Comparing Nutrient Solutions for Hydroponic Tomatoes

When growing tomatoes hydroponically, one of the most critical decisions you’ll make is choosing the right nutrient solution. The composition of your nutrient solution can dramatically affect both the quantity and quality of your harvest. In this post, I’ll examine different nutrient formulations that have been tested in scientific studies and discuss how they impact tomato production in soilless systems.

Picture of a soilless tomato greenhouse

Understanding Nutrient Solution Basics

Before diving into specific formulations, it’s important to understand that tomato plants have changing nutritional needs throughout their growth cycle. Research has shown that early in the season, excessive nitrogen can cause plants to become too vegetative, resulting in bullish growth that produces misshapen fruits and increases susceptibility to disease (1). High potassium levels can also create problems by interfering with calcium and magnesium absorption, leading to blossom end rot.

Most successful nutrient programs divide the growing season into distinct stages. The seedling stage requires lower concentrations of nutrients, particularly nitrogen, while mature fruiting plants need substantially higher levels of most nutrients to support both vegetative growth and fruit development (2).

Comparing Two Common Formulations

Research has established several effective nutrient formulations for hydroponic tomatoes. I’ll compare two well documented approaches that represent different philosophies in nutrient management.

Nutrient Arizona Formula (Seedling) Arizona Formula (Fruiting) Florida Formula (Early) Florida Formula (Late)
Nitrogen (N) 113 ppm 144 ppm 60 to 70 ppm 150 to 200 ppm
Phosphorus (P) 62 ppm 62 ppm 39 ppm 39 ppm
Potassium (K) 199 ppm 199 ppm 200 ppm 300 to 400 ppm
Calcium (Ca) 122 ppm 165 ppm 150 to 200 ppm 150 to 200 ppm
Magnesium (Mg) 50 ppm 50 ppm 48 ppm 48 ppm

The Arizona formulation (2) maintains relatively consistent macronutrient levels between growth stages, with only modest increases in nitrogen and calcium as plants mature. In contrast, the Florida approach (1) uses much lower nitrogen during early growth to prevent bullishness, then dramatically increases both nitrogen and potassium during fruit production.

Micronutrient Requirements

While macronutrients often receive the most attention, micronutrients are equally essential for healthy tomato production. These elements remain fairly constant throughout the growing cycle (2). Standard micronutrient concentrations for hydroponically grown tomatoes include iron at 2.5 ppm, manganese at 0.62 ppm, boron at 0.44 ppm, zinc at 0.09 ppm, copper at 0.05 ppm, and molybdenum at 0.06 ppm.

Micronutrient Concentration (ppm)
Iron (Fe) 2.5
Manganese (Mn) 0.62
Boron (B) 0.44
Zinc (Zn) 0.09
Copper (Cu) 0.05
Molybdenum (Mo) 0.06

The Impact of Nitrogen Supply on Quality

Research on nitrogen management has revealed some surprising findings. A study examining nitrogen supply at different growth stages found that increasing nitrogen from 140 to 225ppm during the vegetative stage increased protein, vitamin C, and sugar content in fruits (3). However, the effect on lycopene and beta-carotene depended heavily on the potassium supply during the reproductive stage.

Other research examining lower nitrogen levels has shown that minimal nitrogen supply can actually enhance lycopene content in tomato fruits, particularly when coupled with sufficient water supply (4). Studies in hydroponic culture have demonstrated that either the lowest or medium levels of nitrogen application produced the best lycopene content, suggesting that optimal nitrogen levels for antioxidant production may be lower than those for maximum yield.

Potassium’s Role in Fruit Quality

Potassium plays a fundamental role in determining tomato fruit quality. Research has demonstrated that increasing potassium supply during the reproductive stage significantly enhances sugar concentration, vitamin C content, protein levels, lycopene, and beta-carotene in tomato fruits (3). The effect is particularly pronounced when potassium levels increase from 200 to 500ppm.

Another comprehensive study found that high proportions of potassium in the nutrient solution increased quality attributes including fruit dry matter, total soluble solids content, and lycopene content (5). However, these same researchers found that high proportions of calcium improved tomato fruit yield and reduced the incidence of blossom end rot, highlighting the importance of balancing these two nutrients.

Electrical Conductivity Management

One of the most innovative approaches to nutrient management involves carefully controlling the electrical conductivity (EC) of the nutrient solution. A study in closed NFT (Nutrient Film Technique) systems examined three different EC replacement set points: 5, 7.5, and 10 mS/cm (6). Remarkably, the highest EC replacement set point produced yields equivalent to lower EC treatments while significantly improving fruit quality.

The higher EC replacement threshold resulted in better dry matter content and total soluble solids in berries. Additionally, it demonstrated superior environmental sustainability by reducing total nutrients discharged into the environment by 37% compared to the medium EC treatment and 59% compared to the low EC treatment (6). This approach challenges conventional thinking about salinity stress in tomato production.

Calcium Management and Blossom End Rot

Calcium nutrition presents one of the most common challenges in hydroponic tomato production. Blossom end rot, characterized by dark lesions on the blossom end of fruits, results from calcium deficiency in developing fruits. However, this deficiency often occurs even when calcium levels in the nutrient solution appear adequate (1).

The problem frequently stems from antagonism between nutrients. Excessive potassium in the nutrient solution can interfere with calcium uptake by plant roots. This is particularly problematic early in the season when using pre-mixed fertilizers that contain high potassium levels. Growers working with water containing less than 50 ppm calcium need to be especially cautious about potassium concentrations.

To minimize blossom end rot, it’s critical to maintain calcium levels between 150 and 200 ppm while keeping early season potassium levels moderate. Some growers supplement calcium nitrate with calcium chloride to increase calcium availability without adding more nitrogen. Each pound of calcium chloride (36% Ca) in 30 gallons of stock solution increases calcium concentration by approximately 14 ppm in the final nutrient solution when injected at a 1% rate (1).

Effects on Yield and Quality Parameters

The differences between nutrient formulations can significantly impact both yield and fruit quality. Research consistently shows that inadequate nitrogen during fruiting stages produces lower yields, though the fruits may have better sugar content and flavor. Conversely, excessive nitrogen can produce abundant foliage at the expense of fruit production (4).

Potassium levels have a pronounced effect on fruit quality parameters. Adequate potassium improves fruit firmness, color development, and sugar content (3). However, excessive potassium can lead to calcium and magnesium deficiencies that compromise both yield and quality.

The timing of nutrient adjustments also matters significantly. Studies have shown that gradually increasing nutrient concentrations as plants transition from vegetative to reproductive growth produces better results than sudden changes in formulation. Plants that experience consistent, appropriate nutrition throughout their lifecycle typically show improved yields and more uniform fruit quality (6).

Practical Considerations

When implementing a nutrient program, several practical factors deserve consideration. Water quality plays a fundamental role in determining how much of each nutrient to add. Wells in many regions naturally contain significant calcium and magnesium, sometimes providing 40 to 60 ppm calcium (1). These naturally occurring nutrients should be factored into your formulation calculations.

The pH of your nutrient solution also affects nutrient availability. Research has established that maintaining pH between 5.5 and 6.0 ensures optimal nutrient uptake (2). Water with high alkalinity requires acidification, which can be accomplished using phosphoric acid or sulfuric acid depending on your phosphorus requirements.

The type of hydroponic system you’re using may also influence your nutrient concentrations. Systems requiring fewer daily irrigation cycles may need higher nutrient concentrations to ensure plants receive adequate nutrition. The general principle is that nutrient concentrations should be higher in systems with less frequent fertigation compared to those with continuous or very frequent feeding (1).

Advanced Management: The Transpiration-Biomass Ratio

One of the most sophisticated approaches to nutrient management involves calculating a recovery solution based on the transpiration-biomass ratio (6). This method recognizes that the relationship between water use and dry matter production changes throughout the growing cycle.

