Cucumber Fertilizer 8-16-36 | Chelated Micronutrients | Hydroponics, Soil & Foliar Application
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Greenway Biotech · Made in California since 1989
Cucumber Fertilizer 8-16-36.
Crisp fruit. Heavy yields.
A water-soluble 8-16-36 formula engineered for cucumbers, melons, squash, and all cucurbit vine crops. Very high potassium drives crisp, sweet fruit and shelf life; controlled nitrogen keeps vines productive without runaway foliage; six chelated and mineral micronutrients round out a complete program. CDFA-registered and independently lab tested.
Find your size → Calculate how much I need36%
Soluble potash (K₂O) — built for heavy-fruiting cucurbits
16%
Available phosphate (P₂O₅) for flowering and fruit set
100%
Water soluble — clean for drip, NFT, Dutch buckets, and foliar
6micros
Iron, manganese, zinc, copper, boron, molybdenum included
01 / Choose your size
Right-sized for the job.
Coverage assumes a typical greenhouse trellised cucumber program at ~80 plants per 100 gallons of reservoir, with weekly feeding through fruiting. Garden growers will get more weeks per bag at lighter side-dress rates.
| Bag Size | Hydroponic Reservoir Weeks | Garden Coverage | Best For |
|---|---|---|---|
| 5 lb | ~6 weeks of a 100-gal fruiting reservoir | ~400 sq ft for a full season | Backyard gardens, small greenhouses |
| 25 lb | ~33 weeks of a 100-gal fruiting reservoir | ~2,000 sq ft for a full season | Most popular |
| 55 lb | ~73 weeks of a 100-gal fruiting reservoir | ~4,500 sq ft for a full season | Best value |
02 / Ideal applications
One formula.
Every cucurbit.
All cucurbits share the same nutritional shape — heavy potassium demand at fruiting, enhanced phosphorus for flowering, controlled nitrogen to keep energy moving into fruit instead of vine.
Cucumbers
Slicing, pickling, English, Armenian, and Asian types. Works in greenhouse trellised production and outdoor field rows alike.
Melons
Cantaloupe, honeydew, watermelon, Galia, and specialty melons. High K₂O supports the sugar accumulation that drives flavor.
Squash & Pumpkins
Summer squash, winter squash, butternut, acorn, delicata, and pumpkins. Long fruit-fill window benefits from sustained K supply.
Zucchini
Green, golden, and specialty varieties. Steady potassium helps maintain firmness and shape during continuous picking.
Gourds
Decorative and edible gourds. Same vine-crop nutritional profile applies — high K₂O for fruit quality, controlled N for vine balance.
All Cucurbits
Any vine crop in the Cucurbitaceae family. If it climbs, sprawls, and sets heavy fruit on a vine, this is the right base formula.
03 / Why 8-16-36
Engineered for vine crops.
Not a generic 20-20-20.
A balanced formula spreads nutrients evenly across every stage, which is fine in theory and wrong in practice for fruiting cucurbits. This ratio is shaped around what these plants actually pull from the soil.
36%
Heavy K₂O for the heaviest demand.
Cucumbers, melons, and squash are extremely heavy potassium feeders during fruit fill. Potassium supports water regulation inside fruit cells, activates sugar-transport enzymes, contributes to cell wall strength, and helps extend post-harvest shelf life. 36% soluble potash is sized for peak demand, not average demand.
8%N
Controlled nitrogen — not too little, not too much.
Vine crops need enough nitrogen for healthy canopy, but excess N produces excessive foliage, delayed flowering, and energy diverted away from fruit. 8% N strikes the balance — adequate for healthy green growth without overcrowding the trellis or stalling fruit set.
16%P
Available phosphate that drives flowering and roots.
16% available phosphate (P₂O₅) supports the rapid energy transfer of flower induction, fruit set, and root extension. Cucurbits set continuously through the season — phosphorus has to be available continuously, not front-loaded at transplant.
100%
Truly water soluble — no clogged emitters.
Dissolves clean in cold water with no residue. Safe through drip lines, Dutch buckets, NFT channels, ebb-and-flow systems, and pressurized foliar sprayers. No filter media, no settling, no rinse-out maintenance between feedings.
6micros
Complete micronutrient package, properly chelated.
Iron, manganese, zinc, and copper are EDTA-chelated so they stay plant-available across the pH range tap water typically presents. Boron and molybdenum are supplied in highly available mineral forms — sodium molybdate and boric acid — because they don't benefit from chelation. Why chelated form matters →
CDFA
State-registered. Lab-verified. Lot-traceable.
