How you grow and process fresh cut basil will impact the flavor and shelf life of the harvested product.
Basil is one of the most popular culinary herbs. Whether grown as a potted crop or for fresh cut sales, basil is an herb that’s in demand year-round. Growers looking to add edibles to their product mix should consider basil to be a must-have herb in their product offerings.
Incorporating dissolved oxygen into hydroponic production systems during warmer temperatures can help improve plant growth and reduce crop time.
Trying to grow hydroponic crops like leafy greens can be a real challenge during warmer times of the year. Growers have few options to lower temperatures, including cooling the greenhouse and/or water temperature. Another production technique that is being used by hydroponic growers in the United States and Australia is to introduce dissolved oxygen into the fertilizer tank solution.
“We’ve heard anecdotal reports that increasing dissolved oxygen levels can help prevent some root diseases like Pythium and other root rots,” said Tyler Baras, special projects manager at Hort Americas in Bedford, Texas. “We’ve also heard that increasing dissolved oxygen can possibly improve nutrient uptake and improve overall growth. Another possible benefit with using dissolved oxygen is reducing tip burn on leafy greens.
“These are some of the main issues with growing in warm climates like Texas during the summer. With an increase in water temperature comes a higher disease pressure and chances for tip burn. This has occurred in both nutrient film technique and deep water culture systems.”
The optimum water temperature for lettuce is between 65ºF-70ºF. For basil the optimum water temperature is around 75ºF.
Baras said most of the references he has read for adding dissolved oxygen suggest incorporating 4-10 parts per million for leafy greens.
“Most growers that I know are adding between 6-7.5 ppm for leafy greens,” he said. “When growers start to go beyond that rate to reach a higher level they have to use something like compressed oxygen or ozone. These are the main two methods, which are more expensive, for achieving a higher dissolved oxygen rate. Most growers I know are using a less expensive Venturi system or an air pump with air stones to add dissolved oxygen.”
Trialing different levels of dissolved oxygen
Baras has been studying the impact different dissolved oxygen levels can have on butterhead lettuce, basil and arugula grown in deep water culture systems. He set up deep water culture systems with three different levels of dissolved oxygen: 2 ppm, 7.5 ppm and 29 ppm.
“We have been tracking growth and how it affects the morphology of the plants,” he said. “The 2 ppm dissolved oxygen rate is what we were able to achieve without doing any type of aeration. This was our control.”
In another system Baras used a Venturi attachment to a small submersible pump that drew in atmospheric air.
“The highest rate of dissolved oxygen that we could achieve using atmospheric air was a maximum of 8.5 ppm,” he said. “The rate hovers between 7.5 to 8.2 ppm, with it usually averaging 7.5 ppm.”
The third system is a high rate of dissolved oxygen that uses compressed oxygen tanks to deliver 29 ppm.
“This system uses nanobubble technology,” he said. “We were using a prototype device that forces oxygen into a solution in really small bubbles so that the oxygen stays in suspension longer instead of falling out. The lowest rate that we could set was 29 ppm. This level of dissolved oxygen is much higher than what most leafy greens growers are targeting.
“A lot of the flowering crop and cannabis growers who are incorporating dissolved oxygen are actually targeting these higher rates. These growers are achieving 20-40 ppm dissolved oxygen. The flower and cannabis crops tend to prefer to be grown on the dry side. With this type of nanobubble dissolved oxygen technology it opens up this production method to crops beyond leafy greens.”
Some dramatic results
Baras said he has seen some dramatic effects on plant growth with higher dissolved oxygen rates. At the beginning of the trials during the first month the water temperature in the fertilizer tanks was 80ºF. During the second month the water temperature was between 75ºF-80ºF.
“At 2 ppm the arugula plants were severely stunted and were unsalable,” he said. “At this low rate there were also some severe nutrient deficiencies. At 7.5 ppm the arugula looked normal with slight deficiencies. There weren’t any nutrient issues at the 29 ppm rate and the plants almost doubled in size.”
Baras said even at the low rate of 2 ppm some crops could still be marketable.
“The basil and butterhead lettuce could still pass as marketable at the low 2 ppm rate,” he said. “The plants were very small and it would take several more weeks of production to reach the target weights we were aiming for. At the 7.5 ppm dissolved oxygen rate the plants had fairly normal growth as to what we are used to seeing.