Research has shown that the transpiration-biomass ratio is high early in the crop cycle (approximately 300 liters per kilogram of dry weight), decreases during mid-season to a relatively stable phase, and then increases again late in the season (up to 400 liters per kilogram). This pattern suggests that nutrient concentrations should be adjusted accordingly: lower concentrations in the first and last phases, and higher concentrations during the middle phase when biomass accumulation is most rapid.

Conclusion

Successful hydroponic tomato production requires careful attention to nutrient solution composition. While several proven formulations exist, the research clearly shows that no single approach works best for all situations. The Florida formulation with its conservative early nitrogen levels may be ideal for preventing bullishness in greenhouse production, while higher EC strategies can improve fruit quality in closed systems.

Key takeaways from the scientific literature include: maintain nitrogen between 60 and 70 ppm early in the season to prevent excessive vegetative growth, increase potassium substantially during fruiting to enhance quality parameters, keep calcium between 150 and 200 ppm throughout the season while monitoring potassium levels to prevent antagonism, and consider that higher EC values (up to even 10 mS/cm) may be feasible limits for nutrient solution replacement in recirculating systems.

Starting with a well researched base formulation and making careful adjustments based on plant response, tissue analysis, and your specific growing conditions provides the most reliable path to optimizing both yield and quality in your hydroponic tomato crop. The scientific evidence demonstrates that nutrient management is not a one-size-fits-all proposition, but rather a dynamic process that should respond to both plant developmental stage and environmental conditions.




pH vs Nutrient Availability: Rethinking the Classic Charts

If you’ve been around hydroponics long enough, you’ve probably seen the ubiquitous “pH vs nutrient availability” chart. It usually looks like a series of colored bars, each showing how available a nutrient supposedly is across a pH range. The bars are wide for some nutrients at certain pH values, narrow for others, and the chart often comes with a moral: keep your solution pH between 5.5 and 6.5.

I discussed some of these issues in a previous post, but it’s worth revisiting them here with a clearer chart. The problem is that most of these charts trace back to soil agronomy research from the 1930s and 1940s. They’re not based on solution chemistry relevant to hydroponics. They conflate microbial activity, lime chemistry, and plant physiology with solubility. And, in some cases, they are flat out misleading.

Let me talk about why the traditional chart is wrong, what modern chemistry tells us, and how a more honest representation looks.


Where the Old Charts Went Wrong

The historical diagrams were designed for soils, not hydroponic solutions. For example:

  • Nitrate (NO₃⁻): In many charts, nitrate availability appears to fall off at low pH. In reality, nitrate is completely soluble across any reasonable pH range. The “loss” in those charts comes from soil microbial nitrification shutting down under acidic conditions, not relevant when you’re directly dosing nitrate salts in solution.
  • Calcium (Ca) and Magnesium (Mg): Old charts show Ca and Mg as always available at high pH. But that ignores precipitation with phosphate or carbonate, which can start as low as pH 6.2 for Ca. The old charts show high Ca and Mg availability at high pH because the high pH in soils was usually achieved by the addition of dolomite or lime, which greatly increased Ca and Mg concentrations in soil, this is not the case in a soilless setup.
  • Micronutrients (Fe, Mn, Zn, Cu): These are shown as less available above neutral pH, which is true for unchelated forms (they hydrolyze and precipitate quickly). But in hydroponics, I typically use chelates, and their stability extends availability well above pH 7.
  • Phosphorus (P): Charts often suggest a broad plateau around pH 6 to 7. In truth, phosphate solubility is sharply influenced by calcium concentration and carbonate alkalinity. The idea of a universal “wide bar” is misleading.

These errors matter. They lead growers to overemphasize the magic 5.5 to 6.5 range without appreciating that different nutrients behave differently, and that chelation or precipitation risks can change the picture entirely.


Building a Better Chart

To improve on the old diagrams, I constructed a new heatmap. Instead of arbitrary bar widths, each nutrient’s relative availability (scaled from 0 = low to 1 = high) is modeled based on actual solubility, speciation, and chelation chemistry. The chart covers pH 4.0 to 8.5.

Updated chart I created for nutrient availability in soilless systems based on chemical and plant physiology principles

This chart is not an absolute quantitative prediction (real world systems have variations depending on concentration, alkalinity, chelate type, etc.). But it captures the directional chemistry more honestly. For nutrients that are effectively pH independent (like nitrate), the line is flat. For those that crash with pH (like unchelated iron), the line drops. And for Ca and Mg, I’ve introduced tapering to reflect phosphate precipitation behavior.


Nutrient by Nutrient Ranges

Here’s a summary table describing the approximate pH behavior, the range of best availability, and the underlying reason:

Nutrient Broad Availability Range Notes / Reason
NO₃⁻-N 4.0 to 8.5 Soluble across all relevant pH; uptake independent of pH in hydroponic solution. Old charts confused microbial nitrification with solubility.
NH₄⁺-N Best <6.5; declines >7.0 At higher pH, conversion to unionized NH₃ increases, which is less available and potentially toxic.
Phosphorus (P) Peak 5.5 to 6.5; drops <5.2 and >7.0 Solubility falls at high pH due to Ca+P precipitation (starting ~6.2); also limited at low pH by fixation and speciation.
Potassium (K) 4.0 to 8.5 Monovalent cation, highly soluble, minimal precipitation issues (sometimes K containing silicates at higher pH values)
Calcium (Ca) Stable <6.0; declining >6.2 Precipitates with phosphate and carbonate as pH rises; availability falls gradually above ~6.2.
Magnesium (Mg) Stable <6.5; mild decline >7.0 Mg+P precipitation is less aggressive than Ca+P; solubility loss is slower but still possible at higher pH.
Sulfate (SO₄²⁻) Broad 4.5 to 8.0 Generally soluble. At very low pH, some soils can adsorb sulfate due to protonated variable charge surfaces, reducing availability. At very high pH, reduced root uptake efficiency and competition with other anions can occur; in concentrated Ca²⁺ + SO₄²⁻ systems gypsum may precipitate by saturation.
Iron (Fe, unchelated) Max <5.5; falls sharply >6.0 Fe³⁺ hydrolyzes and precipitates as hydroxides and oxides above ~pH 6; nearly unavailable by pH 7.
Manganese (Mn, unchelated) Best <6.0; declining >6.3 Mn²⁺ oxidizes and precipitates above neutral pH.
Zinc (Zn, unchelated) Best <6.0; low >7.0 Zn²⁺ solubility decreases with increasing pH; precipitates as hydroxide/carbonate.
Copper (Cu, unchelated) Best <6.0; poor >7.0 Cu²⁺ strongly hydrolyzes, falls out of solution quickly with rising pH.
Boron (B) Best 5.5 to 6.8 Boric acid is readily available in this range; at higher pH, more borate forms, reducing uptake.
Molybdenum (Mo) Improves >6.0 Molybdate solubility increases with pH; plants often deficient in acidic conditions, more available at neutral/alkaline pH.

The Ca vs Mg Difference

A key improvement over older charts is distinguishing calcium from magnesium. While both can precipitate with phosphate, their behaviors differ:

  • Ca+P precipitation is strong and begins around pH 6.2, especially in solutions with 1 to 3 mM phosphate. Brushite, dicalcium phosphate, and hydroxyapatite phases progressively reduce solubility.
  • Mg+P precipitation is slower and less pronounced. Mg²⁺ is more strongly hydrated and less eager to form insoluble phosphates. It tends to stay soluble longer, only declining gently above pH 7.

