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.

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:

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.

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).

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.

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.

Triacontanol is a naturally occurring long-chain fatty alcohol found in plant cuticle waxes that can act as a growth regulator at very low concentrations. Below I focus on peer-reviewed evidence for triacontanol in hydroponic and soilless systems, with attention to preparation methods, yield effects, and quality outcomes in tomatoes, cucumbers, strawberries, and lettuce.

Evidence for Yield and Quality Effects

Hydroponic lettuce. Foliar application of triacontanol at 10^-7 M (approximately 0.043 mg/L) to 4-day-old hydroponically grown lettuce seedlings increased leaf fresh weight by 13-20% and root fresh weight by 13-24% within 6 days. (1) When applied at both 4 and 8 days after seeding, leaf area and mean relative growth rate increased by 12-37%. There was no additional benefit from repeating applications beyond two sprays in this short-cycle crop.

Tomato in hydroponic systems. Weekly foliar applications of 70 µM triacontanol (approximately 21 mg/L) on tomatoes grown in hydroponic drip systems significantly increased flower number by 37-50% and total fruit number by 22-57%, resulting in a 28% higher total yield at harvest. (2) Individual fruit weight decreased by 16%, but the net effect on total productivity remained positive. The treatment advanced blooming without affecting plant height or internode number, demonstrating a specific effect on reproductive development.

Cucumber under soilless conditions. Foliar application of triacontanol at 0.8 mg/L on cucumber genotypes under salt stress improved photosynthesis, stomatal conductance, and water use efficiency. (3) The treatment enhanced antioxidant enzyme activities and maintained better membrane stability. Yield traits, including fruit number and average fruit weight, improved in response to triacontanol application. Salt-tolerant genotypes (Green long and Marketmore) showed greater responsiveness than sensitive genotypes.

Strawberry. Triacontanol has shown promise in improving drought tolerance in strawberry plants by enhancing growth, productivity, and physiological performance, though most work has been conducted in soil rather than true soilless systems. (4)

Formulation: Creating a Concentrated Stock Solution

Triacontanol has extremely low water solubility (less than 1 mg/L at room temperature), which makes proper formulation critical. The most reliable approach combines an organic solvent with a surfactant to create a stable concentrate that can be diluted into spray solutions.

Stock Solution Protocol

Materials needed:

• Triacontanol powder (90%+ purity)
• Ethanol (95% or higher)
• Tween-20 or Tween-80 (polysorbate surfactant)
• Distilled or deionized water
• Glass or high-density polyethylene containers

Preparation of 1000 mg/L (1000 ppm) stock:

1. Weigh 1000 mg of triacontanol powder using an analytical balance.
2. Dissolve the triacontanol in 100 mL of 95% ethanol in a glass beaker. Warm gently (35-40°C) while stirring with a magnetic stirrer for 15-20 minutes to ensure complete dissolution. Do not exceed 50°C.
3. Add 5 mL of Tween-20 to the ethanol solution and mix thoroughly for 5 minutes. This surfactant concentration (0.5% v/v in final volume) ensures proper emulsification and leaf surface wetting.
4. Transfer the ethanol-triacontanol-surfactant mixture to a 1000 mL volumetric flask.
5. Bring to final volume with distilled water while mixing continuously. The solution will appear slightly cloudy due to micelle formation, which is expected and desirable.
6. Store the stock solution in an amber glass bottle at room temperature. The stock is stable for 3-4 months when protected from light and heat.

Alternative solvent systems: Some studies have successfully used isopropanol or acetone as solvents. (5) However, ethanol provides the best combination of triacontanol solubility, plant safety, and ease of handling for growers.

Working Solution Preparation

Dilute the 1000 mg/L stock to achieve target concentrations based on crop and growth stage:

Lettuce: Dilute 1:10,000 to 1:20,000 for final concentrations of 0.05-0.1 mg/L. For a 1-liter spray bottle, add 0.05-0.1 mL of stock solution.

Tomato: Dilute 1:50 for final concentration of 20 mg/L. For a 1-liter spray bottle, add 20 mL of stock solution.

Cucumber: Dilute 1:1250 for final concentration of 0.8 mg/L. For a 1-liter spray bottle, add 0.8 mL of stock solution.

