Feeding Programs / Tomatoes
Tomato Feeding Program: A Stage-by-Stage Schedule for Beds, Containers and Hydroponics
Choosing a tomato fertilizer is half the job. The other half is timing: what goes into the soil before planting, when the first sidedress is due, how a nutrient solution gets stronger as each flower cluster opens, and how far into the harvest to keep going. This program lays that out for garden beds, containers and hydroponics, built around the three parts of the Greenway Complete Tomato Feeding Kit.
The short answer: in garden beds, work Tomato Fertilizer 4-18-38 in before planting at the amount your soil test sets, then sidedress Calcium Nitrate 15.5-0-0 starting three to four weeks after planting. In containers and hydroponics, weigh all three kit parts into a fresh solution, and step up the Calcium Nitrate (and later the Epsom Salt) each time the plants reach a new flower cluster. In every system, steady watering matters as much as the fertilizer.
See the program at a glance Which fertilizer, and why
- 3 parts Tomato Fertilizer 4-18-38, Calcium Nitrate 15.5-0-0 and Epsom Salt for Plants, in separate bags
- 5 stages Solution strength steps up by flower cluster, from transplant to the end of the crop
- 3–4 wk After planting: the first Calcium Nitrate sidedress in garden beds (Clemson Extension)
The Program
One kit, three ways to use it.
The kit holds the three Greenway fertilizers a hydroponic or container tomato crop needs, sized to run out at about the same time. In garden beds, the same three products are used separately, on a soil test.
| Size | Tomato Fertilizer 4-18-38 | Calcium Nitrate 15.5-0-0 | Epsom Salt for Plants | Makes about |
|---|---|---|---|---|
| Starter | 2 lb | 2 lb | 1 lb | 250 to 300 gallons |
| Season | 5 lb | 5 lb | 3 lb | 730 to 900 gallons |
Gallons are for the kit's Standard recipe: the lower figure is at full late-season strength (stage 5), the higher one at stages 1 to 3. Each part does a different job. Tomato Fertilizer 4-18-38 supplies phosphorus, potassium and EDTA-chelated micronutrients, but no calcium or magnesium and only a little nitrogen. Calcium Nitrate 15.5-0-0 supplies calcium and most of the nitrogen. Epsom Salt for Plants supplies magnesium and sulfur. They stay in separate bags because concentrated calcium reacts with phosphate and sulfate and settles out; once each is diluted, they work together.
Three systems, three ways to set the schedule
| System | What sets the amount | What sets the timing | Kit parts used |
|---|---|---|---|
| Garden beds and in-ground rows | Your soil test (Tomato Fertilizer) and Clemson Extension's sidedress rates (Calcium Nitrate) | Weeks after planting | Tomato Fertilizer before planting; Calcium Nitrate as a sidedress; Epsom Salt only if magnesium tests low |
| Containers | The kit's feeding chart, in grams per gallon, matched to your water | The plant's flower clusters | All three, weighed into a solution |
| Hydroponics | The kit's feeding chart, matched to your water | The plant's flower clusters | All three, in one batch or two injector stock tanks |
Which fertilizer, and why?
This article covers when and how much. For why tomatoes want a low-nitrogen, high-potash formula once they flower, and how 4-18-38 compares with other options, see What is the Best Fertilizer for Tomatoes?
The Schedule
The whole season, at a glance.
Beds run on the calendar, counted from planting day. Containers and hydroponics run on the plant: move to the next stage when the plants reach the next flower cluster, not by the calendar.