For butterhead lettuce at the 2 ppm rate the heads were smaller and compact. The core of the heads were tighter, but actually had a good shape. At the 7.5 ppm and 29 ppm rates, the heads had similar shapes.
For the basil there was an increase in height as the dissolved oxygen level increased. Overall the plant height and size increased at higher dissolved oxygen rates.
“At the 29 ppm rate, the plants looked like the plants at the 7.5 ppm rate, but they were about a week ahead,” Baras said. “Both of these rates produced plants with healthy looking morphology, but the plants receiving 29 ppm dissolved oxygen developed faster. On average all of the crops grown with 29 ppm were at least a week faster to finish to a marketable size.”
Differences in root growth
Baras said the roots for the crops in the three rates of dissolved oxygen had different growth patterns.
“The roots in the 2 ppm dissolved oxygen systems were very short and stubby and almost seemed to be retreating from the water,” he said. “The roots remained mostly in the stone wool rooting cubes.”
At the 7.5 ppm dissolved oxygen rate the roots were long and had a lot of lateral branching. Baras said they looked like standard hydroponic roots.
“At the high 29 ppm rate the roots actually had less lateral branching, but they were really white, long and thick,” he said. “But there was less lateral branching. It almost seemed like since there was so much oxygen in the water the plants didn’t need to have as much lateral branching.”
Even though there were differences in the root morphology, there was no significant difference in the root weight for all three dissolved oxygen levels. The average root weight for both the 7.5 ppm and 29 ppm rates was 0.8 ounces. The root weight for the 2 ppm rate was about 0.7 ounces.
For more: Hort Americas, (469) 532-2383; email@example.com; https://hortamericas.com.
David Kuack is a freelance writer in Fort Worth, Texas; firstname.lastname@example.org.
Trials with organic and conventional fertilizers in hydroponic production systems are showing it’s possible to produce edible crops at much lower nutrient levels.
How much different is it growing edible crops organically than it is with conventional production inputs? Hort Americas special projects manager Tyler Baras is studying the differences in trying to grow organically versus using conventional production methods.
Baras has been doing organic production research in a 12,000-square-foot greenhouse in Dallas, Texas, using four deep water culture ponds and a nutrient film technique system. The ponds measure 4-foot by 8-foot and are 10 inches deep. Baras said the ponds are smaller than what would be found in many commercial greenhouse operations, but said the pond size is common in vertical farm setups. Baras has been trialing commercial organic fertilizers including Pre-Empt and an experimental organic fertilizer. The organic fertilizers are being compared with crops grown with Hort Americas 9-7-37 hydroponic fertilizer with calcium nitrate and magnesium sulfate. All of the production systems have also been incorporated with the commercial microbial inoculant TerraBella. Crops being grown in the production systems include Italian basil, green butterhead and red butterhead lettuce.
Rethinking optimum nutrient levels
Baras said the deep water culture production results he has gotten with Pre-Empt organic fertilizer have been comparable to the crops grown with the conventional Hort Americas hydroponic fertilizer.
“With Pre-Empt we have been able to match the growth rates of the conventional salt fertilizer,” Baras said. “As a result of the growth rates we have gotten with the organic fertilizer, we have started to question the nutrient recipes that have been recommended for hydroponic edible crop production. Many of the traditional recipes for hydroponic production have a target level of 200 parts per million nitrogen. But we are seeing the same growth rates in the organic fertilizer ponds with 10 ppm nitrogen as the 200 ppm nitrogen conventional fertilizer pond.”
Baras said the electrical conductivity level in the organic fertilizer ponds has been as a low as 0.5 compared to 2.5 in the conventional fertilizer pond and the crops are coming out nearly identical in terms of production time and plant weight.
One difference between the organic- and conventional-grown crops is the time in propagation.
“The crops are finishing at the same time from transplant to harvest time, but we are keeping the plants an extra week in the seedling stage for the organic fertilizer,” Baras said. “We are running the seedlings for two weeks with the conventional fertilizer and about three weeks with the organic fertilizers.
“The organic plugs are started a week earlier, but they are transplanted on the same day as the conventional plugs. We want the roots coming out of the side of the plugs before we transplant them into the ponds. The seedlings are fairly similar in size when they are transplanted into the ponds.”
Once the organic and conventional plugs are placed into the ponds, they both spend the same amount of time there until the crops finish.