Add an additional 0.1% v/v Tween-20 (1 mL per liter) to the final spray solution to ensure maximum leaf coverage and absorption. This additional surfactant enhances uptake without phytotoxicity when concentrations remain below 0.2%. (3)

Application Timing and Frequency

Seedling stage: Apply once at 4-8 days after emergence for leafy greens in short-cycle production. A single early application is often sufficient for lettuce. (1)

Vegetative and reproductive stages: For fruiting crops like tomato and cucumber, apply weekly starting 4 weeks after transplant and continuing through flowering and early fruit set. Three to five applications total are typically used. (2) (3)

Application method: Apply using a hand sprayer or backpack sprayer with a cone nozzle, ensuring complete leaf coverage including undersides. Apply in early morning or late afternoon to maximize absorption and minimize evaporation. Spray until runoff just begins.

Reported Effects Across Crops

Mechanisms and Considerations

Triacontanol acts through a secondary messenger system involving 9-L(+)-adenosine, which triggers rapid ion influx (Ca²⁺, K⁺, Mg²⁺) and modulates gene expression related to photosynthesis, hormone balance, and stress responses. (2) The compound enhances photosynthetic rate, stomatal conductance, and nutrient uptake at very low doses.

Concentration matters. Response curves show classic hormesis: stimulation at low concentrations, no effect or inhibition at higher doses. The optimal range is crop-specific but generally falls between 0.05-20 mg/L for foliar applications. Lettuce seems to respond to much lower concentrations than tomatoes.

Environmental and genetic factors influence response magnitude. Tolerant cucumber genotypes showed larger yield improvements than sensitive ones. (3) Season, light intensity, and nutrient status affect outcomes.

Triacontanol enhances stress tolerance, particularly to salinity and drought, by improving antioxidant enzyme activity, maintaining membrane integrity, and regulating osmotic adjustment. (3) (4) This makes it especially valuable in recirculating hydroponic systems where EC can drift upward.

Practical Guidelines

• Test on a small number of plants before scaling to full production.
• Keep application rates within published ranges. More is not better with triacontanol.
• Maintain consistent spray timing rather than irregular high-dose applications.
• Store stock solutions away from light and heat to preserve activity.
• Use analytical-grade triacontanol from reputable suppliers (minimum 90% purity).
• Combine with sound nutritional management; triacontanol is not a substitute for balanced feeding. Triacontanol is not a replacement for proper nutrition, irrigation, environmental conditions or media management.

Properly formulated and applied, triacontanol provides measurable improvements in productivity and stress tolerance across major soilless crops. The citations above offer detailed protocols and results for those wishing to implement this growth regulator in commercial or research settings.

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.

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

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.

Growers often supply calcium (Ca) with calcium nitrate, but that introduces unwanted nitrogen (N). To achieve a 0% N finish in a hydroponic or soilless system (for instance to reduce residual nitrates or alter plant metabolism), an alternative Ca source is required. One option is calcium thiosulfate (CaS₂O₃), a clear, water-soluble liquid containing about 6% Ca and 10% thiosulfate sulfur. Tessenderlo Kerley’s CaTSR product is labeled 0-0-0-10S-6Ca (no N), and can replace Ca(NO₃)₂ or CaCl₂ in late-stage fertigation (zero-nitrogen) regimes.

Evidence and Discussion

Because research specifically on calcium thiosulfate (CaTS) is scarce, I evaluated what I could verify.

• A peer-reviewed article “Effects of Thiosulfate as a Sulfur Source on Plant Growth, Metabolites Accumulation and Gene Expression in Arabidopsis and Rice” studied whether plants could use thiosulfate (instead of sulfate) in hydroponic medium. The study found that both Arabidopsis (dicot) and rice (monocot) take up thiosulfate into roots, and that at modest sulfur levels (≈300 µM) rice shows similar biomass whether S is supplied as thiosulfate or sulfate. The Arabidopsis biomass was lower when thiosulfate was used above certain concentration thresholds. This shows thiosulfate is bioavailable, though with caveats depending on species, concentration and potential toxicity or metabolic cost in dicots (1).
• Another verified study “Soil Calcium Status Unrelated to Tipburn of Romaine” (Hartz et al., 2007) compared calcium nitrate, calcium thiosulfate, and calcium chloride injections via drip in field soil on romaine lettuce. They applied 17-28 kg Ca/ha in the last 1-3 weeks before harvest and found no significant improvement in leaf Ca concentration of inner leaves, nor reduction of tipburn severity, regardless of Ca source (2).
• Also, “Calcium Fertigation Ineffective at Increasing Fruit Yield and Quality of Muskmelon and Honeydew Melons in California” (Johnstone et al., 2008) compared calcium from calcium nitrate, calcium thiosulfate, and calcium chloride under drip irrigation in melon. Applications of typical industry rates of Ca via CTS or CN or Cl did not improve fruit yield, quality, or tissue Ca concentration compared to no-Ca-fertigation control (3).