Chelation: The Missing Dimension

My chart above shows unchelated forms. In real hydroponics, Fe, Mn, Zn, and Cu are almost always chelated. Depending on the chelate (EDTA, DTPA, EDDHA, HBED), stability can be maintained up to pH 7.5 to 9. This dramatically extends availability, particularly for Fe. A separate chart is needed to show chelated behavior.


Why This Matters

So why obsess about getting this chart right?

Because oversimplified charts lead to oversimplified thinking. If you believe nitrate solubility collapses below pH 6, you might panic when your reservoir drifts to 5.2, even though NO₃⁻ is unaffected. If you believe Ca is “always available,” you might miss that phosphate precipitation is happening in your tank right now at pH 6.3. And if you don’t distinguish between chelated and unchelated micronutrients, you’ll misdiagnose deficiencies.

A better chart isn’t just about scientific pedantry. It’s about helping growers make better decisions: when to acidify, when to buffer, when to choose a stronger chelate, and when to worry (or not worry) about a drifting pH.


Final Thoughts

The classic nutrient pH charts had their place in teaching basic agronomy 80 years ago. But hydroponics deserves more precision. Nutrients don’t all behave the same way. Some are flat across the entire range (NO₃⁻, K). Some rise or fall gradually (B, Mo, Mg). Others are brutally sensitive (Fe without chelates). And precipitation interactions mean that Ca and phosphate availability are tied together, not independent.

This new heatmap and the accompanying table aren’t the last word, they’re a more honest starting point. The real message is: understand the chemistry, not just the cartoon.




Can you manage downy mildew in hydroponic basil with organic foliar sprays?

Basil downy mildew, caused by the obligate oomycete Peronospora belbahrii, has become one of the most serious diseases affecting hydroponic and greenhouse basil production globally. The pathogen, first documented in Europe in 2001 and later detected in the United States in 2007, requires high relative humidity (at least 85%) or wet leaves to infect plants (1). Temperature preferences favor moderate conditions around 20°C rather than higher temperatures, which explains why the disease thrives in controlled environment systems where leaf wetness and humidity are difficult to manage (1).

Downy mildew in basil shows characteristic black marks on the underside of leaves

Understanding the infection process is critical for designing effective spray programs. Under conditions of continuous free moisture, sporangia germinate within 3 to 5 days by producing germ tubes that penetrate basil leaves directly through the epidermis, typically without entering through stomata (2). Seven days after initial infection, sporangiophores bearing new sporangia emerge through stomata on both the upper and lower leaf surfaces, creating secondary inoculum that spreads rapidly throughout greenhouse facilities (2). This relatively short cycle from infection to sporulation means that preventive measures must start before visible symptoms appear.

Multiple field trials evaluating organic fungicides have delivered sobering results for growers seeking alternatives to conventional chemistry. A comprehensive study testing products approved for organic production, including copper octanoate, hydrogen dioxide, sesame oil, neem oil, thyme oil, citric acid, Bacillus species, and Streptomyces lydicus, found that none were effective at controlling downy mildew when applied to susceptible basil cultivars (3). Applications were made weekly starting before symptom development, and efficacy was assessed based on incidence of symptomatic leaves rather than severity, reflecting the zero tolerance for disease on fresh market herbs (3). A summary of the tested fungicides and their effectiveness is shown on the following table.

Product (Active Ingredient) Mode of Action Effectiveness
Cueva (Copper octanoate) Contact fungicide, disrupts enzyme function Ineffective
OxiDate (Hydrogen dioxide) Oxidizing agent, contact action Ineffective
Organocide (Sesame oil) Physical barrier, suffocation Ineffective
Trilogy (Neem oil) Physical barrier, azadirachtin content Ineffective
Forticept EP #1 (Thyme oil) Essential oil, contact action Ineffective
Procidic (Citric acid) pH modulation, contact action Ineffective
Actinovate (Streptomyces lydicus) Biocontrol, competitive colonization Ineffective
Companion (Bacillus subtilis) Biocontrol, induced resistance Ineffective
Double Nickel (B. amyloliquefaciens) Biocontrol, antibiosis Ineffective
Regalia (Reynoutria sachalinensis) Plant defense activator Ineffective

The limited efficacy of organic fungicides appears related to the aggressive nature of the pathogen and the difficulty of achieving thorough foliar coverage in dense basil canopies. Even when combined with resistance inducers or natural products, organic treatments failed to provide commercially acceptable levels of disease suppression (5).

Environmental management offers more promise than chemical sprays alone. Light suppresses sporulation of P. belbahrii, with continuous light or supplemental lighting during nighttime hours substantially reducing spore production (6). Growers can exploit this by maintaining photoperiods longer than 13 hours or by using low-intensity supplemental lighting during dark periods. Reducing leaf wetness duration is equally important because the pathogen requires at least 24 hours of continuous moisture for infection and dense sporulation (7). In hydroponic systems, switching from overhead misting to sub-canopy irrigation and increasing air movement with horizontal airflow fans can dramatically reduce infection pressure (8).

Temperature manipulation provides another non-chemical tool. Passive heat treatment using transparent plastic covers to raise greenhouse temperatures during sunny periods suppressed downy mildew development without damaging basil plants (9). Temperatures above 30°C inhibit sporangiophore formation and sporangial germination, though plants must be acclimated gradually to avoid heat stress. This approach works best in greenhouse operations with sufficient ventilation control and may be less practical in open hydroponic facilities.

Varietal resistance remains the most effective long-term strategy for hydroponic basil growers. Breeding efforts have identified resistance sources in wild basil species Ocimum americanum, and these traits have been successfully transferred into sweet basil backgrounds (10). Commercial varieties with improved resistance are now available, though complete immunity has not been achieved. Growers should prioritize these resistant cultivars and combine them with environmental controls rather than relying on organic fungicide sprays.

Cropping system modifications can reduce disease pressure in organic systems. Research on open field organic production found that sparse sowing density combined with resistant varieties provided better control than chemical treatments alone (11). In hydroponics, maintaining wider plant spacing, particularly in NFT or DWC systems where humidity tends to be higher, allows better air circulation and faster leaf drying after irrigation events.

The reality for hydroponic basil producers is that organic foliar sprays, when used alone, will not provide adequate downy mildew control on susceptible varieties. The pathogen’s rapid lifecycle, preference for humid greenhouse conditions, and resistance to contact fungicides makes chemical intervention largely ineffective without supporting measures. Successful organic management requires integrating resistant varieties, environmental manipulation (particularly light, humidity, and leaf wetness control), appropriate plant spacing, and vigilant monitoring for early disease detection. Growers who continue relying primarily on organic sprays should expect continued losses, while those who adopt integrated approaches combining genetics and environment will achieve better results.




Calcium silicate (wollastonite) in soilless crops

Silicon in media is not a magic switch. In soilless systems it can help, it can do nothing, and at the wrong rate or pH it can hurt. Calcium silicate sources such as wollastonite release plant-available Si into inert substrates and typically raise pH, which is useful in peat but potentially more risky in coir or already alkaline systems. A recent substrate study quantified this clearly: wollastonite steadily released Si for months and increased media pH about 0.5 to 1 unit depending on substrate composition (1). With that in mind, here is the evidence for tomatoes and cucumbers grown without soil, focusing only on media or root-zone applications.

Vansil CS-1, one of the most common forms of calcium silicate (wollastonite) used as an amendment in soilless crops.

Tomatoes

Two independent Brazilian groups that amended substrate with calcium silicate found quality benefits but also rate-sensitivity. In a factorial test across Si sources and doses, calcium silicate treatments improved postharvest durability and maintained physicochemical quality of fruits; the effect size depended on the source and the dose used (2). A protected-environment pot study that mixed calcium silicate into the substrate before transplanting reported reductions in gas exchange and chlorophyll at midcycle at higher rates, a warning that more is not always better (3). Earlier yield work that compared sources also detected response to silicon fertilization in tomatoes, but the magnitude varied with rate and material (4).

