Tomato Fertilizer 4-18-38 | Chelated Micronutrients | Hydroponics, Soil & Foliar Application
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Water-soluble fertilizer for tomatoes · 4-18-38 · chelated micronutrients · CDFA registered
About Tomato Fertilizer 4-18-38
Tomato Fertilizer 4-18-38 is a water-soluble fertilizer for tomatoes that supplies 38% soluble potash (K₂O), 18% available phosphate (P₂O₅), and 4% nitrogen, with EDTA-chelated iron, manganese, zinc, and copper plus boron and molybdenum. In a garden bed or field, size it by the potash your soil test recommends. In hydroponics, University of Florida IFAS builds a greenhouse tomato solution on a 4-18-38 premix, with magnesium sulfate in the premix tank and calcium nitrate in a separate tank; this product has the same nitrogen, phosphate, and potash analysis as that premix.
It is a potash and phosphate supplement, not a complete program. It contains no calcium or magnesium, and its 4% nitrogen covers only a small part of what a tomato crop needs. Keep its concentrate separate from calcium concentrates.
- 38% K₂O Each pound supplies 172 g of potash, 82 g of available phosphate, and 18 g of nitrogen
- 0.64 g per liter The UF/IFAS 4-18-38 rate in a hydroponic tomato solution, which this product turns into about 200 ppm potassium and 50 ppm phosphorus
- No Ca or Mg Supply calcium and magnesium separately. See companion products
Product facts & composition
| Specification | Detail |
|---|---|
| Total nitrogen (N) | 4.00% |
| Available phosphate (P₂O₅) | 18.00% |
| Soluble potash (K₂O) | 38.00% |
| Micronutrients | Iron, manganese, zinc, and copper, chelated with EDTA, plus boron and molybdenum. The guaranteed percentage of each is printed on the package label |
| Calcium, magnesium | None guaranteed |
| Form | White to off-white powder or fine granules. The Safety Data Sheet describes it as highly water-soluble and fully soluble at recommended use rates, and a 1% solution as acidic (about pH 4 to 6) |
| In solution | 1 g of product per liter adds 40 ppm nitrogen, 79 ppm phosphorus, and 315 ppm potassium. 1 g per US gallon adds 11 ppm N, 21 ppm P, and 83 ppm K |
| Registration | Registered with the California Department of Food and Agriculture (CDFA), as stated in Section 15 of the Safety Data Sheet |
| Heavy-metal test | An independent laboratory tested a sample received November 28, 2016 (reported December 7, 2016): arsenic, cadmium, cobalt, lead, mercury, nickel, and selenium were all below its detection limits. The detection limits for arsenic, cadmium, and lead (0.25, 0.03, and 0.5 mg/kg) are well below California’s limits for fertilizers. See Product documents |
| Hazards | Dust can irritate the eyes, skin, and airways. Harmful if swallowed in large amounts. Keep out of reach of children. See Handling, storage & limitations |
| Package sizes | 1, 2, 5, 10, and 25 lb |
Percentages are by weight. One pound supplies 172 g (0.38 lb) of potash (K₂O), 82 g (0.18 lb) of available phosphate (P₂O₅), and 18 g (0.04 lb) of nitrogen. Labels state phosphorus and potassium as oxides; the solution figures convert them to elements (P = P₂O₅ × 0.436, K = K₂O × 0.830), because hydroponic recipes use elemental ppm. Weigh the product: this page assumes no weight for a spoonful.
Best uses & benefits
Choose it when tomatoes need potash and phosphate together, and you have another source of nitrogen, calcium, and magnesium.
Tomatoes in beds and fields, on a soil test
The Mid-Atlantic Commercial Vegetable Production Recommendations call for 300, 200, 100, or 0 lb of potash per acre for fresh-market tomatoes as soil potassium tests low, medium, high, or very high, and set phosphate by the soil phosphorus test. This product supplies both: divide the potash your report recommends by 0.38. See the soil-test formula.
Drip-irrigated tomatoes on plastic mulch
The Mid-Atlantic recommendations split the potash for plastic-mulched tomatoes into two halves: one broadcast in the bed before laying the mulch, the other fed through the drip line during the season. Being water-soluble, this product can serve either half; keep its concentrate apart from any calcium source in the injector.