Registered with the California Department of Food and Agriculture. Independently lab tested for heavy metal content by AgroLab/Matrix Sciences in December 2024 — results consistently well below required limits. Every bag is lot-coded, so any batch can be traced back to its production run and test certificate.
04 / The science
Why high K for vine crops.
4.5: 1 K₂O to N
Potassium-to-nitrogen ratio of 8-16-36
Potassium is the dominant nutrient pulled by fruiting cucurbits. Inside the plant, potassium regulates stomatal opening (water use efficiency under heat), activates enzymes for sugar transport from leaf to fruit, and helps maintain turgor pressure inside developing fruit cells. When potassium supply runs short during peak fruit fill, plants compensate by pulling K from older leaves into developing fruit — visible as marginal scorch on the lower canopy, often misread as a watering problem.
The 4.5:1 K₂O-to-N ratio in 8-16-36 mirrors what cucurbits actually remove from the root zone during fruiting. Balanced 20-20-20 formulas produce roughly 1:1 K to N delivery, which works for lawns and ornamental foliage and falls short for fruiting vines. The mismatch shows up as lush vines with mediocre fruit — exactly the outcome controlled-nitrogen, high-potassium formulas are designed to avoid.
The 16% available phosphate (P₂O₅) supports continuous flowering and root extension. Phosphorus moves slowly through soil, so cucurbits — which flower throughout the season rather than in one burst — benefit from a fertilizer that keeps phosphate available with every feeding, not just at transplant.
For deeper background on these nutrients, see What's the Function of Nitrogen in Plants? and What's the Function of Phosphorus in Plants?
05 / Application rates
Pick your method.
Get your rate.
Rates for cucumbers, melons, squash, and all cucurbit vine crops. Select the tab for your growing method — hydroponic reservoirs, foliar spraying, or soil and container growing.
Hydroponic Reservoirs
Quick answer: 0.5 lbs of 8-16-36 plus 500–1,000 ml of Cal-Mag Plus stock per 100 gallons during vegetative growth; bump to 0.75 lbs plus 1,000–1,500 ml at fruiting.
Rates are per 100 gallons of reservoir and assume approximately 80 plants per 100 gallons (greenhouse trellised standard). Rates assume RO or rainwater; reduce Cal-Mag Plus by 30–50% on hard tap water with measurable Ca/Mg.
| Growth Stage | 8-16-36 | Cal-Mag Plus | pH | Target EC (PPM 500 / 700) |
|---|---|---|---|---|
| Seedling | 0.25 lbs (~1.1 g per plant) |
250–500 ml | 5.8–6.2 | 1.2–1.6 EC (600–800 / 840–1120) |
| Vegetative | 0.5 lbs (~2.8 g per plant) |
500–1,000 ml | 5.8–6.2 | 1.6–2.0 EC (800–1000 / 1120–1400) |
| Flowering / Fruiting | 0.75 lbs (~4.3 g per plant) |
1,000–1,500 ml | 5.8–6.2 | 2.0–2.4 EC (1000–1200 / 1400–1680) |
RO water — Calcium Nitrate supplement: On RO or rainwater, Cal-Mag Plus alone is insufficient for fruit-set calcium during peak cucurbit production. Add Calcium Nitrate 15.5-0-0 as follows: vegetative 0.30–0.50 lbs / 100 gal; flowering / fruiting 0.50–0.75 lbs / 100 gal. Pre-dissolve Calcium Nitrate separately and add to the reservoir first.
⚠️ Calcium supplementation required: This formula contains no calcium — calcium and phosphorus are chemically incompatible in concentrated solution. Cucumbers need consistent calcium for cell wall integrity and firm fruit development. Always supplement with Cal-Mag Plus and/or Calcium Nitrate.
Mixing sequence: Fill reservoir to target volume → pre-dissolve each fertilizer separately in a small bucket of warm water → add Calcium Nitrate solution (if used) → add Cal-Mag Plus stock → add 8-16-36 solution last → adjust pH and verify EC before introducing plants. PPM readings depend on meter scale; EC is the most accurate measurement.
Foliar Spray
Quick answer: Roughly ½–1 tsp per gallon (about 2.3–4.5 g/gal) for routine maintenance sprays every 10–14 days. Cucurbit leaves are sensitive — always start at the lower end.