| System | Before planting | During the season | Through the last harvest |
|---|---|---|---|
| Garden beds | Soil test; lime if the test calls for it; Tomato Fertilizer broadcast and worked in at the soil-test amount | Calcium Nitrate sidedress from 3–4 weeks after planting, on one of two Clemson programs | Deep, even watering and mulch; no extra nitrogen beyond the program |
| Containers | Water test; choose the Standard or Soft water recipe; a pot of 4 gallons or more for standard varieties | Kit solution at the strength for the current stage, watered through until it drains | Stage 5 strength from the fifth cluster to the end of the crop |
| Hydroponics | Water test; choose the Standard or Soft water recipe | Stages 1 to 4: Calcium Nitrate rises at each new cluster, Epsom Salt rises at stage 4 | Stage 5 strength to the end of the crop; pH and EC checked daily, solution replaced every two weeks |
The five solution stages
| Stage | Starts | Ends | What changes in the Standard recipe |
|---|---|---|---|
| 1 | Transplant | First flower cluster | Starting strength |
| 2 | First cluster | Second cluster | More Calcium Nitrate |
| 3 | Second cluster | Third cluster | More Calcium Nitrate |
| 4 | Third cluster | Fifth cluster | More Calcium Nitrate and more Epsom Salt |
| 5 | Fifth cluster | End of the crop | Full late-season strength |
Tomato Fertilizer stays at 2.42 g per gallon at every stage of the Standard recipe; the nitrogen and calcium rise with the Calcium Nitrate. That follows the University of Florida IFAS stage targets, which raise nitrogen from 70 ppm at transplant to 150 ppm in the last stage[1]. The exact grams for each stage are in the hydroponics section.
Before Transplant
Before planting: test the soil or the water.
Every amount in this program depends on one thing you measure first: the potash your soil test recommends for a bed, or the calcium in your water for a solution.
Garden beds: start with a soil test
Clemson Extension calls a soil test "always the best method of determining the fertilization needs of the crop," and applies lime and pre-plant fertilizer according to it[2]. University guides put tomato soil pH at 6.0 to 6.5 (Clemson)[2] or 6.2 to 6.8 (University of Georgia)[4]. If your test calls for lime, Clemson applies limestone 3 to 6 months ahead and tills it in[3].
Tomato Fertilizer 4-18-38 then goes in once, before planting. The rate comes from the Tomato Fertilizer page: 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; Clemson incorporates pre-plant fertilizer to a depth of around 6 inches[2]. Use it once per season, then retest.
| K₂O recommended per acre | Tomato Fertilizer 4-18-38 | 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 |
Worked example (from the product page): 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. If your report calls for potash but little or no phosphate, use a potash-only source such as Potassium Sulfate 0-0-53 instead. Use the figure printed on your own report; labs define low, medium and high differently.
Containers and hydroponics: test the water
The kit chart has two recipes, and the calcium in your water decides which one to use. Test your water once, or ask your water utility for its report, for calcium, magnesium, potassium, pH and alkalinity (bicarbonate).
| Your water | Use |
|---|---|
| Calcium 50 ppm or more (most well water, hard tap water) | Standard: the UF/IFAS formula as published, which counts on 40 to 60 ppm calcium from the water |
| Calcium under 50 ppm (reverse osmosis, rain, soft tap water) | Soft water: less Tomato Fertilizer in stages 1 to 4 and a little more Calcium Nitrate in stages 1 to 3 |
The reason for the second recipe is potassium. UF/IFAS warns that excess potassium from the fertilizer, combined with well water below 50 ppm calcium, can bring an early problem with blossom end rot, because potassium interferes with calcium uptake by the root[1].
Still at the seedling stage?
The kit chart starts at transplant and gives no rate for seedlings in trays, so follow the label for those. For light, potting up and hardening off, see How to Care for the Seedlings in Your Garden.
Garden Beds
Garden beds, week by week.
In soil, Tomato Fertilizer goes in once, before planting, and Calcium Nitrate carries the season as a sidedress. The kit's per-gallon chart is for nutrient solutions, not beds.