Cucumbers

When wollastonite was incorporated into the soilless substrate, 3 g L⁻¹ increased yield by ~25% under moderate moisture restriction, with no penalty to soluble solids or fruit size. Lower doses or excessive irrigation did less (5). A separate work that applied a calcium-silicate solution into the substrate showed small gains in biomass under specific moisture regimes and no change in soluble solids, again pointing to context and dose as the deciding factors (6).


Practical takeaways for media use

  1. Treat calcium silicate like a weak liming Si source. Expect a pH rise. In peat this can be helpful, in coir or high-alkalinity waters it can push you out of range (1).
  2. Dose conservatively, then verify with tissue Si or leachate pH before scaling. Tomatoes show rate-sensitive physiology (3).
  3. Target crops and situations with the strongest evidence. Cucumbers under moderate moisture restriction and strawberries in organic substrates show the clearest yield and quality benefits (5), (7).

Summary table – media or root-zone Si only

Crop Medium and Si source Application rate Positive effects on yield or quality Reported negatives Ref
Tomato Substrate mix, calcium silicate among Si sources Field-equivalent 0 to 800 kg SiO₂ ha⁻¹ mixed pre-plant Improved postharvest durability and maintained physicochemical quality vs control; effect depended on dose and source None specified at optimal rates (2)
Tomato Substrate, calcium silicate mixed before transplant 0, 150, 300, 450, 600 kg ha⁻¹ Reduced gas exchange and chlorophyll at midcycle at higher rates, indicating potential performance penalty (3)
Tomato Substrate, silicon sources including calcium silicate Multiple rates Yield responded to Si fertilization depending on source and rate (4)
Cucumber Soilless substrate, wollastonite 3 g L⁻¹ of substrate under 75-85% container capacity +24.9% yield vs untreated; fruit size and soluble solids unchanged None noted at that rate (5)
Cucumber Substrate drench, calcium silicate solution 50-100 mg L⁻¹ SiO₂ applied to substrate Biomass gains under specific moisture regimes; quality unchanged No quality gain at tested doses; response moisture-dependent (6)
Any Peat or coir mixes, wollastonite ~1 g L⁻¹ media typical in study Steady Si release over months supports long crops Raises media pH by about 0.5-1 unit depending on substrate (1)

Bottom line

Use calcium silicate where the crop and context justify it, not by default. For cucumbers and strawberries the upside on yield and quality is most consistent when Si is in the root zone. For tomatoes, treat calcium silicate as a quality tool with a narrow window and verify plant response; higher rates can backfire physiologically. If you want to try calcium silicate, mix wollastonite with your media at a rate of 3g L⁻¹, then test the effect on pH and Si in tissue.




A low cost DIY oil IPM for your crops

An emulsified vegetable oil spray can smother mites and soft-bodied insects and can suppress powdery mildew if you actually coat the target. Soybean oil has the strongest evidence. Corn oil works too, and blending the two offers some advantages. In the following article I tell you how to prepare such a spray as well as some of the scientific evidence showing how it works.

Corn oil, one of the main components of this IPM spray

Why combine soybean and corn oil?

  • Fatty acid profiles differ. Soybean oil is richer in unsaturated fatty acids (linoleic, linolenic), while corn oil contains more oleic and palmitic. That mix can change the viscosity and spreading behavior on leaves.
  • Broader efficacy. Soybean oil has strong data against powdery mildew, mites, and whiteflies (1) (2) (3). Corn oil has been validated in cucumber mildew trials (5). Using both hedges against variability between pests and crops.
  • Physical properties. Mixed oils can emulsify more easily and form finer droplets than a single oil, which may improve coverage and reduce visible residues.

Why use both Tween 20 and Tween 80?

  • Hydrophilic balance. Tween 20 (polyoxyethylene sorbitan monolaurate) is more hydrophilic, while Tween 80 (polyoxyethylene sorbitan monooleate) is more lipophilic. Together, they stabilize emulsions of mixed triglyceride oils better than either one alone.
  • Reduced creaming/separation. A dual-Tween system forms smaller, more stable droplets that resist breaking apart. This means the concentrate stays uniform longer and the spray deposits more evenly on foliage (4).

Step 1. Prepare the concentrate

Mix in a clean container:

  • Soybean oil: 200 mL per liter (~760 mL per US gallon)
  • Corn oil: 200 mL per liter (~760 mL per US gallon)
  • Tween 20: 10 mL per liter (~38 mL per gallon)
  • Tween 80: 10 mL per liter (~38 mL per gallon)
  • Fill with clean water to reach 1 L (or 1 gal).

Mix for at least 30 minutes, ensure it is uniform. Always mix well before use. This is the concentrate: 20% soybean oil, 20% corn oil, 1% Tween 20, 1% Tween 80.

Step 2. Dilute for spraying

For foliar application:

  • Dilution rate: Add ~20mL of concentrate per liter of water (~75 mL per US gallon of water). If pests are present you can increase the rate up to 32mL/L (~120mL/gal).
  • Note on coverage: Coverage is critical for this spray to work as it only kills insects on contact or prevents PM by building an oil film on the leaf that prevents spore germination. Without full coverage effectiveness will drop.

This produces a 0.8% oil spray with 0.02% Tween 20 and 0.02% Tween 80 in the final spray solution. Mix well before use.

Shelf life considerations

  • Concentrate: A freshly prepared concentrate can stay stable for several weeks if kept sealed, cool, and out of light. Always shake well before use, since some slow separation can occur.
  • Diluted spray: Once mixed with water, use the spray the same day. Emulsions can separate within 12-24 hours, and microbial growth in water can destabilize the mix. Discard leftovers rather than storing diluted spray.
  • Indicators of instability: Layering, large oil droplets, or visible separation mean the emulsion is breaking, don’t spray that on plants without mixing well again.

Why it works

Soybean oil sprays at 2% suppressed powdery mildew on roses and tomatoes (1), reduced spider mites by 97-99% (2), and deterred whiteflies (3). Corn oil added control of cucumber mildews (5). Tweens stabilize and spread the oils (4).

Bottom line

  • Concentrate: 200 mL soybean oil + 200 mL corn oil + 10 mL Tween 20 + 10 mL Tween 80 per liter (or 760 mL + 760 mL + 38 mL + 38 mL per gallon), topped up with water.
  • Spray dilution: 75 mL concentrate per gallon of water.
  • Final spray: 0.8% oil, 0.02% Tween 20, 0.02% Tween 80.
  • Shelf life: Weeks for concentrate (if stored sealed, cool, dark); hours for diluted spray.

This blended, dual-Tween foliar spray is a low-cost, evidence-backed way to add an oil-based control into hydroponic IPM programs.




Recent advances in hydroponic cucumber cultivation: media, irrigation, nutrition and biostimulants

Cucumber has become a model crop for testing new soilless technologies, with greenhouses adopting alternative substrates, precision fertigation and biostimulants. Over the last decade a series of peer-reviewed studies have clarified what actually shifts growth and yield, and what is still more hype than practice.

A soilless cucumber greenhouse using coco coir.

Substrate choices: coir, waste materials and microbiome effects

The clearest advance is the repeated demonstration that coconut coir outperforms rockwool in cucumbers. A 2022 Heliyon study reported higher leaf area index, greater yields and increased mineral content (Ca, Mg, S, Cl, Zn) in coir compared with rockwool, alongside shifts in fruit amino acids and flavor compounds (1). This is not marginal, it reflects both physiology and quality.

