Lettuce Fertilizer 8-15-36 | Chelated Micronutrients | Hydroponics, Soil & Foliar Application
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Greenway Biotech · Made in California since 1989
Lettuce Fertilizer 8-15-36.
Engineered for leafy greens.
A premium water-soluble formula built specifically for lettuce, kale, spinach, chard, and all leafy crops. High potassium can significantly improve crisp texture and shelf life, while EDTA-chelated micronutrients support deep green color across soil, hydroponic, and foliar growing. CDFA registered and third-party lab tested.
Find your size → Calculate how much I need36%
Soluble potash (K₂O) for crisp texture & shelf life
8%
Moderate nitrogen — flavor over excess succulence
6chelated
Complete micronutrient package, EDTA where it counts
100%
Water soluble — drip, NFT, DWC, aero, foliar
01 / Choose your size
Right-sized for the job.
Coverage estimates assume the standard hydroponic vegetative rate (0.4 lb / 100 gal reservoir) or container liquid feed (½ tsp / gal water, every 10 days). Actual usage varies with crop stage, plant density, and source-water EC.
| Bag Size | Hydroponic Reservoirs | Container Feeds | Best For |
|---|---|---|---|
| 2 lb | ~225 gal of solution | ~180 single-gallon feedings | Home growers, small NFT systems |
| 5 lb | ~560 gal of solution | ~450 single-gallon feedings | Most popular |
| 25 lb | ~2,800 gal of solution | ~2,250 single-gallon feedings | Best value |
02 / Ideal applications
One bag.
Every leafy crop.
Engineered nutrient ratios for the entire leafy-green family — lettuce, brassicas, baby leaf, and microgreens included. Scale down for baby leaf and microgreen production.
Lettuce
Romaine, iceberg, butterhead, leaf, and baby mix — both soil and hydroponic production.
Spinach
Baby and mature savoy types. The moderate nitrogen profile can help reduce excess oxalate accumulation.
Kale & Collards
Curly, lacinato, red Russian, and collard greens — soil and hydroponic.
Bok Choy & Cabbage
Napa, green, red, and pak choi varieties. The high-K profile may support firm head formation.
Arugula & Chard
Rocket, Swiss chard, and rainbow chard. Excellent for cut-and-come-again production.
Microgreens & Baby Leaf
Scale to quarter or half strength for fast-turnover crops. A single low-EC feeding usually suffices.
03 / Why 8-15-36
Built for leafy crops.
Not a general-purpose blend.
The 8-15-36 ratio is engineered for the unique nutritional demands of lettuce and leafy greens — where leaf quality, texture, and shelf life are the goals, not bulk vegetative mass.
36%
High potassium for crisp texture.
Soluble potash (K₂O) can help strengthen cell walls for the crunch consumers expect, and may support extended post-harvest shelf life. Learn more in What's the Function of Potassium in Plants?
8%
Moderate nitrogen, on purpose.
Excess nitrogen creates overly succulent tissue with reduced shelf life, bitter flavors, and elevated nitrate accumulation. 8% provides enough N for healthy chlorophyll and leaf development — without the downsides. See What's the Function of Nitrogen in Plants?
6chelated
Complete micronutrient package.
All six essential micronutrients in precise ratios. Iron, manganese, zinc, and copper are EDTA-chelated to stay available at higher pH; boron and molybdenum are supplied in highly available mineral forms. See Sulfate vs. Chelated Fertilizers.
100%
Water soluble — every system.
Dissolves readily in cold water with zero residue. Suitable for drip lines, NFT channels, DWC, aeroponics, and fine-mist foliar sprayers when used at recommended concentrations. See What Are the Best Fertilizers for Hydroponics?
CDFA
Registered, lab-tested, traceable.
Registered with the California Department of Food and Agriculture. Each batch is tested for heavy metals by an independent lab — results consistently well below required limits. Documents available below.
04 / The science
Why leafy greens are heavy K feeders.
36% K₂O
Soluble potash from MKP, potassium sulfate & potassium nitrate
Leafy greens are largely water — and potassium is the nutrient that controls water pressure inside plant cells (turgor pressure). The 36% K₂O level in this formula reflects the heavy potassium demand of crops where the leaf itself is the product. Potassium regulates stomatal function and water-use efficiency, activates over 60 enzyme systems, and can help strengthen cell walls for the crisp texture buyers expect.