Hydroponic and greenhouse tomatoes
University of Florida IFAS doses a 4-18-38 premix at 16 lb per 30-gallon stock tank, injected at 1:100, beside a separate calcium nitrate stock that rises with each growth stage. At that rate this product supplies about 200 ppm potassium and 50 ppm phosphorus. See the hydroponic recipe.
Where it is a poor fit
- Soils already high in phosphorus. Every pound of potash from this product brings 0.47 lb of phosphate. For potash alone, Potassium Sulfate 0-0-53 adds none.
- Soils that test very high in potassium. The Mid-Atlantic recommendations call for no potash on tomato soils testing very high, and University of Florida IFAS none on soils testing high.
- The main nitrogen source. At the Mid-Atlantic medium-potassium rate it brings about 21 lb of nitrogen per acre, against the 80 to 90 lb the same recommendations give fresh-market tomatoes on bare ground and 120 to 200 lb on plastic mulch with drip.
- Calcium or magnesium. It contains neither. Use Calcium Nitrate, Gypsum, Cal-Mag Plus, or Epsom Salt as your soil or water test calls for.
- Crops not on the label, and forage. It contains boron, which can injure crops the label does not list, and molybdenum, which can build up in forage to levels toxic to cattle, sheep, and goats.
- Containers and foliar sprays. This page gives no rate for either; see Application rates.
Application rates & directions
Use one of two bases: a soil test’s potash recommendation for a bed or field, or a recipe for a nutrient solution. Weigh the product. If the directions printed on your package differ from this page, contact us before applying.
Test first. A soil test is the guide to how much potash and phosphate a planting needs; the University of Minnesota advises applying phosphorus and potassium according to a soil test. University guides put tomato soil pH at 6.0 to 6.5 (Clemson) or 6.2 to 6.8 (University of Georgia). For nutrient solutions, test your water for potassium, calcium, and magnesium before you mix.
Beds and fields: size it by a soil test
Formula. Pounds of product = pounds of potash (K₂O) your soil test recommends ÷ 0.38. Multiply by 453.6 for grams. Broadcast it and work it in before planting. On plastic mulch, the Mid-Atlantic recommendations broadcast half the potash in the bed and feed the other half through the drip line.
| Source and crop | Low / medium / high / very high |
|---|---|
| Mid-Atlantic, fresh-market tomatoes | 300 / 200 / 100 / 0 |
| Mid-Atlantic, processing tomatoes | 250 / 150 / 100 / 0 |
| UF/IFAS, Florida tomatoes (three levels) | 125–150 / 100 / 0 |
| Mid-Atlantic, peppers | 200 / 150 / 100 / 0 |
| Mid-Atlantic, eggplant | 250 / 150 / 100 / 0 |
| K₂O recommended per acre | This product | Phosphate (P₂O₅) it brings |
|---|---|---|
| 50 lb | 132 lb per acre; 137 g (0.30 lb) per 100 sq ft | 24 lb per acre |
| 100 lb | 263 lb per acre; 274 g (0.60 lb) per 100 sq ft | 47 lb per acre |
| 150 lb | 395 lb per acre; 411 g (0.91 lb) per 100 sq ft | 71 lb per acre |
| 200 lb | 526 lb per acre; 548 g (1.21 lb) per 100 sq ft | 95 lb per acre |
| 300 lb | 789 lb per acre; 822 g (1.81 lb) per 100 sq ft | 142 lb per acre |
Mid-Atlantic figures are from the Tomatoes, Peppers, and Eggplant chapters of the 2026/2027 Mid-Atlantic Commercial Vegetable Production Recommendations, which say a state soil-test report or nutrient management plan takes precedence over its table. University of Florida IFAS figures are from its Vegetable Production Handbook fertilizer chapter (CV296), for fertigated crops on Florida mineral soils, on three Mehlich-3 levels: low 35 ppm potassium or less, medium 36 to 60, high above 60. The Mid-Atlantic fresh-market figures apply on bare ground and as the total on plastic mulch. In California, the CDFA and UC Davis processing-tomato guidelines treat an ammonium-acetate soil test of 135 ppm potassium as adequate for furrow irrigation and 200 ppm for drip, and add potassium only when the test shows it is short. Soil-test labs define low, medium, and high differently, so use the recommendation printed on your own report. Each pound of potash from this product also brings 0.47 lb of phosphate and 0.11 lb of nitrogen; if your report calls for potash but little or no phosphate, use a potash-only source instead.
