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Nutrient guidelines for hydroponic tomato production

By Victor Loaiza, on behalf of Hort Americas

It is important to conduct water and nutrient solution analyses on a regular basis to ensure hydroponic tomatoes are receiving the proper level of nutrients.

Making sure that hydroponically-grown tomatoes receive the proper nutrient levels requires testing water and nutrient solutions. Growers also need to confirm that irrigation equipment is delivering the correct amount of fertilizer. Nutrient levels should be monitored and adjusted according to the crop developmental stage, the season, light levels and tomato type.

“In applying fertilizer to a plant grown either in soil or in a soilless medium, the goal is to match the nutrient uptake of the crop as closely as possible to the amount provided as fertilizer” (Mary Peet, USDA, Division of Plant Systems-Production, 2005). There are many reasons to do so, but a very important reason is to prevent fertilizer runoff which is actually money runoff.” For growers with open irrigation system this will hurt the most. In a closed irrigation system, excess fertilizer is recovered and recycled after water treatment.

Water sample analysis

It’s very important to regularly conduct irrigation water and nutrient solution (water + fertilizers) analyses. Irrigation water quality from a well, dam or municipal system should be determined before implementing any type of fertilization plan. Important levels growers should know include: water electrical conductivity (EC), water pH, sodium (Na), chloride (Cl) if using a municipal water source, calcium (Ca), magnesium (Mg) and sulfates (SO4). The preference is for low levels of all these elements. Water EC less than 0.5 millisiemens/centimeter (mS/cm) is a good level. If the water pH is high, a pretreatment can be done with sulfuric acid, phosphoric acid or citric acid. Optimum and safe pH levels are between 5 and 6.

Nutrient solution sampling should be conducted on a weekly or biweekly basis. Nutrient solution sampling should be taken from two sources:

1. Feed is the nutrient solution the irrigation system is pumping to the plants sampled at the dripper.

2. Drain is the leachate coming from the substrate. This is critical to a fertilization strategy.

Useful information

The information obtained from the nutrient solution analysis helps to:

1. Verify the irrigation equipment is dosing the correct amount of fertilizer.

2. Verify the EC and pH of the nutrient solution are satisfactory levels.

3. Determine the amount of fertilizer by element being absorbed by the plants.

4. Determine the amount of fertilizer that needs to be added/subtracted from the nutrient solution.

It can be determined if the amount of irrigation is appropriate by looking at the drain EC. If the EC is too high, there may not be enough water being applied to the plants. If the EC is too low (lower than the feed EC) plants may be receiving too much water.

5. Verify if the amount of irrigation is appropriate by looking at the drain EC. If the EC is too high, there may not be enough water being applied to the plants. If the EC is too low (lower than the feed EC), plants may be receiving too much water.

There are many laboratories that perform this type of water and nutrient solution analysis. It is important to choose a lab where the staff has experience in hydroponics.

Two recommended laboratories are Groen Agro Control in the Netherlands and Perry Laboratory in Watsonville, Calif.

Recommended nutrient levels

A Netafim fertilizer controller unit

In the photo of the Netafim crop management technology fertilizer dosing unit, the blue line on the left is the irrigation water (well water or municipal water with no fertilizer). This water is pumped to the mixing chamber where fertilizers are injected and the water becomes the nutrient solution (pink line on the right). The nutrient solution flows through EC and pH sensors to make sure that the target EC and pH are maintained.

Table 1 shows the nutrient levels by element or molecule recommended for tomato nutrient solutions measured at the drain. Elemental levels at the lower or higher margins are not necessarily bad. Maintaining the proper nutrient level is crop dependent.

Table 1. Nutrient solution elements in drain water

Table 1 reflects the desired values obtained by a drain sample analysis. By constantly analyzing the nutrient solution, the target levels can be matched that best suits the crop.

Preparing nutrient solutions

The most common chemicals for mixing nutrient solutions are mentioned in the Hort Americas article on hydroponic greenhouse pepper production.

