FREE SHIPPING ON ALL ORDERS OVER $100 (CONTINENTAL US ONLY!)

Cucumber Fertilizer 8-16-36 | Chelated Micronutrients | Hydroponics, Soil & Foliar Application

Regular Price
$ 24.99
Sale Price
$ 24.99
Regular Price
$ 24.99
Sold Out
Unit Price
per 

Weight: 1 Pound

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 need

36%

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 with weekly feeding through fruiting. Garden growers feeding by area will get more weeks per bag at lighter side-dress rates.

Cucumber Fertilizer 8-16-36 coverage by bag size
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: Feed by the plant — 1.4 g of 8-16-36 per plant at vining, 2.8 g at flowering, 4.2 g at fruiting. Dose Cal-Mag Plus and Calcium Nitrate per gallon, then adjust water to land your final measured EC in the cucumber range.

Amounts are per plant and stay fixed at any reservoir size — water volume only sets concentration. Cal-Mag Plus and Calcium Nitrate are dosed per gallon so final EC stays safe. The EC column is the final measured value after all nutrients are mixed, not the 8-16-36 fraction alone. Calcium Nitrate applies to RO or soft water only.

Hydroponic application rates — Cucumber Fertilizer 8-16-36, per plant with per-gallon companions
Growth Stage 8-16-36 (per plant) Cal-Mag Plus Calcium Nitrate (RO/soft only) Water per Plant Final EC pH
Vining / Seedling 1.4 g (¼ tsp) 5 ml/gal 1.5–2.0 g/gal 0.9–1.1 gal 1.5–1.8 EC 5.8–6.2
Flowering 2.8 g (½ tsp) 10 ml/gal 2.3–2.7 g/gal 1.3–1.5 gal 2.1–2.5 EC 5.8–6.2
Fruiting 4.2 g (¾ tsp) 10 ml/gal 2.3–2.7 g/gal 1.9–2.1 gal 2.2–2.6 EC max 5.8–6.2

⚠️ Do not omit Calcium Nitrate at fruiting in RO or soft water. This formula contains no calcium — calcium and phosphate are chemically incompatible in concentrated solution — and fruiting is peak calcium demand for firm fruit and cell-wall integrity. In RO or soft water, keep Calcium Nitrate 15.5-0-0 in the reservoir from vining onward.

Mixing sequence: Fill to full water volume → dissolve Calcium Nitrate fully → add Cal-Mag Plus → add 8-16-36 last → adjust pH to 5.8–6.2 and verify final EC. Never combine concentrated calcium products directly with concentrated phosphate or sulfate fertilizers.

Hard tap water: use a water report. If starting water is above roughly 0.5 EC or already carries measurable calcium and magnesium, reduce Cal-Mag Plus and Calcium Nitrate accordingly. On pure RO, magnesium can run below the cucumber target — add a magnesium source only if water or tissue testing shows a deficiency.

Foliar Spray

Quick answer: A scant ¼ teaspoon (max 1 g by weight) of 8-16-36 per plant in at least 1 quart of water, every 10–14 days. Cucurbit leaves burn easily — measure light and never exceed 4.5 g per gallon.

Foliar safety check: Concentration is capped for burn-sensitive cucurbit foliage, which is thinner and more salt-sensitive than tomato or pepper leaves. The 1 g per quart rate equals 4 g per gallon, safely under the 4.5 g per gallon ceiling. A full level ¼ teaspoon weighs about 1.4 g, which would push a 1-quart mix over the limit — so keep the scoop scant or weigh it. Always test on a small leaf area 24–48 hours first. Do not apply in direct sun, during heat or drought stress, or above 85°F.

Foliar application rates — Cucumber Fertilizer 8-16-36, per plant
Stage Per Plant Minimum Water Frequency
Vining Scant ¼ tsp (max 1 g) 1 qt Every 10–14 days
Flowering Scant ¼ tsp (max 1 g) + Cal-Mag Plus 1.25 ml 1 qt Every 10–14 days
Fruiting Scant ¼ tsp (max 1 g) 1 qt Every 7–10 days
Deficiency correction (any stage) 2 g maximum 2 qt minimum Every 5–7 days, max 3 sprays

Foliar best practices: Apply early morning or late afternoon and avoid open flowers. Spray to glistening — leaves wet but not dripping. Cover leaf undersides 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: This is a supplemental high-potassium feed, not a complete program — pair it with compost, a nitrogen source, and calcium. In the ground, dose by area: about 105 g (3.7 oz) per 100 sq ft worked in pre-plant, then side-dress at vining, flowering, and fruiting. In containers, feed by plant on the schedule below.