| When | What to do | Product and amount |
|---|---|---|
| 3 to 6 months before planting | Lime and till it in, only if your soil test calls for it | As your soil test directs |
| Week 0, before planting | Broadcast Tomato Fertilizer evenly and work it into the soil | Tomato Fertilizer 4-18-38: pounds of potash (K₂O) your soil test recommends ÷ 0.38. Once per season, then retest |
| Week 0, planting day | Water the transplants in; mulch 2 to 3 inches deep[4] | Epsom Salt for Plants transplant drench, 1 tbsp per gallon, only where magnesium is low |
| Weeks 3 to 4 | First Calcium Nitrate sidedress, 4 to 6 inches from the plants, then water it in | Program A: 1 lb per 100 sq ft (45 g per 10 sq ft), or 1 lb per 30 ft of row, once. On sandy soil, split into two halves 3–4 weeks apart |
| Weeks 6 to 8, sandy soil only | Second half of the Program A sidedress | The other half of the Program A amount |
| Monthly, instead of Program A | Program B: a monthly row sidedress, 4 to 6 inches from the plants, watered in | 2 lb per 100 ft of row, applied monthly: 91 g (0.2 lb) per 10 ft of row per application |
| Every week | Water deeply and evenly; keep the mulch in place | About 1 to 2 inches of water per week, depending on the soil (University of Georgia) |
| Only if a soil or leaf test shows low magnesium | Epsom Salt for Plants in the soil or on the leaves | Soil: 1 tablespoon per foot of plant height, worked into the soil around the base and watered in, monthly during the growing season. Foliar: 1 tbsp per gallon, every 2 weeks, early morning or evening |
Pick one Calcium Nitrate program, not both. Program A is Clemson's tomato fact sheet: one application three to four weeks after planting, split in two on sandier soil to reduce losses to leaching[2]. Program B is the monthly row rate that Clemson's blossom end rot guidance describes as usually the best choice of sidedress for tomatoes[3]. Neither source gives a start week for Program B; Clemson's tomato fact sheet begins its sidedress three to four weeks after planting. Adjust either program to your soil test. These are South Carolina and Georgia home-garden rates; where your own state Extension service publishes a different rate for tomatoes, follow it.
Worked example (from the Calcium Nitrate page): 25 ft of tomato row at the monthly rate of 2 lb per 100 ft: 25 × 0.02 = 0.5 lb, which is 226.8 g of product supplying 35.2 g of nitrogen and 43.1 g of calcium.
Why the sidedress is calcium nitrate
Tomato Fertilizer 4-18-38 carries little nitrogen and no calcium, so the in-season nitrogen comes from another fertilizer. Clemson advises against ammoniacal nitrogen fertilizers (it names ammonium sulfate, ammonium nitrate and 10-10-10) for tomato sidedressing, because ammonium competes with calcium for uptake[3]. Calcium Nitrate 15.5-0-0 is almost all nitrate nitrogen (14.5% of its 15.5%) and brings 19% calcium with it. More is not better: Oregon State Extension notes that excessive nitrogen can lead to vigorous shoot growth and increase the risk of blossom end rot[8].
Drip lines and plastic mulch
On plastic mulch, the Tomato Fertilizer page describes splitting the potash in two: half broadcast in the bed before laying the mulch, half fed through the drip line during the season. For calcium through drip, University of Georgia Extension begins soluble calcium injections at bloom and continues until fruit is about golf-ball size[5]; it gives no rate, so size the injection from your recipe or follow the label.
Into the harvest
Feeding does not have to stop when the first fruits color. University of Georgia Extension starts its home-garden sidedress once the first fruits are about the size of a quarter and repeats it every three to four weeks "until harvest is completed"[4]. Neither Calcium Nitrate program gives an end date, so for the final weeks follow the label, and skip any extra nitrogen beyond the program.
Feet of row are not square feet
Clemson equates 100 sq ft of garden with about 30 ft of row, so "1 lb per 100 sq ft" and "2 lb per 100 ft of row" are different amounts. Weigh the product rather than scooping it. If you broadcast it, water overhead afterward to wash granules off the leaves, and keep sidedress fertilizer 4 to 6 inches from the stems to avoid burning the roots[2].
Containers
Containers, stage by stage.
A pot holds a small root zone that dries out fast and loses nutrients every time water drains through it, so container tomatoes are fed from a solution rather than a once-a-season soil dose.
Set up the pot
Iowa State University Extension gives standard tomatoes at least a 4-gallon pot (about 12 to 14 inches across) and cherry tomatoes at least 2 gallons, in a mix that drains well yet does not dry out too fast[9]; Texas A&M AgriLife calls 5-gallon containers the most suitable size for tomatoes[10]. Containers may need watering every day. Water until the excess drains out of the bottom: University of Maryland Extension points out that watering leaches nutrients from containers, and that too much fertilizer builds up salt[11].
Feed from the kit chart
The kit's feeding chart is written for nutrient solutions in hydroponic and container systems, so container plants use the same stages and the same grams per gallon as hydroponics. Pick the Standard or Soft water recipe for your water, weigh each part for the current stage from the feeding chart below, dissolve the Calcium Nitrate separately, and water the solution through the pot until a little drains from the bottom.