The nitrogen is supplied as 7.5% nitrate and 0.5% ammoniacal. The predominantly nitrate form is directly available for rapid uptake; the small ammoniacal fraction helps moderate root-zone pH in higher-alkalinity water. The available phosphate (P₂O₅) at 15% develops strong root systems for maximum nutrient uptake, supports ATP production for cellular energy, and promotes faster establishment.
Iron, manganese, zinc, and copper are EDTA-chelated so they remain soluble across a wide pH range — particularly important in alkaline irrigation water or high-pH growing media, where unchelated mineral forms can precipitate before reaching plant roots. Boron and molybdenum don't form the same insoluble compounds and are supplied in highly available mineral forms.
For deeper coverage, see What's the Function of Potassium in Plants? and What's the Function of Phosphorus in Plants?
05 / Application rates
Pick your method.
Get your rate.
Recommended starting rates for lettuce, kale, spinach, chard, and all leafy crops. Adjust based on plant size, growth stage, and source-water EC. Hydroponic rates assume RO or rainwater — reduce Cal-Mag Plus by 30–50% for tap water with 30+ ppm calcium.
Hydroponic Production
Quick answer: 0.3–0.5 lb of 8-15-36 per 100 gal during vegetative growth at 1.2–1.6 EC, pH 5.6–6.0. Pair with Cal-Mag Plus.
| Growth Stage | 8-15-36 | Cal-Mag Plus Stock* | pH | Target EC |
|---|---|---|---|---|
| Seedling / Transplant | 0.15–0.25 lbs | 250–500 ml | 5.8–6.2 | 0.8–1.0 EC |
| Vegetative | 0.3–0.5 lbs | 500–1,000 ml | 5.6–6.0 | 1.2–1.6 EC |
| Mature / Harvest | 0.4–0.5 lbs | 1,000 ml | 5.5–6.0 | 1.4–1.8 EC |
*Cal-Mag stock: prepared by dissolving the full 5 lb bag in 2 gallons of water. All ml values above refer to that prepared liquid stock — not dry powder. Shake before each use.
⚠ Do not exceed 2.0 EC for lettuce. Higher EC significantly increases tip burn risk. PPM/TDS readings depend on meter scale — EC is the most accurate measurement. 500-scale: PPM = EC × 500; 700-scale: PPM = EC × 700.
Hard water (30+ ppm Ca): reduce Cal-Mag Plus stock by 30–50%. Above 80 ppm Ca, Cal-Mag may not be needed at seedling/vegetative stages — test source water first.
Sources: Resh, "Hydroponic Food Production" (CRC Press, 7th ed.); Cornell CEA Lettuce Handbook; UMass Amherst Center for Agriculture, Food & Environment greenhouse lettuce guidance. Rates aligned to Greenway Biotech Application Rates Master Reference v3.1 §7.
Tip burn & plant density: Rates assume ~120 plants per 100 gallons (NFT/raft standard, 1.2 plants/gal). Scale proportionally for denser or sparser plantings. Tip burn is a calcium-transport issue triggered by rapid growth at high EC, low humidity, and poor air movement — not a deficiency foliar feeding can fix. Prevention: keep EC under 1.8 during head fill, maintain root-zone Ca, ensure canopy air movement, and avoid leaf temperatures above 75°F during head fill.
Foliar Spray (Supplemental)
Quick answer: 0.5 lb per 100 gal (~½ tsp per gallon) for supplemental Ca/Mg support during head fill — stop all foliar feeding 7 days before harvest.