Nitrogen and calcium come from other fertilizers
The Mid-Atlantic recommendations give fresh-market tomatoes on bare ground 80 to 90 lb of nitrogen per acre, half broadcast before planting and half sidedressed when the first fruits are set, and 120 to 200 lb on plastic mulch with drip; University of Florida IFAS gives 200 lb for Florida tomatoes. In the garden, the University of Minnesota sidedresses nitrogen when the first fruits start to enlarge, and the University of Georgia sidedresses a complete fertilizer when the first fruit is about the size of a quarter, then every 3 to 4 weeks. Clemson Extension sidedresses calcium nitrate at 1 lb per 100 sq ft (about 30 feet of row) 3 to 4 weeks after planting; on sandy soil it may need to be split into two applications 3 to 4 weeks apart. Too much nitrogen is a problem too: the University of Minnesota says it gives bushy, leafy plants that are slow to bear fruit. For calcium in soil, lime to the pH your soil test calls for; where pH is already on target but calcium is low, the University of Georgia uses gypsum at 1 lb per 100 sq ft.
Hydroponic and greenhouse solutions: the UF/IFAS 4-18-38 recipe
University of Florida IFAS (HS796/CV216, revised December 2024) formulates a Florida greenhouse tomato solution on a 4-18-38 premix. Its A stock tank holds 16 lb of the premix and 10 to 12 lb of magnesium sulfate; a separate B stock tank holds calcium nitrate, which rises with each growth stage. Both tanks are 30 gallons, injected at 1:100. That is 0.64 g of 4-18-38 per liter of final solution, and at that rate this product supplies the same nitrogen, phosphorus, and potassium as the UF/IFAS premix:
| Stage | Stock tanks | Final ppm |
|---|---|---|
| 1: transplant to first cluster | A: 10 lb magnesium sulfate. B: 7.5 lb calcium nitrate | N 70, Ca 56, Mg 40 |
| 2: first to second cluster | A: 10 lb magnesium sulfate. B: 9.5 lb calcium nitrate | N 82, Ca 71, Mg 40 |
| 3: second to third cluster | A: 10 lb magnesium sulfate. B: 12.0 lb calcium nitrate | N 100, Ca 94, Mg 40 |
| 4: third to fifth cluster | A: 12 lb magnesium sulfate. B: 16.5 lb calcium nitrate | N 124, Ca 124, Mg 48 |
| 5: fifth cluster to end of crop | A: 12 lb magnesium sulfate. B: 20.5 lb calcium nitrate | N 148, Ca 154, Mg 48 |
UF/IFAS’s stage targets (its Table 1) call for 150 ppm calcium at every stage. The recipe relies on Florida well water, which UF/IFAS says may carry 40 to 60 ppm calcium, some but probably not all of it available to the crop, so test your water and count its calcium. If two 1:100 injectors run in parallel on one water line, UF/IFAS doubles the stock-tank amounts.
| Stage | Calcium nitrate, dissolved separately | Magnesium sulfate |
|---|---|---|
| 1 | 1.13 g | 1.51 g |
| 2 | 1.44 g | 1.51 g |
| 3 | 1.81 g | 1.51 g |
| 4 | 2.49 g | 1.81 g |
| 5 | 3.10 g | 1.81 g |
Multiply by the gallons in your batch; the calculator below does the arithmetic. UF/IFAS sets the final solution at pH 5.8 to 6.2.
Potassium and blossom-end rot. The same UF/IFAS publication targets less potassium in the early stages (120 ppm in stages 1 and 2, 150 in stages 3 and 4, 200 in stage 5) and warns that premixes deliver large amounts of potassium. With water below 50 ppm calcium, excess potassium from the A stock can bring early blossom-end rot, because potassium interferes with calcium uptake by the root, and UF/IFAS calls lower potassium the better fix. To dose to a lower potassium target, use grams of product = (potassium target − potassium in your water, in ppm) × liters of final solution ÷ 315.4; at 120 ppm this product supplies about 30 ppm phosphorus, below the recipe’s 50.