Example: 5 gallons of Standard recipe at stage 1 is 12.1 g Tomato Fertilizer, 5.7 g Calcium Nitrate and 7.6 g Epsom Salt. For batches under 5 gallons, use a scale that reads to 0.01 g. Because the solution already contains the Calcium Nitrate, container plants on the kit do not also get the bed sidedress.
How often?
The kit page gives the strength for each stage but does not say how often to feed a potting-mix container with it, and the Tomato Fertilizer page gives no container rate of its own. Until those pages do, follow the label for frequency, or email your container size and mix to questions@greenwaybiotech.com or call (562) 351-5168, Monday to Friday, 9 AM to 3 PM Pacific, and we will work it out with you.
Keep salts from building up
Texas A&M AgriLife lists marginal burning or firing of the leaves as a sign of high salts in container mix, and corrects it by leaching the container with tap water at regular intervals[10]. Iowa State adds that blossom end rot and fruit cracking are common when container watering is inconsistent[9], so keep container watering steady through the season.
Soilless Systems
Hydroponics, cluster by cluster.
With no soil to buffer the supply, every nutrient comes from the solution. The kit chart follows the University of Florida IFAS hydroponic tomato formula built on a 4-18-38 premix, recalculated from Greenway's guaranteed analyses.
Grams per US gallon of finished solution. Multiply by the gallons in your batch and weigh each product separately; for batches under 5 gallons, use a scale that reads to 0.01 g. Move to the next stage when the plants reach the next flower cluster, not by the calendar.
| Stage | From | Tomato Fertilizer | Calcium Nitrate | Epsom Salt |
|---|---|---|---|---|
| 1 | Transplant to first flower cluster | 2.42 | 1.13 | 1.51 |
| 2 | First to second cluster | 2.42 | 1.44 | 1.51 |
| 3 | Second to third cluster | 2.42 | 1.81 | 1.51 |
| 4 | Third to fifth cluster | 2.42 | 2.49 | 1.81 |
| 5 | Fifth cluster to end of crop | 2.42 | 3.10 | 1.81 |
| Stage | From | Tomato Fertilizer | Calcium Nitrate | Epsom Salt |
|---|---|---|---|---|
| 1 | Transplant to first flower cluster | 1.44 | 1.34 | 1.51 |
| 2 | First to second cluster | 1.44 | 1.58 | 1.51 |
| 3 | Second to third cluster | 1.80 | 1.98 | 1.51 |
| 4 | Third to fifth cluster | 1.80 | 2.49 | 1.81 |
| 5 | Fifth cluster to end of crop | 2.42 | 3.10 | 1.81 |
For the batch size, stage and recipe you need, the kit calculator does the multiplication and gives a mixing card to download.
How to mix a batch
- Fill the reservoir. Add the full batch of water at room temperature.
- Weigh each product on its own. Example: 5 gallons of Standard, stage 1, is 12.1 g Tomato Fertilizer, 5.7 g Calcium Nitrate and 7.6 g Epsom Salt.
- Add the Epsom Salt, then the Tomato Fertilizer. Stir each into the reservoir until the water is clear.
- Dissolve the Calcium Nitrate separately. Use a clean container with about 1 quart of water per 5 gallons of batch, then pour it slowly into the reservoir while stirring.
- Check pH and EC. Bring the solution to pH 5.8 to 6.2 with a pH-down product, and write down the EC with the date and stage.
- Keep it fresh. Check pH and EC daily and replace the solution every two weeks, as Oklahoma State University Extension advises[13].
Never combine the concentrates
Ohio State University keeps the calcium portion of a tomato solution separate from the other macronutrients in concentrated form, because calcium reacts with sulfate and phosphate to form very insoluble precipitates[12]. In practice, that sediment can clog drip emitters. Once each product is diluted in the reservoir, they can be used together.