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. Cucurbit leaves are thinner and more sensitive to salt burn than tomato or pepper foliage. Always test on a small leaf area 24–48 hours before full application. Do not apply in direct sun, during heat or drought stress, or when temperatures exceed 85°F.
| Purpose | Per 100 gal | Per-Gallon Equivalent | Frequency |
|---|---|---|---|
| Maintenance / boost | 0.5–1 lb | ~2.3–4.5 g/gal (~½–1 tsp) | Every 10–14 days |
| Pre-bloom push | 1 lb + Cal-Mag stock 5 ml/gal in tank | ~4.5 g/gal (~1 tsp) | Once, 7–10 days before first female flowers |
| Deficiency correction | 1.5–2 lbs (MAX) | ~6.8–9 g/gal | Every 5–7 days, max 3 sprays — start at low end |
Foliar best practices: Apply early morning or late afternoon and avoid open flowers. Spray to glistening — leaves should be wet but not dripping. Cover undersides of leaves and add a non-ionic surfactant for waxy cucurbit foliage. Adjust spray solution to slightly acidic pH (~5.5–6.0) for best leaf uptake. Stop foliar feeding 7 days before harvest and rinse fruit before use. Foliar feeding supplements root feeding — it does not replace it.
Soil & Container Growing
Quick answer: 2 lbs / 100 sq ft worked in pre-plant, then 0.5 lb / 100 sq ft side-dress at vining, flowering, and fruiting. For containers, ½ tsp per gallon of soil at potting and ½ tsp per gallon of water every 2–3 weeks thereafter.
📋 Soil test first: Field crop application rates below 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. Cucurbits are heavy feeders — pre-plant organic matter significantly improves results.
| Application Method | Rate | Frequency / Timing | Notes |
|---|---|---|---|
| Pre-plant incorporation | 2 lbs / 100 sq ft | Once, before transplant | Add generous compost; cucurbits are heavy feeders |
| Side-dress — vining | 0.5 lb / 100 sq ft | When vines start to run | Band 4–6" from stem |
| Side-dress — flowering | 0.5 lb / 100 sq ft | At first female flower | Band 4–6" from stem |
| Side-dress — fruiting | 0.5 lb / 100 sq ft | At first fruit set | Pair with separate Ca/N program |
| Drip fertigation | 0.75 lb / 100 gal | Weekly during fruiting | Use 25–50% of rate for continuous fertigation |
| Container — at potting | 0.5 tsp / gallon of soil volume | Once at potting | Mix thoroughly into media |
| Container liquid feed | 0.5 tsp / gallon water | Every 2–3 weeks | Top-dress monthly with dry application |
| Soil drench — seedling | 0.25 lb / 100 gal | At transplant | — |
| Soil drench — vegetative | 0.5 lb / 100 gal | Weekly | — |
| Soil drench — fruiting | 0.75 lb / 100 gal | Weekly | Pair with separate Ca/N program |
| Per acre (field reference) | 200–400 lbs | Split applications | Base on current soil test and crop removal — consult local extension |
Soil supplement pairing: Gypsum (CaSO₄) at 3 lbs / 100 sq ft pre-plant provides calcium without changing pH. Use Epsom Salt only if a soil or tissue test confirms magnesium deficiency — container and coco media may need routine Mg supplementation. Calcium Nitrate as a side-dress at 0.25 lb / 100 sq ft monthly during fruiting can help on arid or sandy soils.
06 / How to use & calculate
Dissolve.
Feed.
Harvest.
Four steps and a calculator that matches your grow. Pick the tab that matches your growing method and feed on the schedule your stage calls for.
-
01
Pre-dissolve, never dry-mix
Always dissolve 8-16-36 in warm water in a separate container before adding it to a reservoir, drench, or sprayer. Dry-mixing with other fertilizers can produce inconsistent ratios; pre-dissolving guarantees you get the full rate every time.
-
02
Add Cal-Mag first, then 8-16-36
In hydroponic mixing, calcium and concentrated phosphate will precipitate as white cloudiness if combined directly. Add Cal-Mag Plus (or pre-dissolved Calcium Nitrate) first and stir thoroughly, then add the 8-16-36 solution. Adjust pH after both are fully dispersed.
-
03
Feed on the schedule your stage calls for
Seedlings and vegetative plants need lighter EC; flowering and fruiting plants need the full rate plus calcium support. Use the Application Rates tables for exact stage rates, then dial in by watching EC, runoff, and plant response.