Micronutrients. The UF/IFAS premix carries its own micronutrient analysis, which may differ from this product’s, so the micronutrient figures in that publication do not transfer. Compare the guarantees on your package label with your recipe’s targets, and add a micronutrient only if a water or tissue test calls for it.
EC and pH. UF/IFAS gives no EC target. Ohio State University puts tomato solution EC at about 2.0 dS/m early in the crop, rising toward 2.4 later; Oklahoma State’s hydroponics table lists 2.0 to 4.0 mS/cm at pH 6.0 to 6.5 and advises checking pH and EC daily and replacing the solution every two weeks. Start at the low end and measure your own solution.
Separate stocks. Penn State Extension keeps calcium in a different stock tank from phosphates and sulfates, because they form precipitates that can clog drip emitters, and Ohio State names the precipitates as gypsum and rock phosphate. UMass Extension injects its two greenhouse tomato stocks at the same time, at 1:100 each, so they mix only after dilution.
Containers and foliar sprays
This page gives no container or foliar rate. University container guides (University of Maryland; Texas A&M) feed container tomatoes regularly with a water-soluble fertilizer by its label and water until it drains from the bottom so salts do not build up. University of Florida IFAS finds foliar calcium unlikely to correct deficiencies, and the CDFA and UC Davis guidelines report no effect from foliar potassium on soil already high in potassium. Email questions@greenwaybiotech.com with your container size and growing mix, or your crop and sprayer volume, before using it either way.
How to use Tomato Fertilizer 4-18-38
- Test and plan. Get a soil test for beds and fields, or a water test for nutrient solutions. Adjust soil pH if the test calls for it, and plan nitrogen and calcium from other fertilizers.
- Pick one basis and weigh the dose. Divide your soil test’s potash recommendation by 0.38 for a bed or field, or follow your nutrient solution recipe. The calculator below does the arithmetic.
- Apply it. Beds and fields: broadcast it evenly and work it in before planting, or on plastic mulch split it between the bed and the drip line. Solutions: dissolve it on its own and keep its concentrate in a different stock tank from calcium nitrate or Cal-Mag.
- Add nitrogen and keep watering even. Sidedress nitrogen when the first fruits set, from another fertilizer. Water deeply and evenly and mulch the soil: university guides name uneven moisture as a common cause of blossom-end rot.
- Repeat only as the basis says. Soil-test amounts: once per season, then retest. Solutions: Oklahoma State Extension advises checking pH and EC daily and replacing the solution every two weeks.
Calculator & choosing a size
Formulas. Beds and fields: pounds of product = pounds of potash (K₂O) recommended for the area ÷ 0.38. UF/IFAS recipe: 0.64 g of product per liter of final solution (16 lb per 30-gallon stock at 1:100). Your own potassium target: grams of product = (target − potassium in your water, in ppm) × liters of final solution ÷ 315.4. Multiply pounds by 453.6 for grams, and US gallons by 3.785 for liters.
Worked examples. A 200 sq ft bed whose soil test recommends 3 lb of potash per 1,000 sq ft: 0.2 × 3 = 0.6 lb of K₂O, ÷ 0.38 = 1.58 lb (716 g) of product, supplying 129 g of phosphate and 29 g of nitrogen; a 2 lb bag covers it. A 50-gallon fresh batch at the UF/IFAS stage 3 recipe: 0.64 g × 189.3 L = 121 g of product; a 1 lb bag covers it, and the separate calcium nitrate is 91 g and the magnesium sulfate 76 g. A 30-gallon stock tank at 1:100: 16 lb (7,257 g) of product, as in the UF/IFAS recipe; a 25 lb bag covers it, and the calculator also shows any lower-price combination of smaller bags. A 50-gallon batch dosed to 150 ppm potassium from water with 5 ppm: 145 × 189.3 ÷ 315.4 = 87 g.
