dioxide or with light.

“For our fifth of an acre CEA greenhouse growing lettuce with supplemental carbon dioxide, the lighting cost would be $8,600 (see Table 1). The lighting costs would increase to $17,000 without the carbon dioxide,” she said. “The supplemental carbon dioxide costs are about $1,400 a year. Total cost for the supplemental lighting and CO2 for the CEA greenhouse simulation is $10,000 with supplemental carbon dioxide vs. $17,000 for supplemental lighting without carbon dioxide. Supplementing with carbon dioxide enables a grower to use half the supplemental light and still hit the daily light integral target every day. This enables the grower to achieve a consistent harvest every day of the year. The grower is basically pushing the plants as hard as he can without getting tip burn.”

Research at Cornell University has shown that an average of 17 moles of PAR per square meter per day gives optimal growth of lettuce while minimizing tip burn.
(Photo courtesy of Cornell University)


For more:
Melissa Brechner, Cornell University, Controlled Environment Agriculture Center for Technology Transfer; (607) 255-8146;;

David Kuack is a freelance technical writer in Fort Worth, Texas;
Visit our corporate website at