“The plants are coming out of the ponds with nearly identical weights,” Baras said. “Overall the seed to harvest time is faster with the conventional fertilizer, but that it is because we are able to transplant the plugs into the pond faster because the roots are coming out of the plugs sooner.”
Baras said the plants grown with the organic fertilizers have also shown they can be grown with lower levels of other nutrients. For example, with the conventional fertilizer the nutrient solution may contain 200 ppm potassium and the level is only 12 ppm with the organic fertilizers.
“Aquaponic growers have seen similar situations,” he said. “Some aquaponic growers may be running an EC of 0.7 with a relatively low nutrient level, but they are still seeing good growth.
We are seeing that as well with the organic fertilizers. There are low nutrient levels in the solution, but the crops are coming out the same and the leaf tissue analysis is nearly the same as well.
“For our trials the macronutrient uptake for the plants, even when they are grown in a low fertilizer concentration like 0.5 EC, they are still able to pull what they need out of the solution. Leaf sample analyses of butterhead lettuce and Italian basil grown in 0.5 EC organic fertilizer vs. 2.5 EC conventional fertilizer, most of the macronutrient levels in the leaves are very similar. It appears the plants are doing a good job of regulating the nutrient uptake to get what they need.”
Aging fertilizer solutions
Baras said letting the organic fertilizer solutions age in the ponds may have an impact on the availability of nutrients for some crops. The aging of the fertilizer solutions also has an impact on increasing the microbial population.
“We have definitely seen some differences in plant growth,” he said. “Our first crops of butterhead lettuce and basil did very well with Pre-Empt organic fertilizer. However, one of the other organic fertilizers we trialed grew a quality first crop of lettuce, but not the best looking basil. As we continued the trial with our second and third crops, the basil grown with the other organic fertilizer started doing much better. It appears the organic solutions in the ponds may need to age until the nutrients reach adequate levels.
“This is what we were seeing in a 9-month old Pre-Empt pond vs. a 2-month old Pre-Empt pond. A lot of nutrients have accumulated in the 9-month pond and are approaching the recommended nutrient levels that would be found in a conventional fertilizer system. Organic fertilizers like Pre-Empt don’t have a lot of magnesium in them. However, when the fertilizer is run in a pond system for 9 months the magnesium level rises and approaches what would be considered a conventional fertilizer target level for magnesium.”
Aging of the fertilizer solution also has had an impact on the root growth of the crops.
“When we compare how the roots look visually in the 9-month solution vs. the 2-month solution, the roots in the 9-month solution look much healthier,”Baras said. “The roots are very white, are longer and look really healthy and well-developed. There are also more roots on plants in the 9-month system.
“The root color is also significantly different. In the 2-month solution the roots look healthy, but there is some browning. They don’t have that crisp white look.”
Rethinking optimum pH levels
Baras said he has been able to produce healthy crops in a pH range from as low as 4 up to 6.5.
“For hydroponic leafy greens the recommended pH ranges from 5.5 to 6.5,” he said. “We have basil and butterhead lettuce growing very well in organic systems at a pH of 4. On the other side of the pH range, I’ve heard of aquaponic growers growing these crops at a pH up to 7 without any problems. Based on our trial results some of the conventional recommendations for hydroponics for both pH and nutrient levels might need to be revisited.
“One of the biggest issues I see with hydroponic growers is overcompensating. For instance, they feel that they need to be constantly watching the pH. They may set up monitoring and dosing systems to ensure the pH doesn’t go below 6 or 5.5. They are investing in extra equipment because they think they need to keep the pH precisely in this range. It may be a case that the plants will do well outside this range.”
Impact on crop timing
Baras said one factor that could affect the optimum pH and nutrient range is the light level.
“If a grower is providing supplemental light, then the optimum pH and nutrient range may be different,” he said. “With the trials we are conducting we aren’t that far off from what most hydroponic growers are targeting for growth rates. Thirty-five days is a target number for a lot of lettuce growers. We have done 35-day crops. We want to be able to grow an organic crop in the same amount of time as a crop grown with conventional fertilizers.”
For more: Hort Americas, (469) 532-2383; email@example.com; https://hortamericas.com.
David Kuack is a freelance writer in Fort Worth, Texas; firstname.lastname@example.org.
Tour of Hort Americas research and demonstration greenhouse in Dallas will show growers different hydroponic production systems for various vegetable crops.