| Bag size | Final solution at 0.64 g per liter | Area at 200 lb K₂O per acre |
|---|---|---|
| 1 lb (454 g) | About 188 gallons | About 83 sq ft |
| 2 lb (907 g) | About 375 gallons | About 166 sq ft |
| 5 lb (2.27 kg) | About 938 gallons | About 414 sq ft |
| 10 lb (4.54 kg) | About 1,875 gallons | About 828 sq ft |
| 25 lb (11.3 kg) | About 4,688 gallons | About 2,069 sq ft |
The calculator below asks how large your bed or field is and what potash your soil test recommends, or the volume of your batch or stock tank and which recipe you follow. It applies your test result, the UF/IFAS recipe, or your own potassium target, states the nutrients supplied, and recommends the smallest single bag that covers one application or batch (or the lowest-price set of bags when no single bag does), plus a lower-price bag combination when one exists. Prices, tax, and shipping are confirmed at checkout, and availability is confirmed when you add to cart.
The calculator needs JavaScript. If it does not appear, use the tables and formulas above to choose a size.
How Tomato Fertilizer 4-18-38 works
Potassium is the nutrient this product supplies most of: 9.5 parts potash to 1 of nitrogen. University of Minnesota Extension explains that potassium helps regulate the opening and closing of leaf stomata, which controls water loss and gas exchange, maintains turgor, and enhances the movement of sugars and starch in the plant. In tomatoes, the CDFA and UC Davis guidelines link a potassium shortage to the ripening disorders yellow shoulder and blotchy ripening, and the Mid-Atlantic recommendations aim for leaf potassium of at least 3% before the fruit is an inch across, noting that high nitrogen or low potassium increases blotchy ripening. More is not better: the same California guidelines note that excess potassium can reduce calcium and magnesium uptake.
Its low nitrogen is deliberate. Nitrogen grows leaves, and the University of Minnesota warns that too much makes tomato plants slow to bear fruit, so nitrogen is planned separately, usually as a sidedress when fruit sets or, in hydroponics, as calcium nitrate in its own stock tank.
Blossom-end rot is a calcium problem inside the fruit, not usually a shortage in the soil. The Mid-Atlantic recommendations describe it as inadequate movement of calcium into the fruit, made worse by low soil moisture; University of Wisconsin and UMass Extension add that high ammonium, potassium, or magnesium compete with calcium for uptake. University sources disagree on calcium sprays: University of Florida IFAS reports that foliar calcium has not been shown to reduce it, while UMass Extension gives calcium chloride spray directions. Even watering, mulch, liming to the soil test, and a balanced potassium supply are what university guides rely on. This product contains no calcium, and its phosphate reacts with calcium in concentrated form to make insoluble calcium phosphate, which is why nutrient recipes keep calcium nitrate in its own stock tank; once each is diluted into the final solution they can be used together. This describes plant nutrition in general; it is not a trial of this finished product.
Compare your options
Match the product to your crop and your soil or water test. Analyses are each product’s guarantee as shown on its page.
| Option | N–P₂O₅–K₂O | Potash per part nitrogen | Choose it when |
|---|---|---|---|
| Tomato Fertilizer 4-18-38, this product | 4-18-38, chelated micronutrients | 9.5 | You grow tomatoes and need potash and phosphate with little nitrogen |
| Pepper & Herb Fertilizer 11-11-40 | 11-11-40 | 3.6 | You grow peppers or the culinary herbs on its label |
| Cucumber Fertilizer 8-16-36 | 8-16-36 | 4.5 | You grow cucumbers, squash, and melons |
| Lettuce Fertilizer 8-15-36 | 8-15-36 | 4.5 | You grow lettuce and the leafy greens on its label |
| Strawberry Fertilizer 8-12-32 | 8-12-32 | 4.0 | You grow strawberries |
| Potassium Sulfate 0-0-53 | 0-0-53, 17% sulfur | No nitrogen | You need potash only, on soil already high in phosphorus |
| Monopotassium Phosphate 0-52-34 | 0-52-34 | No nitrogen | You build a solution from single salts and need phosphorus and potassium without nitrogen |
None of these contains calcium or magnesium. Each crop formula contains boron, so follow each product’s label for the crops it names.