⚠ Stop foliar feeding 7 days before harvest. Fertilizer residue on leaves is unacceptable for fresh consumption or retail sale. For cut-and-come-again, apply only immediately after a harvest cycle — not during head fill. Test on a small area and wait 24 hours before full application. Apply early morning or late afternoon only — never above 80°F leaf temperature.
| Purpose | 8-15-36 Rate | Cal-Mag Stock | Frequency / Notes |
|---|---|---|---|
| Supplemental Ca/Mg support | 0.5 lb / 100 gal (~½ tsp/gal) | 10 ml/gal in tank | Weekly during head fill — supplemental only, not a tip-burn cure |
| Maintenance / general | 0.25–0.5 lb / 100 gal | 5 ml/gal in tank | Every 10 days; light spray to glistening, not runoff |
| Deficiency correction (MAX) | 0.75 lb / 100 gal | — | Every 5–7 days, max 2 sprays — then address root-zone nutrition |
Foliar safety check: Foliar rates should be well below soil rates — typically 1–4 g/gallon (or 2–6 g/liter) depending on crop sensitivity. Always test on a small area first, spray in early morning or late afternoon, and avoid spraying in temperatures above 85°F.
Per-gallon conversion: 0.25 lb / 100 gal ≈ 1.1 g/gal (~¼ tsp/gal); 0.5 lb / 100 gal ≈ 2.3 g/gal (~½ tsp/gal); 0.75 lb / 100 gal ≈ 3.4 g/gal (~¾ tsp/gal). Teaspoon equivalents are approximate (~4.5 g/tsp) — weigh for precision.
Sources: UMass Amherst Extension foliar feeding guidance for greenhouse leafy greens; Cornell CEA Lettuce Handbook; Resh, "Hydroponic Food Production" (CRC Press, 7th ed.). Do not combine Cal-Mag Plus concentrate with 8-15-36 concentrate — mix each separately into the diluted spray tank.
Soil, Container & Drench Application
Quick answer: 1–3g per plant every 2–4 weeks, or ½ tsp per gallon as a container liquid feed every 10 days. Supplement with Cal-Mag Plus separately.
| Application Method | Rate | Timing |
|---|---|---|
| Per plant (any soil method) | 1–3g per plant (~¼–½ tsp) | Every 2–4 weeks; 1g for seedlings, 3g for active growth, 5g for large heads |
| Pre-plant incorporation | 1 lb / 100 sq ft + 2" compost | Once, before transplant or direct seeding |
| Side-dress (cut-and-come-again) | 0.25 lb / 100 sq ft | Every 2 weeks during active growth |
| Side-dress (head lettuce) | 0.25 lb / 100 sq ft | Single application at heading; reduce 2 weeks before harvest |
| Drip fertigation | 0.5 lb / 100 gal | Weekly during active growth |
| Container — at potting | ½ tsp per gallon of soil volume, mixed in | At potting; top-dress at 3 weeks |
| Container — liquid feed | ½ tsp per gallon water | Every 10 days during active growth |
| Soil drench (seedling) | 0.125–0.25 lb / 100 gal | At transplant |
| Soil drench (vegetative) | 0.25–0.5 lb / 100 gal | Weekly; reduce 2 weeks before harvest |
⚠ Calcium supplementation: This formula does not contain calcium because calcium and phosphorus should not be mixed in a concentrated stock solution — they can form insoluble calcium phosphate. Use separate stock tanks for calcium fertilizers and other concentrated fertilizer salts. Always dilute each independently before combining in the main tank. Supplement with Cal-Mag Plus or Calcium Nitrate separately. Tip burn in lettuce is a calcium transport issue — consistent moisture and moderate EC matter as much as calcium availability.
📋 Soil test first: Field-crop application rates above are general guidelines based on typical soil-test levels and crop removal estimates. Actual rates should be confirmed by a current soil test and consultation with your local cooperative extension service, as needs vary significantly by soil type, crop variety, and regional conditions.
Sources: University of California Agriculture & Natural Resources (UC ANR) lettuce production guidelines; UMass Amherst Extension vegetable production guide; Cornell CEA Lettuce Handbook; Greenway Biotech Application Rates Master Reference v3.1 §7.
06 / How to use & calculate
Dissolve.
Measure.
Feed.
8-15-36 dissolves readily in cold water. Use the calculator for exact amounts in any system, and follow the mixing-order rules to avoid precipitation.
-
01
Pre-dissolve each fertilizer separately
Each product goes into its own small bucket of water before adding to the reservoir or watering can. Never combine concentrates dry or directly — calcium and phosphate sources will precipitate. See Best Fertilizers for Hydroponics.