Growers of hydroponic vegetables or those considering starting growing vegetables hydroponically should plan on attending the AmericanHort Production Technology Conference. Scheduled for Oct. 9-11 in Dallas, the conference begins with a Technology in Action Tour on Oct. 9 which will visit three local production operations: Hort Americas research and demonstration greenhouse, Seville Farms and Southwest Nursery.
All things hydroponic
Hort Americas, a horticulture and agriculture wholesale supply company, has retrofitted a 12,000-square-foot floriculture greenhousefor the hydroponic production of vegetable crops. Tyler Baras, who is the special projects manager at Hort Americas, is overseeing the trialing of five different production systems along with the testing of potential products for the company’s online catalog. The production systems include: nutrient film technique (NFT), deep water culture floating raft, a vertical hydroponic tower system, a flood-and-drain vertical rack system and a new capillary mat manufactured in Europe. The greenhouseis being used to grow a wide variety of lettuces, leafy greens, herbs and microgreens.
The NFT system uses a new channel design. Baras said the narrower channels allow for the aging of crops without having to physically move plants from nursery channels to finishing channels.
Hort America’s main floating raft deep water system is an in-house custom design that measures 32-feet by 28-feet.
“We have tried using a Venturi system to incorporate oxygen, but for the last two months we have been doing trials with compressed liquid oxygen,” Baras said. “We have been doing trials to see how plants respond to increased levels of dissolved oxygen. This deep water system hasn’t been flushed in over a year.
“We have been managing the nutrient solution with water tests and individual salts. Instead of using a standard N-P-K fertilizer like we have been using in the other production systems, we have really focused on water tests and making nutrient adjustments based on those tests. We have been trying to keep the nutrients within a target range and trying to run the system for as long as possible without having to flush any of the nutrient system. We are testing for all of the essential nutrients. We are also looking at sodium chloride levels and seeing how those accumulate. Also, we are tracking what essential nutrients accumulate over time and how we can adjust the fertilizer being added to accommodate the natural accumulation in the system.”
Baras is also studying how the water source can contribute to the nutrient level.
“We are considering how source water may be a limitation to applying this no-flush technique,” he said. “Our source water is municipal water, but it has a high sulfur content of about 44 parts per million. So we are looking at cutting out all sulfur inputs. We are learning the challenges of trying to manage a no flush system.”
In addition to the main deep water system, Baras said tour attendees will also see several smaller deep water culture systems.
“In these smaller deep water culture systems we will be showing the use of three different organic fertilizers where we are comparing the growth between them,” he said. “We will also be showing a smaller scale deep water culture system receiving aeration compared to one with no aeration.”
Vertical production systems
Another hydroponic system that Baras is working with is a vertical tower commonly used by smaller growers.
“We have a lot of customers who use this system so we decided to install one in the greenhouse so we could look at some of the issues that they are dealing with,” he said. “We also were looking to answer some of the questions that our customers had about using the system. An example is can this system be used to grow organically? We’ve done both organic and conventional trials with this system.
“We’ve also been looking at what crops perform best in this vertical system. We’ve done a lot of variety trials as well as with the other systems we’ve installed.”
Hort Americas is also trialing a vertical Growrack from Growtainer.
“This is a flood-and-drain vertical rack system,” Baras said. “The rack has three levels, but it could be expanded. The rack has a 2-foot by 5-foot footprint. We have equipped it with GE LED lights. This would be the type of system used in a vertical farm setup.”
Baras said the Growrack system, which is set up in the greenhouse, has done well in warm conditions because its water reservoir is below the rack.
“The reservoir is usually stored underneath the racks so it is in shade,” he said. “The water isn’t always in the trays so it doesn’t collect the heat from the trays. It works well in warm climates.”
Although Baras has grown full size crops in the Growrack, it is being used now primarily for seedling propagation.
“The focus of the system is how it has enabled us to cut back on the amount of space that is needed for propagation,” he said. “We can easily grow enough seedlings in this system for a 10,000-square foot greenhouse.
“The system is also being used by a Central Market store in Dallas to finish crops for its Growtainer farm. We helped consult on the management of the system and showed store officials how it could grow crops from start to finish in the same Growracks. The store is growing fully mature butterhead lettuce and basil in the system. This system can definitely work in indoor vertical farms.”
Baras said he has grown both organically and conventionally with the Growrack system.
In addition to trialing LED lights vs. natural light for greenhouse seedling propagation and crop staging, Baras said he is also looking at using LEDs supplemental light throughout the production of butterhead lettuce in the floating raft system.