-
04
Hold back near harvest
Stop foliar feeding 7 days before harvest and rinse fruit before use. In soil, taper or skip the last scheduled side-dress as final fruit ripens. This is general practice, not crop failure insurance — flavor and shelf life benefit from a clean finish.
07 / Compare
Crop-specific formulas.
Different jobs.
All four of our crop-specific water-soluble formulas share the same chelated-micronutrient backbone. The macronutrient ratios are tuned to the demand profile of each crop family.
| Product | NPK | K₂O : N Ratio | Best For | Notes |
|---|---|---|---|---|
| Cucumber Fertilizer 8-16-36 (this product) | 8-16-36 | 4.5 : 1 | All cucurbits — cucumbers, melons, squash, pumpkins, zucchini, gourds | Controlled N for trellised vines; high K for fruit quality |
| Tomato Fertilizer 4-18-38 | 4-18-38 | 9.5 : 1 | Fruiting nightshades — tomatoes, peppers, eggplant | Lower N and higher K than 8-16-36; ideal once nightshades are flowering |
| Pepper & Herb 11-11-40 | 11-11-40 | 3.6 : 1 | Peppers, basil, herbs, and crops needing balanced N–P with very high K | Higher N than tomato or cucumber formulas; supports pepper canopy |
| Strawberry Fertilizer 8-12-32 | 8-12-32 | 4.0 : 1 | Strawberries, brambles, small berry crops | Tuned to berry brix and runner management |
| Lettuce Fertilizer 8-15-36 | 8-15-36 | 4.5 : 1 | Lettuce, leafy greens, herbs grown for foliage | Similar ratio to cucumber but tuned for tip-burn resistance in leafy crops |
08 / Decision
Is 8-16-36 the right
formula for you?
8-16-36 is purpose-built for one job: fruiting cucurbits at the stage when potassium demand peaks. It's an excellent fit for that. It's not the right base formula for every crop or every stage.
Best Choice For
- Cucumbers, melons, squash, pumpkins, zucchini, gourds — any cucurbit vine crop
- Fruiting and ripening stage when potassium demand peaks
- Hydroponic systems needing 100% water-soluble nutrition
- Greenhouse cucumber production at any scale
- Container and raised-bed growers who want predictable, water-soluble feeding
- Drip-fertigated outdoor cucurbit fields
Consider Another Product If
- You're growing tomatoes, peppers, or eggplant — try Tomato Fertilizer 4-18-38 for higher K and lower N tuned to nightshades
- You're growing strawberries or other berries — try Strawberry Fertilizer 8-12-32
- You're growing lettuce, leafy greens, or herbs — try Lettuce Fertilizer 8-15-36
- You're in seedling or early vegetative stage only — consider a more balanced formula like Grow Green 4-2-6 until flowering begins
- You need calcium in the same formula — 8-16-36 contains no calcium by design (Ca + P precipitate); pair with Cal-Mag Plus instead
09 / Build the program
8-16-36 is the base.
These complete the program.
A vine-crop feeding program needs calcium, magnesium, and a way to push extra potassium during peak fruiting. These pair-products fill the gaps 8-16-36 deliberately leaves open.
Essential
Cal-Mag Plus 2-0-0
Supplies the calcium cucumbers need for cell wall integrity and firm fruit development. Mandatory companion in hydroponic systems and recommended in soil — apply separately from 8-16-36 to avoid precipitation.
RO waterCalcium Nitrate 15.5-0-0
An additional calcium source for RO and rainwater hydroponic systems where Cal-Mag Plus alone can fall short during peak fruit set. Provides a small nitrate-N boost too.
MagnesiumEpsom Salt (Magnesium Sulfate)
Magnesium support for chlorophyll production. Useful when soil or tissue testing indicates Mg deficiency, particularly in containers, coco media, and sandy soils.
Peak fruitPotassium Sulfate 0-0-53
A targeted potassium boost during peak fruiting weeks if EC or tissue testing suggests K is the limiting nutrient. Use sparingly — most programs don't need it.
10 / Safety & handling
Read this before
you mix.
Standard handling for a water-soluble specialty fertilizer. See the linked SDS for complete first aid and storage detail.
- Wear gloves and eye protection when handling dry powder or concentrated solutions. Avoid inhaling dust — use in well-ventilated areas or wear a dust mask when measuring. Wash hands thoroughly after handling.
- Store in a cool, dry place in the original sealed container. Product is hygroscopic and will absorb moisture from the air if exposed. If powder clumps from moisture exposure, break it up — efficacy is not affected. Keep away from children and pets.