So far no peer-reviewed study was found that examines Ca thiosulfate in pure hydroponic or soilless culture to replace calcium nitrate when aiming for zero N finish (apart from its use as a sulfur source). The field soil/field drip results tend to show minimal effect of late calcium injection for inner leaves or fruit quality under the tested conditions. With that said, studies have not revealed any negative effects from using calcium thiosulfate. My experience has shown no problems when using Ca thiosulfate as a zero-nitrogen Ca source at reasonable concentrations.

Implications

Given limited evidence, growers should be skeptical about expecting large gains in tissue calcium or disorder reduction simply by switching sources late in growth, especially under field or substrate conditions. However, using CaTSR is valid if your goal is to maintain calcium without adding nitrogen. Because it is soluble and delivers Ca in a bioavailable way (and provides thiosulfate that plants can absorb), it’s a workable tool in finish regimes where N must be zero or near zero.

The tradeoffs include:

• Possible metabolic cost in some species under certain S forms or concentrations
• If the calcium demand is high, source competition or diffusion limitations may still constrain uptake
• The very late supply may not change internal partitioning or yield, as many trials showed

Preparing a Stock Solution and Dosing

Here is a practical plan to use CaTSR to reach 120 ppm Ca in the final crop solution, with a 1:100 injection ratio, without introducing nitrogen:

1. Determine Ca content. CaTSR is labeled as ~6% Ca by weight (≈60 g Ca per liter if density ~1 kg/L). Confirm with product label or lab test.
2. Stock concentration target. To get 120 ppm in the working solution via 1:100 injection, the stock needs to be ~100× that: 12000 ppm Ca in stock.
3. Stock solution dilution. Since CaTSR has ~60000 ppm Ca when pure (100%), you need ~20% of that pure product in stock to get 12000 ppm. This means uou should add ~200mL/L (~750mL/gal) of stock with the rest being distilled or RO water. This should replace your normal Ca nitrate stock.
4. Injection. Use an injector that can do 1% injection (38mL/gal). That gives ~120 ppm Ca.
5. Adjustments. If the product is more dilute or denser, revise proportionally; check electrical conductivity (EC) and pH when adding CaTSR as it may shift pH or interact with other ions.

Summary

Using calcium thiosulfate (e.g. CaTSR 0-0-0-10S-6Ca) allows growers to maintain calcium levels while eliminating added nitrogen. The dilution above (~20% product in stock, injected 1:100) yields ~120 ppm Ca. Existing studies show thiosulfate is absorbed and usable (1), but field trials using CaTS late in growth often do not show improvements in tissue Ca, yield, or quality when compared to controls using other Ca sources or none (2), (3). Growers should expect moderate effects at best in substrate or field systems, unless other limiting factors are addressed.

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.

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.

Choosing the right substrate is critical in greenhouse hydroponics. Coconut coir (coco peat) has become a renewable alternative to rockwool, and recent studies show it can match or exceed rockwool in many crops. In cucumbers, switching to coir improved leaf area and marketable yield (1). In tomatoes, coir supported higher fruit yield and nutrient uptake than rockwool (2). In leafy greens, lettuce in coco peat produced more biomass than mineral wool or perlite in controlled greenhouse trials (3). Even strawberries have shown equal or better performance in coir compared to rockwool when root-zone aeration is properly managed (4).

• Tomato: Coir gave higher yields and heavier fruits than rockwool. Plants on coir had significantly greater uptake of potassium and sulfur, translating to larger fruit and more total yield (2).
• Cucumber: Coir boosted growth and yield compared to rockwool. Leaf area index and final yield were consistently higher on coir (1).
• Lettuce: Coco peat produced ~40% higher leaf biomass than perlite and ~70% higher than mineral wool in one ebb-and-flow greenhouse study (3). In another greenhouse system, rockwool gave the heaviest fresh biomass, but coir produced taller plants and longer roots (5).
• Strawberries: Over six months of pot cultivation, strawberries grown in coir matched or outperformed rockwool in shoot dry weight, while showing more stable drainage EC and pH (4). Extension reports and grower trials further suggest blends of coir with perlite improve aeration and flowering compared to pure coir (6).