Handling, storage & limitations
- Hazards. Keep out of reach of children. Dust may irritate the eyes, skin, and airways, and the product is harmful if swallowed in large amounts. Avoid raising dust and avoid contact with the eyes.
- Protective equipment. The Safety Data Sheet recommends nitrile gloves and safety glasses with side shields, goggles when mixing concentrated solutions, and a NIOSH-approved N95 or P100 respirator when handling large amounts in an enclosed space. Do not eat, drink, or smoke while handling it, and wash your hands afterward.
- Crop limits. It contains boron, and use on crops not listed on the label may cause serious crop injury. It contains molybdenum, and use on forage or pasture can raise molybdenum to levels toxic to ruminant animals such as cattle, sheep, and goats. Use it only on the crops the label names, and not on forage or pasture.
- Storage. Keep it in the original container, tightly sealed, in a cool, dry, well-ventilated place; the Safety Data Sheet recommends 40 to 95°F. It absorbs moisture from the air; caking does not change it chemically. Store it away from heat, open flames, and combustible materials, away from food, feed, and drinking water, and out of reach of children. Do not mix the dry product with calcium fertilizers.
- Spills and disposal. Sweep or vacuum spills without raising dust, and keep the product out of drains and waterways, where phosphate feeds algae. Use leftover product as fertilizer following the label. Triple-rinse empty containers, use the rinse water as dilute fertilizer, and dispose of the containers as local rules require.
- Use limits. Weigh every application, and follow one basis at a time: a soil test or a solution recipe. It is not a complete fertilizer and contains no calcium or magnesium.
- First aid. Eyes: flush with clean running water for at least 15 minutes and remove contact lenses if easy to do; get medical attention if irritation persists. Skin: brush off dry material and wash with soap and water; get medical attention if irritation persists. Inhaled: move to fresh air; get medical attention if symptoms persist. Swallowed: do not induce vomiting; rinse the mouth, give one to two glasses of water if the person is conscious and alert, and contact Poison Control or a doctor.
- Emergency numbers from the Safety Data Sheet. CHEMTREC 1-800-424-9300 (US, 24 hours) or +1-703-527-3887 (international); Poison Control 1-800-222-1222.
Frequently asked questions
What does Tomato Fertilizer 4-18-38 contain?
It guarantees 4% nitrogen, 18% available phosphate (P₂O₅), and 38% soluble potash (K₂O), with iron, manganese, zinc, and copper chelated with EDTA, plus boron and molybdenum; the percentage of each micronutrient is printed on the package label. It contains no calcium or magnesium. Each pound supplies 172 g of potash, 82 g of phosphate, and 18 g of nitrogen.
How much should I use on a garden bed or field?
Size it by a soil test: pounds of product equal the pounds of potash (K₂O) your test recommends, divided by 0.38, broadcast and worked in before planting. For example, 3 lb of potash per 1,000 sq ft on a 200 sq ft bed is 1.58 lb (716 g) of product. The Mid-Atlantic recommendations call for 300 lb of potash per acre for fresh-market tomatoes on low-potassium soil, 200 on medium, 100 on high, and none on very high. Use the figure on your own report, and if it calls for little or no phosphate, use a potash-only source instead.
How do I use it in a hydroponic system?
University of Florida IFAS builds a greenhouse tomato solution on a 4-18-38 premix: 16 lb of premix and 10 to 12 lb of magnesium sulfate in a 30-gallon A stock tank, and 7.5 to 20.5 lb of calcium nitrate, rising by growth stage, in a separate 30-gallon B tank, each injected at 1:100. That is 0.64 g of this product per liter of final solution, supplying about 200 ppm potassium, 50 ppm phosphorus, and 26 ppm nitrogen. UF/IFAS targets less potassium early in the crop and warns that excess potassium with water below 50 ppm calcium can bring early blossom-end rot; to dose to a lower target, use grams = (target ppm K minus the K in your water) × liters ÷ 315.4. Keep the final solution at pH 5.8 to 6.2.
Do I need calcium nitrate with it?