Efforts to cut peat use are also accelerating. A 2025 Scientific Reports trial tested agricultural wastes such as cocopeat, palm peat, vermicompost, sawdust and pumice, finding several blends that produced transplant vigor comparable to peat moss (2). Another study replaced cocopeat with rice straw, sawdust and compost over two seasons; rice straw and coir-rice blends gave the best irrigation water productivity and photosynthesis with yields close to cocopeat (3). In parallel, wood fiber has been tested in combination with peat under staged nitrogen inputs, showing that fiber proportion and N rate jointly determine nutrient uptake efficiency (4).

Beyond performance metrics, substrate strongly shapes the cucumber root microbiome. A 2022 Frontiers in Microbiology study showed that different artificial substrates led to distinct bacterial community structures and predicted functions in roots, highlighting that choice of media can influence not only plant nutrition but also microbial dynamics (6).

Finally, biochar-compost amendments are emerging as candidate peat replacements. A 2023 trial demonstrated improved cucumber seedling growth with certain biochar-compost mixes, though physical properties still dictated success (5).

Takeaway: Coir is a proven upgrade over rockwool. Waste-based and fiber blends can substitute part of peat if their hydrophysical traits are tuned. Substrates also rewire root microbiomes, adding another layer to consider.


Irrigation and fertigation: oxygenation and nutrient recipes

Irrigation research has focused on dissolved oxygen. A 2023 Scientific Reports paper tested micro-nano bubble irrigation: raising water DO from ~4 to 9 mg·L⁻¹ increased yield and irrigation water use efficiency by ~22%, while boosting vitamin C, soluble solids and photosynthesis (7). The effect is practical, low oxygen is common in dense cucumber crops under low light.

On the nutrient side, hydroponics consistently outperforms soil. A 2025 Scientific Reports comparison found cucumbers in Hoagland solution under soilless culture had taller plants, more flowers and nodes, and 9-19% more fruits than soil-grown controls on alternative formulations (8). These are large differences that underscore the importance of using a complete, balanced solution and not cutting corners on formulation.

Takeaway: Boosting dissolved oxygen is a low-cost irrigation improvement. And nutrient recipes matter, generic soil formulas do not translate well to hydroponics, where Hoagland-type solutions remain robust.


Nutrient interactions: silicon and iron

Element interactions are less visible but no less important. A 2020 Frontiers in Plant Science study showed that supplying silicon in hydroponics triggered iron deficiency responses in cucumber, even under adequate Fe, and altered recovery after resupply (9). This is a reminder that “beneficial” elements are not always benign and should be managed carefully, especially when layering biostimulants or micronutrient supplements.


Biostimulants and stress management

Humic substances remain the most tested tools. A 2024 Scientific Reports study under 10 dS·m⁻¹ NaCl found that foliar humic acid sprays, especially when combined with grafting onto tolerant rootstocks, improved cucumber growth, antioxidant activity and secondary metabolism relative to untreated controls (10). This reinforces humics as a stress-mitigation option rather than a universal growth booster.

Microalgae are also being trialed. A 2023 MDPI study using Chlorella vulgaris suspensions increased root dry biomass of cucumber seedlings in hydroponic culture (11). The shoot response was more variable, but the root effect suggests promise for early growth stages.

Grafting remains a practical biostimulant in the broad sense. A 2023 Environmental Pollution study showed that salt-tolerant rootstocks reduced Na transport into cucumber shoots, improving yield and fruit quality under salinity (12).

Takeaway: Humic acids and grafting can buffer salinity stress, while microalgae show root growth potential. None of these replace proper fertigation, but they add resilience once fundamentals are stable.


Practical synthesis

  1. Switch to coir if you are still on rockwool. Yield and mineral improvements are consistent (1).
  2. Trial waste substrates cautiously. Rice straw and fiber blends can work, but only when physical properties are controlled (2) (3).
  3. Oxygenate irrigation water. in NFT systems Aiming for ~9 mg·L⁻¹ DO has measurable payoffs in yield and quality (7).
  4. Use complete nutrient recipes. Hoagland still outperforms incomplete alternatives (8).
  5. Watch element interactions. Silicon can complicate iron nutrition in hydroponics (9).
  6. Layer biostimulants for stress, not yield. Humic acids, grafting and microalgae add tolerance or early root vigor but only after fertigation and media are optimized (10) (11) (12).



Moringa extract as a biostimulant in hydroponics

Moringa leaf extract (MLE) is a rather recent addition to the biostimulant market. Below I focus on peer-reviewed work in hydroponic or soilless systems, with attention to yield, quality, toxicity, and dose timing.

Moringa plant leaves, commonly used to create extracts

Evidence and discussion

Hydroponic lettuce. A greenhouse hydroponic study applied MLE at transplant via root dip, then three foliar sprays at 10-day intervals. Marketable yield increased around 30% vs control, leaf area rose, and leaves were less susceptible to Botrytis after harvest. The paper characterized MLE chemistry but treated it mainly as a formulated extract; the schedule, not just the material, clearly mattered (1).

Tomato in soilless culture. In cherry tomato, four applications of 3.3% w/v MLE, given every two weeks as either foliar or root drenches, improved biomass and increased fruit yield and quality metrics like soluble sugars, protein, antioxidants, and lycopene. 3.3% equals ~33 000 ppm. The same trial compared MLE to cytokinin standards and found MLE competitive when applied on a schedule, not just once (2).

Pepper and tomato under protected cultivation. A peer-reviewed study in a protected environment tested weekly foliar sprays from two weeks after transplant until fruit set. Tomato and pepper showed higher chlorophyll index and fruit firmness, with cultivar-dependent yield gains (3). A separate field-protected trial in green chili parsed delivery method and concentration: seed priming plus foliar MLE at 1:30 v/v (3.3%) delivered the most consistent improvements in growth and a ~46% rise in fruit weight per plant; vitamin C in fruit climbed up to ~50% with foliar 1:20 v/v (5%) (4).

Quality and nitrate in leafy greens. Lettuce grown under glasshouse conditions responded to 6% MLE foliar sprays with higher vitamin C and polyphenols in one season, and lower nitrate accumulation in another. Six percent equals ~60 000 ppm. Effects were season and cultivar dependent, which should temper expectations (5).

Reviews for context. Two recent reviews summarize MLE’s biostimulant activity and mechanisms, with repeated emphasis on dose and frequency dependence and the reality that extraction protocol changes outcomes. They also highlight hormesis and allelopathic risks at higher doses or with sensitive species (6), (7).

Responses are real but system-specific. Yield and quality gains show up most consistently when MLE is scheduled repeatedly at moderate concentrations and aligned with crop phenology.

Reported effects on yield and quality in hydroponic/soilless crops

Crop & system MLE dose (%) Application method & timing Yield effect Quality effect Source
Lettuce, perlite hydroponic Not explicitly stated; applied as standardized aqueous extract Root dip at transplant, then foliar sprays every 10 days ×3 Marketable yield ↑ ~30% vs control Higher pigments and total phenolics; postharvest Botrytis severity ↓ 32% (1)
Cherry tomato, soilless pots 3.3% 100 mL per plant, foliar or root, every 14 days ×4 Fruit yield ↑ 26–38% depending on route Fruit sugars, protein, antioxidants, lycopene ↑ (2)
Tomato, protected soilless Not reported Weekly foliar from 2 WAT to fruit set Positive, cultivar dependent Higher chlorophyll index; firmer fruit (3)
Green chili pepper, protected 3.3%, 5%, 10% Seed priming ± foliar; best was priming + 1:30 foliar Fruit weight per plant ↑ ~46% with priming+1:30 Vitamin C ↑ up to ~50% with 1:20 foliar; no change in capsaicin (4)
Lettuce, glasshouse substrate 6% Foliar, seasonal trials Season dependent Vitamin C and polyphenols ↑ in 2020; nitrate content ↓ in 2019 (5)

Practical dosing windows

Crop When to apply Practical note Source
Lettuce (hydroponic) Transplant dip, then every 10 days through vegetative phase Schedule matters at least as much as concentration in this protocol (1)
Tomato Every 14 days from early vegetative through early fruiting, foliar or root 3.3% worked across routes; root drenches often gave stronger biomass responses (2)
Pepper Seed priming before sowing plus early foliar during preflower to fruit set Combined priming and 3.3% foliar outperformed single methods (4)
Tomato and pepper Weekly foliar from 2 WAT to fruit set Useful pattern for protected cultivation programs (3)

Toxicity and limits

Reviews document allelopathic and inhibitory effects at higher doses, with hormesis explaining the switch from stimulation to suppression as concentration increases. Sensitive species and young tissues are at greater risk. Use consistently timed foliar applications for best results, these have been studied much more thoroughly across many more crop species. MLE has inhibitory effects on seed germination and seedling growth for some plants, so refrain from using in very early crop stages unless the species isn’t sensitive (6), (7).