Stock tanks for a fertilizer injector
The same recipe as two 30-gallon stock tanks, each injected at 1:100 (1 gallon of each stock per 100 gallons of finished solution). Tank A holds Tomato Fertilizer and Epsom Salt; tank B holds Calcium Nitrate only. These amounts are larger than the kit, so buy the products in their larger sizes.
| Stage | Standard: tank A | Standard: tank B | Soft water: tank A | Soft water: tank B |
|---|---|---|---|---|
| 1 | 16 lb Tomato + 10 lb Epsom | 7.5 lb Calcium Nitrate | 9.5 lb Tomato + 10 lb Epsom | 9 lb Calcium Nitrate |
| 2 | 16 lb Tomato + 10 lb Epsom | 9.5 lb Calcium Nitrate | 9.5 lb Tomato + 10 lb Epsom | 10.5 lb Calcium Nitrate |
| 3 | 16 lb Tomato + 10 lb Epsom | 12 lb Calcium Nitrate | 12 lb Tomato + 10 lb Epsom | 13 lb Calcium Nitrate |
| 4 | 16 lb Tomato + 12 lb Epsom | 16.5 lb Calcium Nitrate | 12 lb Tomato + 12 lb Epsom | 16.5 lb Calcium Nitrate |
| 5 | 16 lb Tomato + 12 lb Epsom | 20.5 lb Calcium Nitrate | 16 lb Tomato + 12 lb Epsom | 20.5 lb Calcium Nitrate |
Fill each tank about two-thirds with water, dissolve the products (Tomato Fertilizer before Epsom Salt in tank A), and top off to 30 gallons. Inject both at the same time so they meet only after dilution, and remake both tanks when the crop moves to the next stage. If two 1:100 injectors run side by side on one water line, UF/IFAS doubles the stock amounts.
Adjust for what is already in your water
| In your water | Adjustment |
|---|---|
| Magnesium | Use 0.039 g less Epsom Salt per gallon for each ppm. For example, 20 ppm magnesium means 0.77 g per gallon less. |
| Potassium | Use 0.012 g less Tomato Fertilizer per gallon for each ppm. This also lowers phosphorus in the same proportion. |
| pH above 6.5 or high alkalinity | Bring the finished solution to pH 5.8 to 6.2, the UF/IFAS target, with an acid pH-down product. |
| Calcium | Do not cut the Calcium Nitrate. UF/IFAS warns that cutting it too far can bring blossom-end rot unless the water supplies the calcium; the calcium in your water adds to the recipe rather than replacing it. |
From the fertilizer alone, the Standard recipe stays under the UF/IFAS 150 ppm calcium target until stage 5; the formula counts on calcium from the water to close part of that gap[1]. Molybdenum comes out at about a tenth of the UF/IFAS target; growers who want to make up the difference can add Sodium Molybdate, sold separately, at the amount on its label.
pH and EC targets
5.8–6.2 Target pH for a hydroponic tomato solution (UF/IFAS)
UF/IFAS sets the final solution at pH 5.8 to 6.2[1], and the kit follows that range. UF/IFAS gives no EC target. Ohio State puts a stage 1 tomato solution at about 2.0 dS/m and stage 3 closer to 2.4, higher when the source water itself carries salts[12]; Oklahoma State lists 2.0 to 4.0 mS/cm for tomatoes, at pH 6.0 to 6.5[13]. The kit's fertilizer adds an estimated 1.0 to 1.7 dS/m across the stages, and your water adds its own, so measure the finished solution rather than relying on these figures.
Setting up a system?
Our step-by-step hydroponic tomatoes guide covers system choice, spacing and trellising. For feeding amounts, use the chart above.
Calcium & Water
Calcium, water and blossom end rot.
Blossom end rot is a calcium disorder of the fruit, not an infection, and in most gardens it is a water problem before it is a fertilizer problem.
The UC Statewide IPM Program describes blossom end rot as the result of a low level of calcium in the fruit and the water balance in the plant, aggravated by high soil salt or low soil moisture and more common on sandier soils[6]. Calcium moves up with water in the xylem; University of Georgia Extension notes that it cannot flow from the leaves through the phloem to developing fruit, that soil-moisture swings such as a week of off-and-on rain can trigger the disorder, and that once it develops in a fruit it cannot be reversed[5]. Penn State Extension adds that it is rarely accompanied by a lack of calcium in the soil[7]. For the full picture of how calcium travels in the plant, see What's the Function of Calcium in Plants?
That is why the program leans on the water as much as the fertilizer. On the fertilizer side, it supplies calcium through Calcium Nitrate rather than adding ammonium sidedress nitrogen, which competes with calcium for uptake; it uses Epsom Salt in beds only where a recent soil report shows magnesium is short, as Clemson advises; and in solutions, the Soft water recipe holds potassium down where the water brings little calcium[1][3]. On the water side, UC IPM advises keeping the root zone from either drying out or staying saturated, and UGA prefers one or two heavy soakings a week to many light sprinklings[4][6]. Calcium sprays are not part of it: UGA Extension finds the research on foliar calcium very inconclusive and supplies calcium through the irrigation water instead[5].