In a nutrient solution, yes, or another calcium source: this product contains no calcium, and the UF/IFAS recipe puts calcium nitrate in its own stock tank at 7.5 to 20.5 lb per 30 gallons by growth stage. In soil, calcium usually comes from liming to the pH your soil test calls for, or from gypsum where pH is on target but calcium is low. Calcium nitrate is also a common tomato sidedress for nitrogen; Clemson Extension uses 1 lb per 100 sq ft 3 to 4 weeks after planting.
Can I mix it with calcium nitrate or Cal-Mag?
Not as concentrates. Calcium reacts with the phosphate in this product to form insoluble calcium phosphate, which settles out and can clog emitters. Dissolve each product separately, keep them in different stock tanks, and dilute each into the final solution, where they can be used together. Then check the final solution for cloudiness, EC, and pH. In the garden, apply them as separate feedings.
Will it prevent blossom-end rot?
No fertilizer can promise that. Blossom-end rot is too little calcium reaching the developing fruit, usually because of uneven soil moisture rather than a calcium shortage in the soil. University guides rely on deep, even watering, mulch, liming to the soil test, and avoiding excess nitrogen; University of Wisconsin and UMass Extension note that high ammonium, potassium, or magnesium compete with calcium for uptake. This product contains no calcium, and in hydroponics UF/IFAS warns that excess potassium with low-calcium water can bring early blossom-end rot, so dose potassium to your recipe and supply calcium separately. University sources disagree on calcium sprays: University of Florida IFAS reports that foliar calcium has not been shown to reduce it, while UMass Extension gives calcium chloride spray directions.
Do I still need a nitrogen fertilizer?
Yes. The Mid-Atlantic recommendations give fresh-market tomatoes on bare ground 80 to 90 lb of nitrogen per acre, half before planting and half when the first fruits are set, and 120 to 200 lb on plastic mulch with drip; University of Florida IFAS gives 200 lb. At the Mid-Atlantic medium-potassium rate this product brings about 21 lb. In the garden, the University of Minnesota sidedresses nitrogen when the first fruits start to enlarge, and warns that too much makes plants bushy, leafy, and slow to bear fruit.
What EC and pH should a hydroponic tomato solution have?
University sources differ. UF/IFAS sets the pH at 5.8 to 6.2 and gives no EC target. Ohio State University puts EC at about 2.0 dS/m early in the crop, rising toward 2.4 later, and Oklahoma State lists 2.0 to 4.0 mS/cm at pH 6.0 to 6.5, with pH and EC checked daily and the solution replaced every two weeks. Start at the low end and measure your own solution.
Can I use it on peppers and eggplant?
Only if your package label lists them: the product contains boron, and the label warns that use on crops it does not name can cause serious injury. Where the label lists them, size it by a soil test as for tomatoes. The Mid-Atlantic recommendations call for 200, 150, 100, or 0 lb of potash per acre for peppers and 250, 150, 100, or 0 lb for eggplant as soil potassium tests low to very high. Do not use it on forage or pasture.
Can I use it in containers or as a foliar spray?
This page gives no rate for either. University container guides feed container tomatoes regularly with a water-soluble fertilizer by its label and water until it drains so salts do not build up. University of Florida IFAS finds foliar calcium unlikely to correct deficiencies, and the CDFA and UC Davis guidelines report no effect from foliar potassium on soil already high in potassium. Email questions@greenwaybiotech.com with your container size and mix, or your crop and sprayer volume, before using it either way.
Related guides & articles
- Calcium in Plants: Function, Deficiency & Fertilizers: why calcium moves with water, why blossom-end rot is a delivery problem, and why calcium and phosphate concentrates are kept apart.
- What Is the Best Calcium Fertilizer?: how to choose between calcium nitrate, gypsum, lime, and Cal-Mag for your soil or solution.
- What Does Potassium Do for Plants?: how potassium works in the plant, what a shortage looks like, and the main potash sources.
Articles give background. For this product, use the rates and documents on this page.
Product documents & sources
- Product label (PDF): the CDFA-approved label for this product (file dated July 3, 2017).
- Safety Data Sheet (PDF): handling, storage, first aid, and emergency numbers. Version 1.0, issued April 2026.
