4-18-38 with EDTA-chelated iron, manganese, zinc and copper, plus boron and molybdenum
Registration
CDFA-registered fertilizer
Sizes
1 Pound, 2 Pounds, 5 Pounds, 10 Pounds, 25 Pounds
Tomato Fertilizer 4-18-38
Price per lb by size: larger sizes save up to 66%
Size
Price
Per lb
Per lb vs 1 Pound
1 Pound
$ 24.99
$ 24.99
–
2 Pounds
$ 38.99
$ 19.50
22% less
5 Pounds
$ 59.99
$ 12.00
52% less
10 Pounds
$ 106.99
$ 10.70
57% less
25 Pounds
$ 214.99
$ 8.60
66% less
Shipping costs and limits
Continental US, Standard shipping: free on orders of $100 or more, $9.99 on orders under $50, and $14.99 from $50 up to $100.
UPS and FedEx options are also offered at checkout, at their own rates.
Orders placed by 11 AM Pacific on a business day ship the same day.
Alaska, Hawaii, US territories, APO/FPO and international addresses: the cost is shown at checkout, and 2-day delivery isn’t available to Alaska, Hawaii or P.O. boxes.
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
Guaranteed analysis and product specifications, Greenway Biotech Tomato Fertilizer 4-18-38
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.
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.
University potash (K₂O) recommendations for tomatoes, peppers, and eggplant, in pounds per acre, as soil-test potassium rises from low to medium, high, and very high
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
Weight of this 38% K₂O product that supplies a given potash recommendation, and the phosphate it brings
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:
The UF/IFAS hydroponic tomato recipe built on a 4-18-38 premix. Every stage keeps 16 lb of the premix in the A tank, giving 49 ppm phosphorus and 200 ppm potassium. Other amounts are per 30 gallons of stock at 1:100; results are ppm in the final solution, before any calcium or magnesium in your water
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.
The same recipe mixed as a fresh batch: grams per US gallon of final solution, with 2.42 g of this product per gallon at every stage
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.
What each bag size covers at the UF/IFAS solution rate and at a soil-test recommendation of 200 lb of potash per acre
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.
Tomato Fertilizer 4-18-38 compared with other Greenway water-soluble potash sources
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
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.
Related products & compatibility
These supply what Tomato Fertilizer 4-18-38 lacks. Use them in the same program, as your soil, water, or leaf test calls for; they are not all required.
Calcium Nitrate 15.5-0-0: nitrate nitrogen and calcium. It is the B-tank fertilizer in the UF/IFAS recipe above, and Clemson Extension’s tomato sidedress in the garden.
Epsom Salt (Magnesium Sulfate): magnesium and sulfur. UF/IFAS puts magnesium sulfate in the A tank with the 4-18-38, away from calcium nitrate.
Cal-Mag Plus 2-0-0 Concentrate: calcium and magnesium, with about 2% nitrate nitrogen. Follow the directions on its page, and keep it apart from this product until both are diluted.
Potassium Sulfate 0-0-53: potash without phosphate, for soil that already tests high in phosphorus.
Same program, separate concentrates. Dissolve this product and any calcium source separately. In concentrated form, calcium reacts with the phosphate in this product and settles out, which can clog emitters. Dilute each into the final solution, where they can be used together, and check the final solution for cloudiness, EC, and pH. In the garden, apply this product and a calcium nitrate sidedress as separate applications.
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.
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.
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.
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, 9 AM to 3 PM Pacific, and we will work through it with you.
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.
5 stars: 49 (80%)
4 stars: 6 (10%)
3 stars: 5 (8%)
2 stars: 0 (0%)
1 star: 1 (2%)
M
Maria Garcia
Fantastic products
We have been using your Tomato Fertilizer (along with others like the Lettuce and the Ammonium Calcium Nitrate) and we love them! Your products give our plants such vigor and great taste. The most important part is that your products are clean so we can rest easy.
C
Christo Pitarys
Contains no calcium
Contains no calcium, a micronutrient necessary to prevent blossom end rot.
Thanks for the feedback, Christo, and you're right, 4-18-38 has no calcium. That's intentional. Calcium and phosphate react and lock each other up when combined, so a high-phosphate fruiting formula has to leave calcium out to keep the phosphate available. The calcium goes in separately. Our Cal-Mag Plus 2-0-0 is built for that, applied on a separate watering day from the 4-18-38, and that pairing is what prevents blossom end rot. Reach us at questions@greenwaybiotech.com if you'd like help with rates.
J
Jack Acker
Great
Great product
K
Keith Foret
Looking good so
Looking good so far!
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Geri Reski
I don’t know yet..just applied
Too soon to tell how this affected growth and fruit production. I just received last week and applied.
M
Mike Aiello
Tomato fertilizer
I've used it before. That's why I'm using it again. It works!
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Frank Passalaqua
Great doing business with you.
It was a pleasure dealing with Greenway Biotech. Fast and easy when placing an order, and fast delivery. I'm sorry, however, as I can't comment on your tomato fertilizer as I just got it. I'll have to wait until I see the results your fertilizer has on my San Marzano tomatoes.