“We are looking at how LED light affects leaf texture and plant morphology of butterhead lettuce,” he said. We are trying supplemental lighting during the summer. We are pulling shade so the light isn’t very intense. It appears that intense light can lead to tip burn that damages the plants leading to a poor quality crop. So we pull shade cloth and then run a prototype high-output LED grow light provided by GE for almost 20 hours. We deliver a low intensity of light over a longer period so we can provide the plants the light they need without stressing them. We are trying to improve the quality by adding LED light in order to produce more compact growth that is associated with LEDs.
“Under greenhouse shade cloth the lettuce leaves look fragile. We are trying to grow the lettuce to hit a certain weight. If the plants are grown under shade they look fairly large and floppy and the head doesn’t have the right density at its core. By using the LEDs we can produce the more traditional morphology where the plants have a dense core. The leaves aren’t floppy and the plants look more like traditional butterhead should look.”
Matching plants and production systems
Baras said he is trialing a wide range of crops in all of the production systems he is using.
“Primarily we are focused on lettuce and basil, but we are trialing a lot of varieties,” he said. “We definitely see some systems are capable of growing some varieties that other systems are not. We want to be able to recommend what varieties grow best in what systems. We are preparing a book based on our research that will include an entire section on strategies for how to use these production systems. We will provide example situations in the book discussing location, climate, market, what crops are being requested by that market and how to use that information to determine what production system is most appropriate.
“We are looking at primarily butterhead, romaine and oakleaf lettuce and 20 different basil varieties. We are also doing trials with arugula, spinach, cilantro, kale, chard, Asian greens and microgreens. We are doing an extensive study of herb varieties. There are also some unusual crops like stevia, wasabi arugula, celeriac and sorrel. We are determining all of these plants growth habits in the different production systems. This information will be in the book along with the details and nuances of growing each crop.”
Based on the trial results, Baras said the book will provide details on each plant variety and its performance in each system.
“The book will provide information on the growth a grower should expect in different environments based on the amount of light and temperature,” he said. “The book will offer projected production numbers a grower should be able to reach. These will be realistic targets for each of the production systems we have studied.”
How quickly hydroponically-grown lettuce and leafy greens seedlings are transplanted and their exposure to LED light during propagation can impact crop production times.
Most growers using traditional hydroponic substrates transplant lettuce and leafy greens seedlings as soon as the roots reach the bottom of the plugs. This usually takes from seven to 10 days.
“We are trying to see if we can go far longer in Stage 1, which is this seedling stage,” said Tyler Baras, special projects manager at Hort Americas in Bedford, Texas. “Stage 1 occurs in a propagation area.
“Some growers incorporate an intermediate phase (Stage 2) which is a growing out stage. Stage 2 might consist of nutrient film technique (NFT) channels closely spaced next to each other or a deep water raft system with high density spacing. Generally a 2-foot-by-4-foot raft holds 72 plants or more. Both Stage 2 and 3 occur in the final growing out system. During Stage 3 those same NFT channels are spaced further apart or in a deep water system the plants in a 72-count raft are transplanted to a lower density 28- or 18-count raft.”
Baras said holding the seedlings in Stage 1 for a longer period would reduce the amount of time that is required in the final Stage 3.
“This would actually be a two-stage system with an increase in time the seedlings are in the propagation stage or Stage 1,” he said. “Our reason for doing these studies is to see if we can eliminate the labor required to transplant the plants from Stage 2 to Stage 3, but still achieve yields similar to three-stage systems. Three-stage systems generally achieve more crop turns per year than two-stage systems. For many small growers trying to find enough labor and high labor costs can be major issues. If we can reduce the amount of labor required by extending Stage 1 this could help growers.”
Baras said the reason most growers don’t try to grow the seedlings longer during Stage 1 is the chance for root damage that can occur when the plugs are transplanted into the final production system.
“If seedlings are held too long, especially in a sheet substrate where there isn’t any divider between the plants, the roots can easily grow into the neighboring plugs,” he said. “When a grower goes to transplant the plugs and tries to pull them apart damage can be done to the roots. When the plugs are transplanted into the final system this root damage can lead to stunting and leaf dieback. The damaged leaves are more susceptible to disease pathogens and can attract fungus gnats. The plants will also require additional cleaning at harvesting to remove damaged leaves.”