They include:

  • Ca(NO3)2 (Calcium nitrate)
  • KNO3 (Potassium nitrate)
  • KH2PO4 (Mono-potassium phosphate)
  • MgSO4*7 H2O (Magnesium sulfate)
  • H3BO3 (Boric acid)
  • MnCl2*4 H2O (Manganous chloride)
  • CuCl2*2 H2O (Cupric chloride)
  • K2SO4 (Potassium sulfate)
  • MoO3 (Molybdenum trioxide)
  • ZnSO4*7 H2O (Zinc sulfate)
  • Fe Sequestrene 330 (iron chelate)

General recommendations

  • Some tomato varieties are more susceptible to blossom end rot (BER) than others. Check irrigation strategy and nitrate levels since high nitrates could be the cause of BER.
  • Keep daily irrigation measurements in a logbook (EC, pH and drain percentage). This is a daily task that should be performed early in the morning before the irrigation cycles start. See handheld EC/pH meters
  • Compare the manual EC/pH readings with the irrigation unit readings, they should match.
  • Keep K:Ca ratio close.
  • Calibrate pH and EC meters once a week.
  • Calibrate pH sensors on the irrigation unit at least once a month.
  • Keep the irrigation system clean and flush it periodically.
  • Clean fertilizer tanks every month to avoid fertilizer sedimentation.
  • Keep the pH of the micronutrient stock tank low (pH 4).



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


Here are some of the fertilizers Hort Americas offers:


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Pre-Empt FAQ


We have been receiving a lot of questions about Pre-Empt. He are some responses to the common questions:


When is Pre-Empt appropriate?

It is best suited for recirculating hydroponic production of leafy greens. It can be used as a direct substitute for conventional fertilizers in NFT, DWC/Floating Raft, and Flood & Drain. When used properly, it won’t clog 1/4″ emitters which is very rare for an organic fertilizer.

When is Pre-Empt not appropriate?

The cost may be prohibitive for drain-to-waste systems. We do not have any experience with the product being used in aeroponic or aquaponic systems.

Can Pre-Empt be used for tomatoes?

Yes, but…
-Growth may be overly vegetative and not as reproductive as standard commercial tomato formulas
-Blossom end rot will likely be an issue on larger varieties like beefsteaks
-Works well with grape and cherry tomatoes but still may have overly vegetative growth
-Calcium may be supplemented with an organic solution grade gypsum

What amendments would you suggest to use with Pre-Empt?

-Organic solution grade gypsum and silica may be used to reduce tip burn or blossom end rot
-Inoculants like TerraBella can help reduce biofilms and improve nutrient availability

How do I inoculate a tank with beneficial microbes?

Fill a 5 gallon bucket with water and add 1 oz molasses. Let water sit for 1 day to remove chlorine (unless using RO or distilled water). Add 2 oz. of TerraBella and let sit for 1 day before adding to reservoir. This is enough to inoculated 300 gallons of nutrient solution.

How often should I change the reservoir?

This is going to vary a lot depending on growing environment, system, water source, and fertilizer rate. In general, using a water source with a very low EC and keeping the fertilizer rate low will help extend the life of the reservoir. Some growers flush their system once every 4-5 months and some growers flush every two weeks. The cost to build a reservoir with Pre-Empt may be up to 100x more expensive than conventional fertilizers so it is very important to reduce the frequency of flushes.

What EC should I maintain?

This will depend on source water EC and crop. The target EC is generally going to be lower than the EC used with conventional fertilizers. Generally leafy greens are grown at an EC ranging from .8 up to 1.6. It is best to start low to avoid the development of biofilms in the system

What pH should I maintain? And how?

I’ve seen growers completely ignore pH while using Pre-Empt. The pH may fluctuate from 4.8 up to 7.5 without noticeable effect on the crop. I’ve also seen growers maintain pH levels with citric acid and sodium bicarbonate.

How consistent is Pre-Empt from batch to batch?

There is variability in the product and it is possible that a batch may perform differently than previous batches. This variability is generally minimal enough that growers do not need to adjust practices.

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Pre-Empt Organic Hydroponic Nutrients


Proudly brought to the commercial hydroponic and organic grower by Hort Americas and specifically developed for recirculating nutrient film technique (NFT), the Pre-Empt Hydroponic Nutrient is packed with the essential micro- and macro-nutrients, amino acids and vitamins plants hunger for!

Pre-Empt goes through a five stage fermentation process which is above and beyond other products by incorporating molasses with other natural plant extracts. This process packs Pre-Empt with essential macro-nutrients, micro-nutrients, amino acids like humic and fulvic acid, as well as an array of vitamins which build a full spectrum of nutrients that plants desire.

  • Excellent for lettuces, basil, leafy greens and culinary herbs

  • OMRI-listed

  • We suggest pairing with Terra Bella to naturally promote the uptake of nitrogen and other essential nutrients for plant health. The combination of aerobic and anaerobic microbes works throughout the root zone to increase crop yield and resistance to disease and pests.

  • For further resources including a quick video and Organic Fertilizer Programs, click here!

Pre-Empt can be used in conjunction with a solution grade organic gypsum (calcium sulfate) and magnesium sulfate.