- Heavy-metal analysis (PDF): an independent laboratory test of one sample of this product, received November 28, 2016 and reported December 7, 2016. Arsenic, cadmium, cobalt, lead, mercury, nickel, and selenium were below the laboratory’s detection limits.
Where the rates and statements on this page come from
The analysis, crop limits, and cautions come from the product label and Safety Data Sheet, the safety statements from the Safety Data Sheet, the heavy-metal limits from the California regulation listed last, and the soil-test, nitrogen, hydroponic, blossom-end rot, and plant-nutrition statements from the university, agency, and regulatory publications below, which explain crop nutrition but do not evaluate or endorse this product.
- Mid-Atlantic Commercial Vegetable Production Recommendations 2026/2027, Tomatoes (Rutgers NJAES copy): potash and phosphate by soil test, nitrogen and its timing, the plastic-mulch split, leaf potassium and blotchy ripening, and blossom-end rot.
- Mid-Atlantic recommendations, Peppers and Eggplant: potash by soil test for each crop.
- University of Florida IFAS, Fertilizer Management for Vegetable Production in Florida (CV296): Florida tomato potash by Mehlich-3 soil test, nitrogen, and foliar calcium.
- CDFA Fertilizer Research and Education Program with UC Davis, California Fertilization Guidelines: Processing Tomato: soil-test potassium thresholds, ripening disorders, excess potassium, and foliar potassium.
- University of Minnesota Extension, Growing Tomatoes in Home Gardens: phosphorus and potassium by soil test, sidedress timing, and excess nitrogen.
- University of Georgia Extension, Georgia Homegrown Tomatoes (B1271): soil pH, sidedress timing, and gypsum where calcium is low.
- Clemson Cooperative Extension, Tomato (HGIC 1323): soil pH and the calcium nitrate sidedress.
- University of Florida IFAS, Nutrient Solution Formulation for Hydroponic (Perlite, Rockwool, NFT) Tomatoes in Florida (HS796/CV216, rev. 2024): the 4-18-38 premix recipe, stage targets, solution pH, and the potassium and blossom-end rot caution.
- Ohio State University, Hydroponic Nutrient Solution for Optimized Greenhouse Tomato Production (HYG-1437): solution EC by stage and the precipitates formed in concentrate.
- Oklahoma State University Extension, Electrical Conductivity and pH Guide for Hydroponics (HLA-6722): the tomato EC and pH range and solution monitoring.
- Penn State Extension, Hydroponics Systems: Using the Two Basic Equations to Calculate a Nutrient Solution Recipe: keeping calcium in a different stock tank from phosphates and sulfates.
- UMass Extension, Greenhouse Tomatoes: Fertilizing Plants Growing in Soilless Media: two stock tanks injected at the same time.
- University of Wisconsin, Blossom End Rot (D0022) and UMass Extension, Solanaceous Blossom End Rot: causes of blossom-end rot and the nutrients that compete with calcium.
- University of Florida IFAS, Physiological, Nutritional, and Other Disorders of Tomato Fruit (HS-954): blossom-end rot and foliar calcium.
- University of Minnesota Extension, Potassium for Crop Production: the roles of potassium in the plant.
- University of Maryland Extension, Maintaining Container Grown Vegetables and Texas A&M AgriLife Extension, Vegetable Gardening in Containers (E-545): feeding container vegetables and flushing salts.
- California Code of Regulations, Title 3, § 2302, Non-Nutritive Standards: California’s arsenic, cadmium, and lead limits for fertilizers.
Rates and sources reviewed October 17, 2026.
Help choosing & next step
Not sure how to read your soil test, how to fit this product into a nutrient recipe, or which calcium source suits your water? Email your crop, growing method, and soil or water test results to questions@greenwaybiotech.com, or call (562) 351-5168, Monday to Friday, 7 AM to 5 PM Pacific, and we will work through it with you.
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Every order carries a 90-day satisfaction guarantee, and we pack and ship from Madera, California. You can also choose a package weight from the size selector at the top of this page.
Greenway Biotech, Inc. is a family-owned company that has blended and packaged specialty fertilizers and soil amendments in California since 1989, today from Madera.