When to change the schedule
| What you see | What to change |
|---|---|
| First fruits with a dark, sunken patch at the blossom end | Check watering first. In beds, confirm the Calcium Nitrate sidedress went on and no ammonium fertilizer was added. In solutions, confirm the recipe matches your water's calcium. Remove affected fruit; it will not recover |
| Tall, leafy plants setting few fruits | Do not add nitrogen beyond the program; excess nitrogen drives shoot growth |
| Scorched leaf edges on container plants | Possible salt build-up: leach the pot with plain water before the next feeding |
| Sandy, fast-draining soil | Use Program A's split: half at weeks 3–4, the other half 3–4 weeks later |
| Yellowing between the veins of older leaves | Possible magnesium shortage: confirm with a soil or leaf test before using Epsom Salt for Plants at the rates on its page |
| Yellowing lower leaves, older leaves first | Many causes besides nutrition; see our guide to yellow leaves on tomato plants before changing the program |
| Solution pH climbing above 6.5 | Bring it back to 5.8 to 6.2 with a pH-down product; check daily |
Key takeaways
- Beds: Tomato Fertilizer once, before planting, at your soil-test amount; then Calcium Nitrate as a sidedress from 3–4 weeks after planting, on one Clemson program
- Containers and hydroponics: weigh all three kit parts into a solution by stage, and change stages by flower cluster, not by date
- Pick the Standard or Soft water recipe from a water test; low-calcium water needs the Soft water recipe
- Dissolve the Calcium Nitrate on its own; never combine the concentrates
- Steady moisture and mulch do as much against blossom end rot as any fertilizer
Common Questions
Frequently asked questions.
How often should I fertilize tomatoes?
It depends on the system. In garden beds, Tomato Fertilizer 4-18-38 goes in once before planting at the amount your soil test sets, and Calcium Nitrate follows as a sidedress: either once, 3 to 4 weeks after planting, or monthly along the row, following Clemson Extension. In hydroponics, check pH and EC daily and replace the solution every two weeks. For containers, the kit page gives the strength for each stage but not how often to apply it, so follow the label.
When should I start fertilizing tomato transplants?
In beds, the pre-plant Tomato Fertilizer is already in the soil at planting, and Clemson Extension sidedresses Calcium Nitrate 3 to 4 weeks after planting. In containers and hydroponics, the stage 1 solution starts at transplant and runs until the first flower cluster. The kit chart gives no rate for seedlings before transplant, so follow the label for those.
Can I use the Complete Tomato Feeding Kit in a garden bed?
Its feeding chart is written for nutrient solutions in hydroponic and container systems. In a bed, use the parts separately: size Tomato Fertilizer by a soil test and work it in before planting, sidedress Calcium Nitrate during the season, and use Epsom Salt only if a soil or leaf test shows low magnesium.
Should I use the Standard or the Soft water recipe?
Use Standard if your water has 50 ppm calcium or more, as most well water and hard tap water do. Use Soft water if it has less, as reverse osmosis, rain and soft tap water do. UF/IFAS warns that excess potassium with water below 50 ppm calcium can bring early blossom end rot, which is why the Soft water recipe uses less Tomato Fertilizer in the early stages. If you are not sure, test your water or ask your water utility for its report.
Can I mix all three products together?
Not as concentrates. Dissolve the Epsom Salt and the Tomato Fertilizer in the reservoir, dissolve the Calcium Nitrate in a separate container of water, then pour it in while stirring. Concentrated calcium reacts with phosphate and sulfate and settles out, which can clog drip emitters. Once each is diluted in the full batch, they can be used together. In a garden bed, apply them as separate feedings.
When do I move to the next stage?
When the plants reach the next flower cluster, not by the calendar. Stage 2 starts at the first cluster, stage 3 at the second, stage 4 at the third and stage 5 at the fifth, which runs to the end of the crop.
Should I stop feeding once tomatoes start to ripen?