Conclusions

If you want to test MLE in hydroponic or soilless production, use the following guidelines:

  1. Use moderate concentrations in the 3-5% range for foliar applications (safer than root applications).
  2. Time applications with vegetative growth and preflower phases, repeating at weekly intervals.
  3. Expect cultivar and season effects, especially regarding quality.
  4. Lookout for toxicity symptoms if using higher concentrations (>5%).
  5. Test carefully before using on seedlings or recently rooted cuttings.

Do the basics right and you can get measurable gains in yield and quality with less risk of phytotoxicity. The citations above should help guide your use of this new biostimulant.




Exogenous Root Applications of Wetting Agents in Soilless Media

Introduction

Dry peat, coir, rockwool or bark mixes can become water repellent, which creates uneven moisture and nutrient delivery around roots. Wetting agents reduce surface tension and restore wettability by improving water contact with hydrophobic surfaces, an effect well documented for organic growing media used in horticulture (6). In soilless systems, exogenous root applications are used to correct dry-back, stabilize irrigation performance, and improve nutrient distribution. This post reviews what has been tested, how these agents affect mineral nutrition, water uptake, yield and quality, known toxicity limits, and realistic application rates.

Effect of surfactants on roots. Taken from (7)

Evidence and discussion

Types tested

Most root-zone wetting agents in horticulture are nonionic surfactants such as alcohol ethoxylates, block copolymers, or organosilicone derivatives; anionic formulations are less common for routine root use due to higher phytotoxic risk, while cationic types are generally avoided; amphoteric agents are used less frequently but appear in some products. The role of wetting agents to counter water repellency in organic media is supported by a comprehensive review of wettability mechanisms and amendments (6).

Water uptake and distribution

In rockwool and coir, adding a nonionic surfactant to the fertigation stream at doses from 2 to 20 000 ppm showed that a minimal dose could be sufficient: 2 ppm increased easily available water by more than 600 percent, while higher concentrations gave no extra benefit (1). Across peat, coir, and bark, wetting agents improved hydration efficiency, although severely dry materials retained some hydrophobic pockets that were not fully overcome by surfactant treatment (2).

Mineral nutrition

In a melon crop on rockwool and reused coco fiber, weekly fertigations with a nonylphenol ethoxylate at about 1000 ppm reduced nitrate and potassium losses in drainage and increased potassium uptake, while leaving total water use and pH unchanged (3). In lettuce, fertigation with a nonionic organosilicone-type surfactant at 200 ppm and 1000 ppm improved nutrient use efficiency without increasing yield, indicating better capture of applied nutrients for the same biomass and specifically in field trials with a methyl-oxirane nonionic surfactant. Direct lettuce evidence of improved nutrient use efficiency and root-zone wetting with ~200–1000 ppm doses comes from an in-field trial using a nonionic methyl-oxirane surfactant (6) and is detailed further under quality effects below.

Yield and quality

Yield responses depend on whether water distribution was limiting. In lettuce, the nonionic surfactant improved nutrient use efficiency but did not increase marketable yield under well-watered conditions. Quality can benefit: lettuce fertigated with a nonionic methyl-oxirane surfactant at ~1000 ppm showed a significant reduction in leaf nitrate accumulation compared with controls, alongside indications of shallower, more uniform wetting of the upper root zone (6).

Persistence and accumulation

Repeated use matters. In sand models, a polyoxyalkylene polymer surfactant (PoAP) sorbed to particles and increased hydrophobicity after repeated applications, whereas an alkyl block polymer (ABP) maintained or improved wettability and did not leave a hydrophobic residue. Chemistry dictates long-term behavior, so product choice is critical (4).

Toxicity

There is a hard ceiling for some agents. Hydroponic lettuce exposed to the anionic detergent Igepon showed acute root damage at ≥250 ppm, with browning within hours and growth suppression, although plants recovered after the surfactant degraded in solution (5). Practical takeaway: avoid harsh anionic detergents and keep any surfactant well below known toxicity thresholds.

Tables

Table 1. Water behavior in soilless substrates after root-zone wetting agents

Study (Ref) System and media Surfactant and dose Key outcome
(1) Rockwool and coir, new and reused Nonionic surfactant, 2–20 000 ppm 2 ppm raised easily available water by >600 percent; higher doses gave no additional gain
(2) Peat, bark, coir under different initial moistures Commercial wetting agent, low to high Hydration efficiency improved across materials, but extremely dry media retained some hydrophobic zones

Table 2. Nutrient dynamics, yield, quality, and safety

Study (Ref) Crop and system Regime and dose Observed effect
(3) Melon in rockwool and reused coco Weekly fertigation at ~1000 ppm Lower nitrate and potassium leaching, higher K uptake, no change in water use or pH
(6) Lettuce, fertigated field context Nonionic surfactant ~200–1000 ppm Improved nutrient use efficiency; neutral yield response; reduced leaf nitrate at higher dose
(4) Sand columns, repeated applications PoAP vs ABP, repeated dosing PoAP accumulated and increased hydrophobicity; ABP maintained or improved wettability
(5) Lettuce in hydroponics Anionic detergent ≥250 ppm Acute root phytotoxicity at and above 250 ppm; recovery after degradation of the agent

Practical rates

In closed hydroponic or recirculating fertigation, start conservatively. Research showing benefits without injury typically used ~50–1000 ppm, with several studies centering on ~1000 ppm weekly pulses in drip systems, or ~200–1000 ppm continuous-equivalent dosing in trials on leafy greens (3) (6). Very low concentrations can already fix wettability issues, as the 2 ppm result illustrates (1). Always monitor for foaming, root browning, or oily films. Avoid cationic disinfectant-type surfactants at the root zone and keep anionic detergents far below the 250 ppm lettuce toxicity threshold (5). Choose chemistries that do not accumulate with repeated use (4).

Conclusion

For soilless production, exogenous root applications of wetting agents are a precise way to restore uniform wetting, stabilize nutrient delivery, and improve nutrient use efficiency. Expect neutral yield when irrigation is already optimal, but better quality in leafy greens via lower leaf nitrate, and less nutrient loss in drain when media are reused or prone to channeling. Use the lowest effective ppm, prefer nonionic chemistries validated in horticultural systems, and be wary of products that persist or sorb to media. Done right, wetting agents are a small, high-leverage tweak that keeps the entire root zone working for you, not against you.




Recent findings in hydroponic and soilless strawberries: a data-first look at the last decade

Strawberry in controlled environments is not short on opinions. Research from the past 10 years has given us a lot of information on strategies to increase yields and reduce costs. Below I synthesize recent findings, aiming to provide you with practical information that can help you improve your crop. I focus first on mineral nutrition, then biostimulants, exogenous hormone applications, and pruning or cultural practices. When concentration units were not reported in ppm, I converted them. Where authors only gave mL L⁻¹ of a commercial product, I report ppm v/v and, when possible, ppm of active ingredients.