Baras has observed the problems caused by holding the plugs longer in Stage 1 occur more often with transplanting into NFT systems than with deep water raft culture.
Baras said that he has conducted several trials with different substrates holding the seedlings in Stage 1 up to six weeks.
“We have gone the longest with self-contained plugs,” he said. “This is usually with organic production where there is slower growth. We have pushed the seedlings for a longer period of time. So far the best results with conventional hydroponic production are at about three weeks. With organic production it’s around four weeks because the plugs are self-contained and the roots don’t grow into neighboring plugs.
“We are pushing some of the seedlings to nearly a month and not seeing significant leaf dieback or stunting from root damage. We are shaving off several weeks within the final production system. It’s still possible to damage the seedlings if they are held in Stage 1. We are seeing the upper limit is higher for deep water culture than it is for NFT.”
Impact of LED lighting
Baras said another factor that can impact seedling development is exposure to supplemental light.
“We have been trialing different photoperiods and light intensities,” he said. “We have found that the light treatments that we give the seedlings can actually affect whether the plants produce more roots or more leaves. We are looking at the differences between exposing the seedlings to sunlight and LED light from GE Arize Lynk fixtures and different photoperiods.
“Depending on the lighting treatment we can create a smaller plant on top but increase root mass. This allows us to grow the seedlings longer without the plant canopies growing into each other. When the seedlings are removed for transplanting there is no damage to the leaves. There are more leaves left intact by growing more compact plants. We are still able to get a lot of root development.”
One of the most exciting findings that Baras is seeing is the increase in final weight of lettuce given LED supplemental light.
“When we started our research we were using traditional production methods,” he said. “We would sow the butterhead lettuce seed and place the trays under sunlight and then transplant the seedlings between seven to 14 days. With this traditional growing method we would produce a 6-ounce head. With the adjustments that we are making to staging and using LED lighting we are producing 8-ounce heads in the same amount of time. We are very excited about that. We think it is one of the most significant things coming out of our research greenhouse right now.
“The plants grown with LED light are finishing with 2 ounces more of plant weight. This seems to be related more to light quality and the influence that it has on the seedlings’ morphology than on total light received. It is not like the plants are receiving a lot more light when they are exposed to LEDs instead of sunlight. The morphology of the plants is completely different because of the light quality spectrum they are receiving. We now want to look further at light quality treatments during the seedling stage. This includes different ratios of blue/red LEDs, the inclusion of different colors and checking for variety specific results. There are still a lot of trials to do.”
One of the trials that Baras wants to study further is varying the length of time the lights are on.
“We are also looking at how long the lights are on,” he said. “Whether there is a big difference depending on the length of the photoperiod. We have not found an optimum length of time. We have found that more light is not always better.
“We are looking at exposing the seedlings to 20 hours or 24 hours of light. Right now 20 hours of light is outperforming 24 hours of light. But 24 hours of light is outperforming natural sunlight. This is across all crops, including a couple varieties of lettuce and Italian basil.”
For more: Hort Americas, (469) 532-2383; https://hortamericas.com.
David Kuack is a freelance technical writer in Fort Worth, Texas; email@example.com.
Researchers at Michigan State University used LED lights to produce compact flower and tomato seedling plugs.
By David Kuack
Growers and researchers are studying the effects that specific light wavelengths can have on ornamental and edible crops. Research studies are focusing on the effect light wavelengths can have on a variety of plant processes including growth, flowering, fruiting and postharvest quality.
Michigan State University horticulture professor Erik Runkle and former graduate student, now floriculture/nursery production extension educator Heidi Wollaeger studied the impact the ratio of red to blue light can have on the production of annual bedding plant seedlings. They looked at the effects of red and blue light on impatiens, petunia, salvia and tomato plugs.
Michigan State University floriculture/nursery production
extension educator Heidi Wollaeger and horticulture
professor Erik Runkle studied the impact that red and
blue light can have on bedding plant seedlings. Photos courtesy of Heidi Wollaeger, Mich. St. Univ. Ext.
“These four species are very common bedding plants for U.S. growers,” said Wollaeger. “They are key crops for their sales. The tomato plugs were being grown as vegetable transplants and not for production as greenhouse tomatoes for fruiting.
“We have also used these four species in other lighting trials that we have done recently. We wanted to be able to extrapolate from one study to another. In previous studies we looked at green light and the ratios of blue, green and red light.”