-
02
Mix in the right order
Add Calcium Nitrate solution first (if using on RO water) — stir. Add Cal-Mag Plus stock next — stir. Add the dissolved 8-15-36 last and stir until fully dispersed.
-
03
Adjust pH and verify EC
Target pH 5.8–6.2 for seedlings, 5.6–6.0 for vegetative, 5.5–6.0 for mature plants. Do not exceed 2.0 EC for lettuce — higher EC significantly increases tip burn risk. Replace recirculating solutions every 7–14 days.
-
04
Stop foliar feeding 7 days before harvest
Fertilizer residue on leaves is unacceptable for fresh consumption or retail. Apply foliar only early morning or late afternoon — leaf temperature below 80°F. Test small area first and wait 24 hours before full application.
07 / Compare
8-15-36 vs other
Greenway crop blends.
Crop-specific blends are tuned to the unique nutrient demands of each plant family. Here's how 8-15-36 compares to our other water-soluble crop formulas. For broader comparisons, see Best Fertilizers for a Vegetable Garden.
| Product | NPK | Best Crop | Key Trait | Form |
|---|---|---|---|---|
| Lettuce Fertilizer 8-15-36 (this product) | 8-15-36 | Leafy greens | High K, moderate N — texture & shelf life | Water-soluble powder |
| Tomato Fertilizer 4-18-38 | 4-18-38 | Tomatoes & nightshades | Highest K, low N — fruit set & finish | Water-soluble powder |
| Pepper & Herb 11-11-40 | 11-11-40 | Peppers, woody herbs | Balanced NPK with very high K | Water-soluble powder |
| Cucumber Fertilizer 8-16-36 | 8-16-36 | Cucumbers, melons, vining crops | Tuned for vine crop fruit fill | Water-soluble powder |
| Strawberry Fertilizer 8-12-32 | 8-12-32 | Strawberries, small berries | Optimized berry nutrition profile | Water-soluble powder |
08 / Decision
Is this the right
fertilizer for you?
8-15-36 is engineered for leafy crops. For tomatoes, peppers, vining crops, or berries, a crop-specific blend will fit better.
Best Choice For
- Growing any leafy green — lettuce, kale, spinach, chard, bok choy, arugula, collards
- Leafy culinary herbs (basil, cilantro, parsley, mint, dill) — use at slightly lower EC than lettuce
- Hydroponic systems for leafy crops — NFT, DWC, ebb and flow, aeroponics
- Microgreen and baby leaf production at reduced concentration
- Commercial greenhouse lettuce at any scale
- Soil, container, and raised-bed leafy green production
Consider Another Product If
- Growing tomatoes or peppers — try Tomato Fertilizer 4-18-38 instead
- Growing cucumbers or melons — try Cucumber Fertilizer 8-16-36 instead
- Growing strawberries — try Strawberry Fertilizer 8-12-32 instead
- Growing woody Mediterranean herbs — try Pepper & Herb 11-11-40 instead
09 / Build the program
8-15-36 is the base.
These complete the program.
Calcium must be supplied separately. Add iron or potassium boosts where the crop or system calls for it.
Essential
Cal-Mag Plus 2-0-0
Calcium and magnesium for tip-burn-prone leafy crops. Commonly paired with 8-15-36 in hydroponic lettuce production.
AlternativeCalcium Nitrate 15.5-0-0
Another calcium source with a small nitrogen boost. Useful for RO-water hydroponic head-fill production.
Color boostChelated Iron EDTA 13%
Extra iron for deep green color when pH or alkalinity is locking out the base Fe in 8-15-36.
Quality finishPotassium Sulfate 0-0-53
Additional potassium for improved texture and extended shelf life in the final weeks before harvest.
10 / Safety & handling
Read this before
you mix.
Standard PPE applies. Watch the mixing order. Stop foliar 7 days before harvest. Full SDS linked below.
- Wear gloves and eye protection when handling dry powder or concentrated solutions. Use a dust mask when measuring in confined spaces.
- Store in a cool, dry place in the original sealed container — the powder is hygroscopic and will absorb moisture if exposed. If it clumps, break it up; efficacy is not affected.
- Use separate stock tanks for calcium fertilizers and other concentrated fertilizer salts. Always dilute each independently before combining in the main tank, and jar-test unfamiliar combinations before injecting.