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William Harbour
So far
Only a short bit of the growing season to evaluate the performance of this tomato formulated fertilizer. Based on performance to this point, I will buy again.
J
John Wilson
Grow for succes
Using your product the past two seasons has improved my yields and quality of my tomatoes. My plants have thrived and production increased 135% my Cherokee Chocolate variety produced 59 lbs and Blackstar 74 lbs and still harvesting. I grow winter tomatoes in the Coachella valley and start picking in early January and done the middle of March. Irrigation Feed Fertilize Fungicide. It’s not rocket science but your product helps me look like one. Thank you
A
Anne Steele
Back yard gardener
I have used Greenway Biotech for several years and have been very pleased with the results. I like being able to get my nutrients in smaller quantities and the convenience of mail order.
J
Joseph Marley
Very easy to use. Seems to work well
Been using it three years now. I think it works well. Happy with how easy and fast it was to get the order
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Robert Thielges
First time fertilizer buy.
To early to tell on plant response yet. Just applied. Easy to use. If its anything like the other products I have purchased I expect great results.
J
Joe Williams
Thanks for your fast delivery
5 star I have used it last year
E
Ed Ronan
So far, so good
I really like that this is water soluble. I use tomato trays and using an empty 1gl. water bottle, add the fertilizer then pour into the trays. I just did my second feeding and think it is too early to give it 5 stars, but my plants are looking great! Many flowers and deep green foliage. So far, so good.
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Richard Schaefer
Too early to tell
Just applied the day I this request for a review.
Check back in a month
R
Richard Schaefer
Too early to tell
Just applied the day I this request for a review.
Check back in a month
M
Mike Aiello
Recent purchase
It’s only December. I’ll let you know. May 15th is when I plant the garden so in June get back to me. Thanks
J
Joshua Borchers
Works Great ...
Have used in Hydroponics. DUTCH BUCKETS for 8 years .. recently used in my aeroponic tower garden.. AMAZING GROWTH AND MANY MANY FLOWERS. HANGING ON TIGHT.....
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Stephen Cardwell
5 star
Worth every Penny nothing better
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Kat Tamborino
So Far, So Good!
My tomato plants seem to have been resuscitated by a couple of topical applications of this product. I should have used it earlier, but I have some new tomatoes and buds and the plants seem healthier. We'll see what else happens. Thanks!
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Misty Wright
Tomatoes For Days
In three days, I had many many more flowers on my tomatoe plants and now many tomatoes. This IS the secret after six years of growing and getting very little for all the work I did. It is now finally worth it. I’m going to have tons of tomatoes!!!
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cindy medeiros
tomato fertilizer
I love this product! Ive used it 2 times since I purchased it and have already seen a huge difference in the amt of tomatoes on my plants.It seemed some of my tomatoes had blossom drop (yes it was hot in central NC) but this 2nd 3rd and 4th round of flowers are producing fruit. Love that its water soluble.
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don nichols
Loads of tomatoes
I am using your product for the first time this year. I do believe it has improved the quality of my tomatoes tremendously. I would recommend this product.
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Terry Dougall
The secret to amazing tomatoes.
This is going to be a bumper crop of tomatoes, thanks to Greenway.
k
karl kriegel
tomatoe fertilizer
Great Product, Plants never looked better. Shipping was fast and came very well packaged!
K
Kevin Comeau
Small bags
I hope the produce turns out good price was high
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Michael Zampieri
Tomatoe results
Mixed your product accordingly. Next morning the tomatoes had grown 12 feet tall. Instead of tomatoes,the plants produced Bananas. This stuff is amazing.
T
Travis Outen
Great fertilizers
Nice easy to use no burn so far
D
Donald Hill
Absolutely Amazing!!!
I applied the 4-18-38 fertilizer for the first time about a week ago and starting to really see some results. I use it for everything in my garden and mix with RO water, Magnesium Sulfate(Epsom Salt), and Calcium Nitrate. The growth so far is off the charts and the plants all look healthy and vibrant. The plants also have beefed up a bit and are more sturdy. It does extremely well for tomatoes and peppers, but also squash, cucumbers, eggplant and the list goes on. I’m still pruning to get the size so I’m pulling what blooms form probably for another week and then I will let them fruit out. I’m going to keep using this product and continue to amend it with epsom salt and calcium nitrate and I recommend anyone else using this product do the same, because it doesn’t contain calcium or magnesium!
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Daniel Rivera
Tomato fertilizer 4-18-38
I think this product works very well. I highly recommend it to the public!
C
Carl Henley
Tomatoes
Prompt service and delivery of products. Will certainly use again. Anxiously waiting to see results from fertilizer. High expectations will post results when available.
My MSM is decreasing my osteoarthritis pain, especially in my hands
My product arrived intact. I started taking it as soon as I went into the kitchen. I mixed it with my daily Metamucil, but there was no discernible taste. I am working on making it a habit each morning. The pain from my osteoarthritis, especially in my hands, is decreasing. I expect it to continue to improve. Thank you for my MSM.
You did not send me MSM Powder, you sent me Magnesium Chloride powder. I tried contacting you 3 times, by email & phone and you didn't have the courage & honesty to return my messages & rectify the situation. I even offered to text you a photo of the mag chloride.