Seed was sown into 128-cell plug trays at a commercial propagator and moved into a large growth chamber at the university within two days where LED and fluorescent light treatments began immediately. The plants were Stage 2 plugs when the light treatments began. The seedlings had cotyledons and no true leaves. They were under the light treatments throughout the entire duration of the study.
The bedding plant plugs were grown in a growth chamber equipped with six individual LED chambers. The plugs grown under fluorescent lamps were grown in a separate growth chamber.
For all light treatments, plants were exposed to 160 micromoles per square meter per second (µmol·m−2·s–1) for 18 hours a day.
Plug trays of impatiens, petunia, salvia
and tomato were grown in a large growth
chamber at Michigan State where they
received LED or fluorescent light treatments.
“We chose 10 moles per day because that is a suggested light integral for most plants to be of at least moderate quality,” Wollaeger said.
“We didn’t want to deliver a light intensity much greater because as the intensity increases so does the light installation cost as well as the energy costs to run the lamps. We were implementing a practical light level for growers.”
Wollaeger said the study was terminated after four to five weeks because at that time the plants were ready for a commercial grower to transplant.
“This study simulated what growers would actually do in their facilities if they were to install a sole light source LED chamber,” she said. “They would use this high value propagation space to produce the propagules and then transplant them and put them into the greenhouse. These could be used by growers who are finishing the plants themselves or by a propagator who is selling the plugs to other growers.”
Light effects on bedding plants
Wollaeger said all of the species grown under the red light dominant background with at least 10 µmol·m−2·s–1 of blue light displayed desirable plant growth responses.
“These plants showed compact growth, thicker leaves and thicker stems,” she said. “As a general rule of thumb, growers should provide at least 10 µmol·m−2·s–1 of blue light if they are providing
a red dominant environment to increase plant quality, which results in compact, well-branched growth.
“This treatment might reduce the need for plant growth retardants. If the light environment is being altered to include more blue light in a sole-source environment, stem elongation is reduced. This will depend on the crop. Every crop has a different vigor depending on the species and cultivar. This study only looked at four commercially important species.”
Four bedding plant species, including tomato, grown
under a red light dominant background and under at
least 10 µmol·m−2·s–1 of blue light
displayed desirable plant growth responses, including compact growth,
thicker leaves and thicker stems.
Plants grown under the fluorescent lamps usually produced the most chlorophyll, but also had the thinnest leaves. Impatiens and salvia had greater fresh shoot weight when exposed to treatments without blue light than with at least 80 µmol·m−2·s–1 of blue light.
Impatiens grown under a high proportion of blue light developed more flower buds. Wollaeger said whether this early flowering is a negative or positive effect depends on the plug cell size.
Impatiens grown under a high proportion of blue light
developed more flower buds than
plants provided with mostly red light.
“If the plants are being grown in a small plug size like a 288 cell and will be transplanted into large finished containers, it might not be desirable for early bud development,” she said. “The formation of flower buds could impact the rooting of the plants, but that depends on the cell pack size. If a grower is transplanting the plugs directly into smaller containers, he might want earlier flowering.”
Reduction of tomato intumescences
A benefit of growing tomato plugs under high blue light levels and fluorescent lamps was the reduced incidence of leaf intumescences (sometimes called edema), which are small protrusions that form on leaves, stems and petioles. Wollaeger said this physiological disorder has been associated with a lack of ultraviolet light or blue light.
“This physiological disorder is cultivar specific,” she said. “Some cultivars are more prone to developing this disorder compared to others. ‘Early Girl’ is the cultivar that we used and it did develop intumescences under treatments with small amounts of blue light.”
More greenhouse research
This particular research study did not look at the effects of the light treatments after plants are moved into the greenhouse.
Wollaeger said Dr. Runkle’s lab is currently conducting another study to determine the lasting effect of light treatments on transplanted plugs.
“Whether or not a light treatment has any lasting effect once the propagules are transplanted and placed in the greenhouse is going to depend on the light environment in the finishing location,” she said. “If the daily light integral is at least 10 mol·m−2·d–1 during the plug stage, there is probably going to be some height suppression when the plants are finished in the greenhouse. I wouldn’t expect there would be a major lasting effect of stem elongation suppression once in the greenhouse.”
Not alot of time for a post today, but wanted to put a teaser out there that we are looking at an organic fertilizer that should fit well with Hydroponically Grown Greenhouse Greens, Herbs and Veggies.