- Apply only to crops listed on the label. Boron can injure sensitive crops at elevated rates. Do not apply to forage or pasture crops without confirming baseline Mo levels — elevated Mo can affect ruminant animals.
- Eyes: flush with water for 15 minutes. Skin: wash with soap and water. Ingestion: do not induce vomiting — contact Poison Control (1-800-222-1222). Inhalation: move to fresh air. Refer to the SDS for complete safety information.
11 / FAQ
Common questions.
Honest answers.
If your question isn't here, contact our team at questions@greenwaybiotech.com.
Why is the potassium (36%) so high in this formula?
Leafy greens are largely water, and potassium is the nutrient that controls water pressure inside plant cells (turgor pressure). The 36% soluble potash (K₂O) can help support cell-wall thickness for that perfect crunch, resistance to wilting under grow lights, and post-harvest quality. Without adequate potassium, lettuce tends to become limp and can lose market value more quickly. For a deeper look, see What's the Function of Potassium in Plants?
What pH should I maintain for lettuce?
Lettuce is particularly sensitive to pH. If pH is too high, iron locks out (causing yellow leaves). If too low, calcium locks out (contributing to tip burn). For hydroponics, keep pH between 5.8–6.2 for the best balance. In soil, aim for 6.0–6.5. Check pH daily in hydroponic systems — lettuce responds quickly to pH drift. For a full guide to yellowing leaves and nutrient lockout, see 8 Reasons Why Plant Leaves Turn Yellow.
Will this fix tip burn on my lettuce?
Tip burn is a calcium-transport issue — calcium isn't reaching the fast-growing inner leaves quickly enough. This fertilizer does not contain calcium because calcium and phosphorus are chemically incompatible in the same concentrated solution. You must supplement with Cal-Mag Plus or Calcium Nitrate. The balanced 8-15-36 formula may help by keeping nitrogen moderate (which can reduce excessive growth rate) and providing high potassium (which supports calcium transport within the plant). Airflow, cultivar, humidity, and growth rate also influence tip burn risk — nutrition is one part of a complete management approach.
Can I use this for baby leaf and microgreen production?
Yes. For baby leaf (3–4 weeks to harvest), use at 50–75% of standard concentration, apply every 5–7 days, and target EC of 0.8–1.2. For microgreens (7–14 days to harvest), use at 25% concentration after cotyledons emerge — a single application is usually sufficient with a target EC of 0.4–0.6.
Why doesn't this fertilizer contain calcium?
Calcium and phosphorus are chemically incompatible in concentrated solution. When mixed, they form insoluble calcium phosphate that precipitates out and becomes unavailable to plants. Since this formula contains 15% available phosphate (P₂O₅), calcium must be applied separately. Use Cal-Mag Plus 2-0-0 or Calcium Nitrate 15.5-0-0 as a companion product.
Why are the micronutrients EDTA-chelated?
Iron, manganese, zinc, and copper are EDTA-chelated so they remain soluble and plant-available across a wide pH range — particularly in alkaline irrigation water or high-pH growing media, where unchelated mineral forms can precipitate and lock up before reaching plant roots. Boron and molybdenum don't form the same insoluble compounds and are supplied in highly available mineral forms. For a full comparison, see Sulfate vs. Chelated Fertilizers.
How do I store the powder?
This fertilizer is highly hygroscopic, meaning it absorbs moisture from the air. Keep the bag sealed tight between uses and store in a cool, dry place out of direct sunlight. If it clumps from moisture exposure, simply break it up — the efficacy is not affected.
What's the role of nitrogen at only 8% for leafy greens?
You might expect a leafy green fertilizer to have very high nitrogen, but too much creates problems: overly succulent tissues prone to disease, reduced shelf life, bitter flavors, and increased nitrate accumulation in leaves. The 8% provides enough nitrogen for healthy chlorophyll production and leaf development without those downsides. For more on nitrogen's role in plant biology, see What's the Function of Nitrogen in Plants?
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Available in 2 lb, 5 lb, and 25 lb sizes. Free shipping on orders over $100. Backed by our 90-day money-back guarantee — if it doesn't work for your crop, send the unused portion back for a full refund.
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