A picture of a soilless strawberry crop

What the evidence says

Mineral nutrition that consistently improves output

  1. Stage-specific K:N balance matters more than one static recipe. A greenhouse pot trial in soilless bags across three cultivars found that running a higher K:N balance in vegetative growth, then lowering it in production, delivered the best overall performance. Their S2 program (growth K:N 2.6, production K:N 1.0) raised yield by 30 percent and improved firmness and shelf-life metrics compared to other balances, with equal seasonal totals of N, P, K, Ca, Mg across treatments. This is one of the clearest, practical levers reported for soilless production in the last decade (1).
  2. Absolute NO3⁻ and K setpoints still matter, but the optimum is not “more is better”. A hydroponic study that orthogonally varied nitrate and potassium in soilless strawberries showed that 15 mM NO3⁻ increased yield while higher K favored nutraceutical quality. Converting their molarities to ppm: 9, 12, 15 mM NO3⁻ equal 126, 168, 210 ppm N as nitrate and 558, 744, 930 ppm NO3⁻, while 5, 7, 9, 11 mM K⁺ equal 196, 274, 352, 430 ppm K. The highest yields occurred at the upper end of their NO3⁻ range, with quality improving as K approached 430 ppm K. Takeaway: push N during heavy fruiting if you can keep flavor in check, and use K to tune quality targets (2).
  3. Simply cranking K in water-culture will backfire. A 2025 deep-water culture trial that stepped K from 117 to 348 ppm at constant 77 ppm N found no yield benefit and, in some cases, reduced fruit size and total yield as K rose. Translation: chasing high EC by piling on K is noise, not signal, in DWC strawberries (3).
  4. The nitrate fraction can be used as a steering tool without changing total N. A 2025 soilless study that varied the percentage of total N supplied as nitrate from 0 to 100 percent across three cultivars showed meaningful shifts in plant N status and leachate pH, offering a route to manage uptake and alkalinity without changing ppm N. This is more about stability and diagnosis than raw yield, but it is actionable in recirculating systems (4).
  5. System choice is not neutral. A 129-day greenhouse comparison found a coir-based substrate system substantially outperformed three water-culture systems (NFT, vertical stacked flow, aeroponics) for total yield and resource-use efficiency in ‘Florida Brilliance’ and ‘Florida Beauty’. If your priority is marketable kilograms per square meter, substrate is still the safe bet unless you have a very strong reason to go water-culture (5).

Biostimulants with greenhouse soilless data

Two solid greenhouse papers in soilless bags make this practical:

• A nutrient-limitation stress trial in soilless ‘Elsanta’ tested 10 foliar biostimulants. Several treatments improved marketable yield and fruit quality under low fertility. Doses were applied as labeled mL L⁻¹; I report them as ppm v/v. Effects were strongest for specific protein hydrolysates and seaweed extracts, with chitosan showing quality gains rather than yield spikes (6).

• A head-to-head in substrate culture directly compared commercial plant biostimulants and synthetic auxins. The best biostimulant program matched or exceeded auxin-based fruit set under the tested conditions, and the paper fully discloses active contents for the auxin products, which lets us convert to ppm actives for fair comparison (7).

Exogenous hormone applications

Soilless strawberry papers using PGRs are fewer than field studies, but the 2024 greenhouse comparison above provides what growers need: dose-disclosed auxin programs in substrate bags, with yield and quality outcomes. The synthetic auxin formulation Auxyger was listed at 6.7 g L⁻¹ NAA + 16.9 g L⁻¹ NAD. At 0.5 mL L⁻¹, that is 3.35 ppm NAA and 8.45 ppm NAD actives. In that trial, the best protein hydrolysate program rivaled or beat this auxin program on yield while improving certain quality attributes, which makes a case for biostimulant-first strategies where regulations or buyer specs frown on PGR residue (7).

Pruning and culture practices with measurable, repeatable gains

• Runner control increases yield in everbearing cultivars under tabletop tunnel production. Bi-weekly runner removal in ‘Favori’ increased total and marketable yield per plant and improved average berry size, while partial defoliation reduced both. This is not a subtle effect; it is sink management and it pays off (8).

• Planting density in greenhouse substrate is a yield vs. cull tradeoff, not a free lunch. A two-season soilless trial in troughs found 5 to 15 cm in-row spacing maximized commercial fruit and profitability for ‘Pircinque’, but the densest spacings increased small and discarded fruit percentage. If labor for canopy management is tight, 10 to 15 cm is the saner operating point (9).

• System selection again: when in doubt, choose substrate if your KPI is kilograms. The 2025 greenhouse head-to-head is clear that coir-based substrate outperformed water-culture for both yield and resource efficiency in their conditions (5).

Mineral nutrition highlights in soilless strawberries

Study & system Factor Setpoints converted to ppm Observed effect
Preciado-Rangel 2020, soilless culture (2) NO3⁻ and K in solution NO3⁻ at 126, 168, 210 ppm N (558, 744, 930 ppm NO3⁻). K at 196, 274, 352, 430 ppm K Higher NO3⁻ increased yield, higher K improved nutraceutical quality; best yields at 210 ppm N with K toward 430 ppm K.
Ries 2025, deep-water culture (3) K at constant 77 ppm N 117, 194, 271, 348 ppm K Increasing K above 117 ppm did not improve yield or fruit size; higher K often reduced fruit size and yield.
Yafuso 2025, soilless substrate (4) Percent of total N as nitrate 0 to 100 percent of total N as NO3⁻ at a fixed total N (ppm not changed) Adjusting nitrate fraction shifted foliar N and leachate pH, offering control without changing ppm N.
Nakro 2023, greenhouse soilless (1) K:N balance over time Growth phase K:N 2.6, production phase K:N 1.0 (ratios) Program raised yield 30 percent and improved firmness and shelf-life vs other balances.

Biostimulants in soilless strawberries

Product or molecule Type Dose used in study (ppm) Cultivar & system Observed effect Source Notes
Protein hydrolysate (Trainer) Amino acid hydrolysate 5000 ppm v/v (5 mL L⁻¹) ‘Elsanta’ in peat-based substrate Increased marketable yield and improved quality under nutrient limitation (6) Labeled concentration is mass per kg; ppm v/v reported for transparency.
Seaweed extract Ascophyllum-based 2500 ppm v/v (2.5 mL L⁻¹) ‘Elsanta’ in substrate Yield and antioxidant gains under low fertility (6) Product-label dose.
Chitosan solution Biopolymer 10000 ppm v/v (10 mL L⁻¹) ‘Elsanta’ in substrate Quality improvements more than yield (6) DDA: NR, molar mass: NR in paper.
Protein hydrolysate program Amino acid hydrolysate 5000 ppm v/v (5 mL L⁻¹) Greenhouse substrate bags Matched or exceeded auxin program on yield while improving specific quality traits (7) See auxin row for direct comparison.

Exogenous hormones tested in soilless conditions

Active(s) Class Dose as actives (ppm) Product dose Cultivar & system Observed effect Source
NAA + NAD Synthetic auxin + cofactor 3.35 ppm NAA + 8.45 ppm NAD calculated from 6.7 g L⁻¹ NAA + 16.9 g L⁻¹ NAD at 0.5 mL L⁻¹ 0.5 mL L⁻¹ Greenhouse substrate bags Increased fruit set and yield vs water control, but best protein hydrolysate program was competitive on yield with added quality benefits (7)

Pruning and cultural practices in soilless systems

Practice Setting Quantified outcome Source
Bi-weekly runner removal Everbearing ‘Favori’ in tabletop tunnel Higher total and marketable yield and larger berries vs keeping runners; defoliation reduced yield (8)
In-row spacing 5 to 15 cm Greenhouse troughs, soilless substrate Highest commercial yield and profitability with 5 to 15 cm, but denser plantings increased culls; 10 to 15 cm safer if labor is limited (9)
System choice: substrate vs water-culture Greenhouse, coir substrate vs NFT, vertical, aeroponics Substrate system delivered the highest yield and best resource-use efficiency in both tested cultivars (5)

Practical summary

• If you run substrate culture, start with a sane base recipe and adopt a two-phase K:N strategy. Push K:N in vegetative growth to build canopy and sink capacity, then lower K:N in production to support sustained fruiting. The 2.6 then 1.0 K:N program is the best documented template right now and lifted yield by 30 percent in greenhouse soilless conditions (1).