Crop Comparison Table

Tomatoes on Coir vs Rockwool

In the tomato trial by Xiong et al., coir substrates significantly outperformed rockwool. Plants in coir had higher total fruit yield, greater average fruit weight, and better uptake of key nutrients such as K and S (2). This demonstrates that coir is not just a substitute but a potentially superior medium for greenhouse tomato production.

Cucumbers on Coir vs Rockwool

In greenhouse cucumbers, coir consistently gave higher vegetative vigor and fruit yield. Leaf area index and final yields were significantly higher than on rockwool (1). Nutrient analysis also showed higher Ca, Mg, and Zn contents in coir-grown plants, suggesting coir buffers nutrients more effectively.

Lettuce and Leafy Greens

In Polish greenhouse trials, coco peat lettuce heads produced substantially more leaf biomass than those grown in mineral wool or perlite (3). In contrast, a Philippine hydroponic study found rockwool produced the heaviest fresh biomass, but coco coir gave taller plants and longer roots (5). Together, these results show coir can rival or surpass rockwool, but outcomes depend on system design and cultivar.

Strawberries on Coir vs Rockwool

In Korea, a six-month hydroponic strawberry trial showed that coir matched or outperformed rockwool in shoot dry weight, while maintaining more stable EC and pH in drainage solutions (4). Practical experience also suggests that coir blended with perlite is best for strawberries, as it improves root aeration and prevents waterlogging (6). For crops that have roots that require high oxygenation, perlite amendments are fundamental to the use of coco coir for optimum results.

Coco/Perlite Blends

Many growers prefer mixing coir with perlite to improve aeration. This is especially useful for crops like strawberry, which are sensitive to low oxygen in the root zone. A 70:30 coir:perlite ratio is widely used to combine coir’s nutrient buffering with perlite’s porosity. These blends often outperform pure rockwool in practice.

Summary

Greenhouse research consistently shows that coir is a strong alternative to rockwool. Tomatoes and cucumbers perform better on coir, lettuce often produces more biomass, and strawberries grow well provided aeration is managed. Coco/perlite blends add further reliability. For growers aiming to reduce reliance on rockwool, coir and its blends represent a proven, effective option that can sustain or increase yields while offering better root-zone stability.

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.

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).

Calcium is essential yet poorly mobile in plants. Young leaves and fruit can go deficient even when solution Ca is adequate, because Ca rides the transpiration stream and is not readily redistributed. Foliar sprays target the tissues that most often lose the race for Ca. Evidence in hydroponics and soilless systems exists, but it is thinner for organic or chelated Ca forms than for simple salts. In this article I will point to some of the research on Ca foliar application, which salts work best and what dosing rates.

What the Research Shows

• Calcium chloride (CaCl₂) remains the fastest and most reliable for foliar entry. Tomato work directly comparing salts found CaCl₂ clearly superior to Ca-citrate (1).
• Calcium nitrate (Ca(NO₃)₂) is effective and less phytotoxic, but generally requires higher rates to supply the same Ca. Field potato studies showed yield and Ca increases (2).
• Sorbitol-chelated Ca has outperformed Ca(NO₃)₂ in peanuts, improving leaf Ca and yield (3).
• Calcium acetate protected rice from ozone and heat stress better than CaCl₂ at equal molar concentrations (4) (5).
• Calcium lactate improved water status and yield in lettuce under deficit irrigation (6).
• Calcium gluconate, at high concentrations, improved grape cluster quality and storability, especially when combined with chitosan (7).

Practical Rates and Outcomes

How Fast Does It Work?

• Leaf Ca increases can be measured within 1–3 days of spraying CaCl₂ (1). Expect leaf Ca rises in days, but visible symptom reduction or yield effects in 2–4 weeks of consistent spraying.
• Stress mitigation (e.g. rice under ozone) required 2 sprays but benefits were seen in yield at harvest, weeks later (4).
• Yield gains in peanut with sorbitol-Ca required repeated sprays across the season (3).