- Do not apply foliar sprays during peak sun hours or when temperatures exceed 85°F. Avoid direct contact with plant stems and foliage when applying to soil; water in thoroughly after soil application to prevent root burn.
- Never combine calcium sources (Cal-Mag Plus, Calcium Nitrate) with concentrated 8-16-36 in the same stock tank — calcium phosphate precipitate forms and nutrients become unavailable. Always pre-dissolve separately and add in the documented mixing order. Boron: apply only to crops listed on the product label. Molybdenum: do not apply to forage or pasture crops — elevated molybdenum in forage is toxic to ruminant animals.
- First aid: Eye contact — flush with clean water for 15 minutes; seek medical attention if irritation persists. Skin contact — wash with soap and water. Ingestion — do not induce vomiting; contact Poison Control (1-800-222-1222) or seek medical attention. Inhalation — move to fresh air; seek medical attention if symptoms persist. Refer to the Safety Data Sheet (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?
Cucumbers are extremely heavy potassium feeders during fruit fill. Potassium supports water pressure inside fruit cells, activates enzymes that move sugars from leaf to fruit, and contributes to cell wall strength and firmness. Adequate potassium can also help reduce the stress conditions that sometimes contribute to cucurbitacin accumulation and bitterness — though bitterness in cucumbers is also influenced by genetics, heat, irregular watering, and overall plant stress. 36% soluble potash is sized for peak demand rather than average demand, so plants have what they need at the moment of heaviest pull.
What pH should I maintain for cucumbers?
In hydroponic systems, keep pH between 5.8 and 6.2 across all stages. In soil, aim for 6.0–6.5. pH directly governs nutrient availability — outside these ranges, key nutrients like iron and phosphorus become locked out even when present in solution. For a deeper look at how pH interacts with nutrient uptake, see Sulfate vs Chelated Fertilizers.
How do I prevent bitter cucumbers?
Cucumber bitterness is caused by cucurbitacin compounds that accumulate mainly in response to plant stress — heat, irregular watering, poor nutrition, and variety genetics all play a role. Good nutrition can help reduce one of those stressors:
- Adequate potassium supports water balance within fruit cells
- Controlled nitrogen helps avoid excessive vine stress
- Balanced micronutrients help reduce the overall stress load that can trigger cucurbitacin production
Combine good nutrition with consistent watering (avoid letting plants dry out), choose low-bitterness varieties where available, and supplement with Cal-Mag Plus during fruit development. No fertilizer can fully offset varietal genetics or severe environmental stress.
Can I use this for greenhouse cucumber production?
Yes — greenhouse trellised cucumbers are the standard reference profile for these rates. Use 0.25 lbs / 100 gal for seedlings, 0.5 lbs for vegetative, and 0.75 lbs for fruiting. Monitor EC closely — greenhouse plants under sustained light pressure can be more sensitive to EC drift than outdoor plants. Increase Cal-Mag support during rapid growth periods and adjust based on variety (European seedless types typically run higher EC than standard slicing types).
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 16% available phosphate (P₂O₅), calcium has to be supplied separately. Cucumbers need consistent calcium for cell wall integrity and firm fruit development — use Cal-Mag Plus 2-0-0 and/or Calcium Nitrate 15.5-0-0 as companions throughout the season.
How do I store the powder?
The fertilizer is 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 — efficacy is not affected. For long-term storage, double-bag inside a sealed plastic tub.
Can I use this on watermelons and cantaloupes?
Yes. This formula works for all cucurbit crops including watermelons, cantaloupes, honeydew, squash, pumpkins, and gourds. All cucurbits share similar nutritional needs — high potassium for fruit quality, enhanced phosphorus for flowering, and controlled nitrogen to avoid excessive vine growth at the expense of fruit. Apply at the standard cucumber rates listed in the Application Rates tables.
Is the formula OMRI listed or organic?
No. Cucumber Fertilizer 8-16-36 is a synthetic water-soluble specialty fertilizer formulated from solution-grade mineral salts — not an OMRI-listed organic input. It's CDFA registered and independently lab tested. Growers who need OMRI-listed inputs should look at Bone Meal, Blood Meal, and other organic amendments instead.
Ready to feed?
Pick your bag. We'll ship it.
From 5 lb home-garden bags to 55 lb commercial sacks. Orders over $100 ship free, and every bag is backed by our 90-day money-back guarantee. If 8-16-36 doesn't perform on your cucumbers, send back the unused portion for a full refund.
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