• For absolute targets during heavy fruiting, do not be shy about 200 ppm N as nitrate if fruit flavor is maintained, and keep K in the 350 to 430 ppm range to pull quality without sacrificing mass. That is where the 2020 hydroponic NK grid saw the best balance (2).

• Water-culture is unforgiving with K. Above roughly 120 to 200 ppm K in DWC at moderate N, returns were negative in 2025 work, so treat “more K” as a risk factor rather than a lever in water-culture strawberries (3).

• Biostimulants can be yield-positive under stress and can stand toe-to-toe with low-dose auxin programs in substrate. If you need a conservative starting point, weekly foliar protein hydrolysate at 5000 ppm v/v is the most replicated choice across the soilless greenhouse literature summarized here (6), (7).

• Exogenous auxins at single-digit ppm actives work, but they are not automatically superior to a strong biostimulant program in greenhouses. If you use auxins, be precise about actives. The 0.5 mL L⁻¹ Auxyger rate equals 3.35 ppm NAA + 8.45 ppm NAD. Compare like with like, not mL of product (7).

• Cultural practices still pay the bills. Remove runners on a schedule in everbearers and do not defoliate unless you enjoy losing yield (8). Pick a density you can actually manage. If labor is tight, 10 to 15 cm spacing is a rational compromise in tabletop or trough systems (9). If you are choosing systems with yield as the top KPI, substrate culture remains the safest option in 2025 greenhouse data (5).




Recent advances in the cultivation of CEA tomatoes: evidence from 2015–2025

Hydroponic tomato yields are already high, yet many operations still leak performance through nutrient scheduling, canopy design, and stress control. Below is a blunt, data-driven synthesis for controlled environments based on recent scientific studies. The pattern is consistent: stabilize nutrition and irrigation first, then layer biostimulants or hormones only where trials show a payoff.

A soilless cherry tomato crop. Photo courtesy of Pakistan Hydroponics. You can watch their farm here.

Mineral nutrition and solution management

A 2024 greenhouse study across six cultivars found that a constant nutrient concentration program matched yield and improved size distribution compared with stage-based ramps when EC was well controlled (1). A 2023 review distills current best practice for recirculating systems, stressing stage-appropriate EC, ion ratios that avoid antagonisms, and disciplined monitoring in closed loops (2).

Closed systems are viable when sanitation and monitoring are tight. A greenhouse comparison showed closed hydroponics achieving similar yields with better water and fertilizer use efficiency than open run-to-waste setups (3). Calcium balance still matters. Whole-plant experiments showed that simply pushing calcium does not prevent blossom-end rot and that imbalances can backfire, so keep Ca adequate and balanced rather than excessive (4).

Irrigation and pruning practices that scale

Partial root-zone drying and moderate deficit irrigation remain the most defensible water-saving tactics in greenhouses. Grafted tomatoes under PRD or deficit regimes saved 30 to 40 percent water with only minor yield penalties and sometimes higher fruit mineral concentrations (5).

On canopy design, a low-truss high-density approach can raise kilograms per square meter. In a hydroponic sub-irrigated trial with the indeterminate hybrid Rebeca, the top treatment was two trusses per plant at 11.1 plants per square meter, reaching 22.61 kg per square meter in 134 days without harming fruit quality (6).

Biostimulants with signal, not hype

Seaweed extracts and chitosan have the most consistent tomato evidence in soilless systems.

A greenhouse study in inert substrates showed that foliar seaweed extract at 100 000 to 200 000 ppm improved chlorophyll, gas exchange, and fruit quality indices. Silicon at 75 ppm (as sodium silicate) increased firmness and yield per plant in a palm-peat mix. Effects were substrate and dose dependent, so you must calibrate to your product and spray volume per area (7). A 2022 review synthesizes similar benefits for seaweed extracts under salinity stress, with gains tied to photosynthesis and ion homeostasis rather than magic bullets (8).

For chitosan, a 2025 greenhouse study on Floradade and Candela F1 tested 500, 1000, and 2000 ppm foliar programs. Higher rates improved growth and physiology, with cultivar-specific responses. Product specs like degree of deacetylation and molar mass were not reported, so do not assume equivalence across suppliers (9).

Exogenous hormones: targeted, not blanket

If fruit set is the bottleneck during heat or low pollen viability, exogenous hormones can help. In protected cultivation of cv. Srijana, a conservative foliar program of GA3 at 50 ppm with NAA at 25 ppm increased fruit set and total yield. The response surface penalized higher rates, reminding you that timing and dose are critical (10). For mechanism and limits, a 2022 review explains how auxin and gibberellin signaling induce parthenocarpy in tomato and why misuse leads to malformed fruit (11).

Summary tables

Table 1. Mineral nutrition and system practices with yield impact in CEA tomatoes

Factor Cultivar or type Dose or setting (ppm) Observed effect Source
Constant vs stage-based nutrient supply Six cultivars, greenhouse Program choice rather than dose Constant feed matched yield and improved size distribution (1)
Nutrient solution management review General CEA Program design Best practice for EC, ion ratios, and closed-loop monitoring (2)
Closed vs open hydroponics Determinate tomato, greenhouse System choice Closed loop improved water and fertilizer efficiency with comparable yield (3)
Calcium balance Modern genotypes Balanced Ca supply Lower BER risk depends on overall ion balance, not brute Ca (4)
Partial root-zone drying and deficit irrigation Grafted tomato, greenhouse Irrigation scheduling 30 to 40 percent water savings with minor yield penalties (5)

Table 2. Biostimulants in soilless tomatoes

Biostimulant Cultivar or type Application Dose (ppm) Observed effect Source
Seaweed extract Cherry tomato, greenhouse substrates Foliar 100 000 to 200 000 Improved physiology and fruit quality indices under stress (7)
Silicon as sodium silicate Cherry tomato, greenhouse substrates Foliar 75 Increased firmness and yield per plant in palm-peat mix (7)
Chitosan (medium MW, commercial) Floradade and Candela F1 Foliar, multiple sprays 500, 1000, 2000 Improved growth and physiological performance, cultivar dependent (9)
Seaweed extract review Multiple tomato types Seed or foliar in soilless culture Various Stress tolerance and modest yield gains under salinity (8)

Table 3. Exogenous hormone programs with documented yield or set effects

PGR Cultivar or type Application Dose (ppm) Observed effect Source
GA3 + NAA Srijana, protected cultivation Foliar during flowering GA3 50, NAA 25 Increased fruit set and total yield; higher rates underperformed (10)
Auxin and GA context Tomato, general Mechanistic review N/A Explains parthenocarpy induction and risks of misuse (11)

Practical takeaways

Do not chase clever ramps before you can hold EC steady. A constant, well-tuned feed can match yield and improve size distribution when the rest of the system is under control (1), (2). Closed loops pay only if you earn them with monitoring and sanitation (3). Low-truss high-density recipes push kg per square meter, provided irrigation and nutrition meet the faster sink demand (6). Seaweed extracts and silicon can help under stress, but responses are product and substrate specific. Chitosan works, yet cultivar and formulation matter, so trial first (7), (8), (9). Hormones are scalpels for set problems, not a replacement for climate and pollination management (10), (11).