Bottom Line

• Best for quick entry: CaCl₂, 10–20 g/gal, but can be phytotoxic above ~20 g/gal. Calcium chloride will always be wet (because of how hygroscopic it is) so almost all Ca that falls and remains on leaf surfaces will eventually be taken up (unless it’s washed off).
• Good alternative: Ca(NO₃)₂, 15–25 g/gal, safer on leaves, adds nitrate.
• Organic/chelated options: Sorbitol-Ca, calcium acetate, lactate, and gluconate show benefits in specific crops and stress conditions. They often need higher mass per gallon but may reduce leaf burn or improve persistence.
• Trial first: Responses vary by crop, environment, and formulation. Test small before scaling.

Manganese is a workhorse micronutrient in plants. It is central to photosystem II, essential for the water splitting chemistry, and a cofactor for several enzymes. Given its importance, plants that produce energetically expensive compounds – like oils – might require more of it to run their machinery, so the threshold question is simple: do oilseed or essential oil crops require manganese above what non oil-producers need, or do they just need standard sufficiency with no premium for “oil production status”?

What the literature actually supports

Recent reviews agree on fundamentals. Plant Mn requirements are driven by core physiology like photosynthesis and redox balance, not by whether a crop partitions carbon to oil, starch or protein. There is no general evidence for a higher Mn setpoint in oil-producing species as a class. Instead, yield and quality respond to correcting deficiency and avoiding toxicity, the same rule that governs non oil-producing crops (1), (2).

Oilseeds

• Soybean. Classic work shows severe Mn deficiency reduces seed oil percentage. Once deficiency is corrected, pushing Mn higher does not increase oil; excess Mn depresses growth and yield. In other words, soybean needs adequate Mn, not extra because it is an oilseed (3), (4).
• Canola/rapeseed. Liming-induced Mn deficiency is common on high pH soils. Foliar Mn corrects deficiency and restores yield, but applications on adequate plants do not increase oil or seed yield. Again, the benefit is deficiency correction, not a special oil-crop premium (5).

Essential oil crops

• Water mint (Mentha aquatica). In solution culture, applying 100 µM Mn sulfate, which is ~5.5 ppm Mn, increased leaf glandular trichome density and essential oil yield relative to a lower Mn background. This shows Mn can modulate secondary metabolism when the baseline is low, but it does not prove that mint requires Mn above typical sufficiency ranges; it shows that deficiency or marginal supply limits oil yield and composition (6).
• Feverfew (Tanacetum parthenium). Varying Mg and Mn in controlled media shifted essential oil profiles. Mn interacted with Mg to alter monoterpene vs sesquiterpene proportions, again indicating composition sensitivity under limited or imbalanced supply rather than a universal need for “extra Mn” (7).

Soilless and hydroponic angle

Hydroponics removes soil redox chemistry, so Mn availability is governed by solution concentration, chelation and pH. Reviews emphasize that plants still follow the same homeostatic rules; oil status does not change the Mn target. In recirculating systems, Mn can drift due to adsorption, precipitation at higher pH and plant uptake, which explains sporadic deficiency in otherwise balanced recipes. Correct the drift and the symptoms resolve; adding more than sufficiency is unnecessary and risks toxicity, especially at low pH (1), (2).

Evidence summary

Tissue composition: are oil plants different?

Authoritative reviews catalog Mn uptake, transport and intracellular allocation across species. None propose distinct Mn sufficiency thresholds based solely on oil production. The drivers are photosynthetic demand, transporter regulation and rhizosphere chemistry. Oilseed and essential oil crops display the same deficiency symptoms and toxicity risks as other species. Practically, tissue targets should be set by species-specific sufficiency ranges and growth stage, not by “oil producer” status (1), (2).

Practical stance for soilless growers

1. Aim for sufficiency, verify with tissue tests. If chlorosis and interveinal speckling suggest Mn deficiency and tissue Mn is low, bring solution Mn up to a normal range and adjust pH. Do not chase extra Mn for oil content once sufficiency is confirmed (5).
2. Watch pH and redox. Slight pH rises or oxidizing conditions can drop available Mn even when total Mn dosing looks fine. Correct pH and renew chelates before increasing Mn concentration (1).
3. Expect composition shifts near the margins. In mint and feverfew, Mn status influenced essential oil profile when supply was marginal. That is a signal to maintain adequacy, not a license to overapply (6), (7).

Bottom line

There is no broad academic support for supplementing manganese above normal sufficiency just because a crop produces oil. The consistent finding is boring but useful: correct Mn deficiency and keep supply in a normal, pH-stable window. Oilseed yield and essential oil profiles suffer when Mn is low, and they recover when Mn is adequate. Beyond that, extra Mn does not buy more oil and can cost you growth.