Hort Americas is an innovative leader in North America’s controlled environment agriculture industry (CEA) and strives to continually innovate in agriculture via premium technical support, professional salesmanship, unmatched customer service and outstanding products to our customers in the United States, Canada, Mexico, and the Caribbean.

For questions and support, click here!

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Solving the Hydroponic Fertilizer Equation


Hort Americas Hydroponic Fertilizer

It is quite common for both start-up and experienced commercial hydroponic growers to feel they need a math degree when it comes to calculating the necessary micro and macro elements of their water soluble fertilizer. Hort Americas has solved the equation with their specially formulated 9-7-37 Hydroponic Fertilizer.  Hort Americas has developed this unique fertilizer in cooperation with CEA hydroponic specialists, academicians and researchers to meet the nutritional needs of crops produced by hydroponic leafy green growers.

  • Designed for leafy greens, culinary herbs, micro greens and other crops grown hydroponically
  • Can be used as a constant feed or as a supplement
  • Delivers essential nutrients for efficient uptake by the root system
  • Unique TPA (Thermal Poly Aspartic Acid) additive which enhances the plants ability to uptake phosphorus
  • To assist the grower even further, Hort Americas has developed a helpful hydroponic fertilizer calculator within part 3 of a 3-part instruction video series found on the Hort Americas website


Hort Americas recommends the grower have their source water tested by a professional water analysis laboratory to determine the macro and micro nutrient levels, pH, EC and total alkalinity before assessing appropriate rates for their fertilizers.

Hort Americas is an innovative leader in North America’s controlled environment agriculture industry (CEA) and strives to continually innovate in agriculture via premium technical support, professional salesmanship, unmatched customer service and outstanding products to our customers in the United States, Canada, Mexico and the Caribbean.

For questions, support or to purchase → Click Here!

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Where does phosphorus fertilizer come from?

Phosphorus symbolIf your phosphorus fertilizer is sourced from the U.S. it is probably derived from Hillsborough, Polk, Manatee, and Hardee counties in Florida. Recently, I had the opportunity to tour Mosaic’s South Fort Meade Mine facility. The Mosaic Company’s South Fort Meade Mine has an annual production of 6.5 million tons per year running 24/7/365. It’s size is 28,000 total acres with 15,000 currently active acres with 3 drag lines.

Process Overview: Three Steps

1. Mining – Phosphate matrix is extracted from the ground. Clay and sand are removed. The refined phosphate rock is transported by rail for further processing.

2. Fertilizer production – Mosaic process nutrients in the phosphate rock into a water soluble form suitable for plant uptake

3. Distribution – Finished fertilizer is distributed both domestically and internationally by ship, barge, rail and truck directly to growers.

The massive production draglines are massive excavators (Fig. 1) that actually can move slowly across the mine dragging an oversized bucket. The Production Draglines are manned by just two employees. Each of the draglines weigh 6.9 million pounds and the bucket alone weighs 100,000 lbs (Fig. 2). The mining cut can be up to 320’ (Fig. 3). The overburden (sand & clay) is first removed to uncover the matrix of phosphate rock, sand and clay. The matrix is removed until it reaches hardrock (limestone or dense clay). If you are lucky enough you can discover prehistoric shark teeth or bones from creatures that once ruled the ocean where the mine is today.

Pit cars deliver water hydraulically with 300 psi and 16,000 gym to churn the matrix into a thick slurry that can be pumped back to the plant. At the plant, the washer removes oversized material between 1- 8 inches. Clay is scrubbed and rinsed away where it is moved to the clay reclamation centers. The washer feeds all undersized phosphate and sand smaller that 1mm to the Flotation Plant for separation. A biodegradable soap from pine trees is used to separate the phosphate from the sand. The sand is used to reclaim the mine. Since 1975 all mined land is reclaimed acre for acre (Fig. 4).

The phosphate rock is then loaded and shipped to fertilizer plants all over the US and then it eventually ends up in your hands where you use it grow healthy plants.

Special thanks to Mosaic company and the American Society for Horticulture Science for offering this unique tour.

ASHA logo Mosaic logo


Figure 1. Production Draglines w bucket
Figure 1. Production Draglines w bucket


Figure 2. Dragline bucket
Figure 2. Dragline bucket


Figure 3. Mining cut
Figure 3. Mining cut


Figure 4. Park at reclaimed mine
Figure 4. Park at reclaimed mine



Further reading:

Mosaic, South Fort Meade mine’47.5%22N+81%C2%B045’25.9%22W/


The Fertilizer Institute.