📋 Supplemental feed — plan nitrogen separately: 8-16-36 is a low-nitrogen, high-potassium supplement. Across a full season the soil program supplies roughly 385 g (13.6 oz) of product per 100 sq ft — strong on potassium but light on nitrogen, so add a separate nitrogen plan such as a balanced pre-plant fertilizer plus a nitrogen side-dress after bloom, guided by a current soil test. Soil is dosed by area; containers by plant.

Soil and container application rates — Cucumber Fertilizer 8-16-36
Stage Soil (per 100 sq ft) Container (per plant)
Pre-plant ~105 g (3.7 oz), worked in 2.8 g (½ tsp) into media
Vining ~70 g (2.5 oz), side-dressed 2.8 g (½ tsp) in 1.5 gal water minimum
Flowering ~105 g (3.7 oz), side-dressed 4.2 g (¾ tsp) in 2 gal water minimum
Fruiting ~105 g (3.7 oz), side-dressed 5.6 g (1 tsp) in 2.5 gal water minimum, or split across irrigations

Container feeding: Liquid feed every 2–3 weeks; concentration is capped around 1.9–2.2 g per gallon to keep the drench safe in media where salts accumulate. Pair with Cal-Mag Plus at 5–10 ml per gallon depending on water hardness — coco and RO water need the higher end.

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 can serve as a nitrogen and calcium side-dress during fruiting on arid or sandy soils, but do not stack it on already high-EC media.

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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

Cucumber Fertilizer 8-16-36 vs other crop-specific Greenway formulas
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
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. Feed per plant: about 1.4 g at vining, 2.8 g at flowering, and 4.2 g at fruiting, adjusting water to hold your final measured EC in range. 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).

How do I feed cucumbers grown in containers or grow bags?

Container cucumbers feed in two phases. At potting, mix about ½ teaspoon of 8-16-36 per gallon of soil volume (roughly 2.8 grams per plant) thoroughly into the media. Then switch to a liquid feed of about ½ teaspoon per gallon of water — roughly 2.8 grams per plant — every 2 to 3 weeks, scaling down for seedlings and up as fruiting begins. Containers and coco media drain quickly and benefit from routine Cal-Mag Plus support for calcium and magnesium. The Guided Plan tab in the calculator above will build a full staged container schedule for your exact number of plants and pot size.

How often should I feed during fruiting?

Feeding frequency depends on your method. In hydroponic reservoirs, feed at the full fruiting rate (about 4.2 g per plant) and replace the solution every 7 to 14 days, monitoring EC between changes. In soil, side-dress at first fruit set and repeat every few weeks as fruiting continues. In containers, run a liquid feed every 2 to 3 weeks, stepping up to the fruiting rate. Across all methods, fruiting is when potassium demand peaks, so this is the stage to stay consistent — and to pair with a separate calcium source like Cal-Mag Plus for firm fruit.

Can I mix this with my Cal-Mag in the same tank?

No. Calcium and concentrated phosphate react to form insoluble calcium phosphate, which precipitates out as white cloudiness and makes both nutrients unavailable. Always pre-dissolve each product separately in warm water, then add them to the reservoir in order: calcium source first (pre-dissolved Calcium Nitrate if used), then Cal-Mag Plus stock, then the 8-16-36 solution last. Adjust pH after everything is fully dispersed. Never combine calcium sources and concentrated 8-16-36 in the same stock tank.

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.

What's the difference between this and your tomato fertilizer?

Both are high-potassium, water-soluble formulas built on the same chelated-micronutrient backbone, but the macronutrient ratios are tuned to different crops. Cucumber 8-16-36 runs a 4.5:1 K to N ratio with controlled nitrogen suited to trellised cucurbit vines. Tomato Fertilizer 4-18-38 runs a higher 9.5:1 ratio with even lower nitrogen, ideal once nightshades like tomatoes, peppers, and eggplant are flowering. If you're growing cucumbers, melons, squash, or other cucurbits, 8-16-36 is the right base. For fruiting nightshades, reach for the tomato formula instead.

Do I need to flush or hold back feeding before harvest?

Stop foliar feeding 7 days before harvest and rinse fruit before use. In soil, taper or skip the final scheduled side-dress as the last fruit ripens. In hydroponic systems, many growers run plain pH-adjusted water for the last week to finish clean. This is general best practice for flavor and shelf life, not a fix for a specific problem — a clean finish simply tends to produce better-tasting, longer-keeping fruit.

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.

12 / Documents

Lab-tested.
State-registered.

Every batch is traceable. Pull the SDS, the CDFA-approved label, and the most recent heavy metal analysis below.

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.

Choose your size →