Not in a solution: stage 5 of the kit chart, the strongest, runs from the fifth flower cluster to the end of the crop. In beds, University of Georgia Extension repeats its home-garden sidedress every three to four weeks until harvest is completed. Oregon State Extension cautions that excessive nitrogen can lead to vigorous shoot growth and raise the risk of blossom end rot, so stay with the program amounts rather than adding more.
Will this program prevent blossom end rot?
No fertilizer program can promise that. Blossom end rot is a calcium disorder of the developing fruit, and university guides tie it mostly to uneven soil moisture rather than a shortage of calcium in the soil. Keep the root zone evenly moist, mulch beds, avoid ammonium-based sidedress fertilizers, and supply calcium as the program does. Affected fruit cannot recover, so remove it and correct the cause.
Can I use the kit on peppers or other crops?
Only on crops the package labels name. Tomato Fertilizer contains boron, which can injure crops its label does not list, and molybdenum, so never use it on forage or pasture. The feeding chart in this article is calculated for tomatoes.
Build the Program
The products in this program.
The program
Complete Tomato Feeding Kit
All three parts in separate bags, sized to run out together, with the Standard and Soft water feeding charts. Starter and Season sizes.
Tomato Fertilizer 4-18-38
Phosphate, potash and EDTA-chelated micronutrients. Before planting in beds, by soil test; in every batch of solution.
Calcium Nitrate 15.5-0-0
Nitrate nitrogen and 19% calcium. The bed sidedress, and the part dissolved on its own in every solution.
Epsom Salt for Plants
Magnesium and sulfur. A fixed part of the solution recipes; in beds, only where magnesium tests low.
Each part is also sold on its own in larger sizes for injector stock tanks or bigger plantings. Already running a different base nutrient on reverse-osmosis water? Cal-Mag Plus 2-0-0 supplies calcium, magnesium and chelated iron at its label rate of 5–10 mL of concentrate per gallon of reservoir. The kit's two recipes are built without it, so it is not needed on top of them.
About This Guide
Review & sources.
Written by the Greenway Biotech Team.
Reviewed by Amir Tajer, B.S.M.E., QAL — Co-Owner & Technical Director, Greenway Biotech, Inc. Reviewed against UF/IFAS Extension, Clemson Cooperative Extension, University of Georgia Extension, UC Statewide IPM Program, Penn State Extension, Oregon State University Extension, Iowa State University Extension, Texas A&M AgriLife Extension, University of Maryland Extension, Ohio State University and Oklahoma State University Extension guidance. Every fertilizer rate, mixing amount and feeding frequency in this article is taken from the live Greenway product pages for the Complete Tomato Feeding Kit, Tomato Fertilizer 4-18-38, Calcium Nitrate 15.5-0-0, Epsom Salt for Plants and Cal-Mag Plus 2-0-0; stage timing, watering and the agronomy behind them come from the university sources below. The label on your package governs, and if it differs from this article, contact us before applying. Rates and sources reviewed November 4, 2026. This guide replaces our 2022 article, Easy Tips to Fertilize Your Tomatoes for Better Yields.
Disclosure: Greenway Biotech sells the products discussed in this program. Greenway Biotech, Inc. has been family-owned in California since 1989 and is a CDFA-registered fertilizer manufacturer. The products in this program are packed in Madera, California. Heavy-metal test results are posted on our lab tests page.
Questions about your soil test, water or setup? Email questions@greenwaybiotech.com or call (562) 351-5168, Monday to Friday, 9 AM to 3 PM Pacific.
Sources:
- Nutrient Solution Formulation for Hydroponic (Perlite, Rockwool, NFT) Tomatoes in Florida (HS796/CV216) — UF/IFAS Extension
- Tomato (HGIC 1323) — Clemson Cooperative Extension, Home & Garden Information Center
- Tomato Diseases & Disorders (HGIC 2217) — Clemson Cooperative Extension, Home & Garden Information Center
- Georgia Homegrown Tomatoes (B 1271) — University of Georgia Cooperative Extension
- Blossom-End Rot and Calcium Nutrition of Pepper and Tomato (C 938) — University of Georgia Cooperative Extension
- Blossom End Rot — UC Statewide IPM Program, University of California Agriculture and Natural Resources
- Blossom End Rot, Internal Whitening, and Rain Check of Tomatoes — Penn State Extension
- Feed Your Vegetable Garden Midseason to Boost Growth and Yields — Oregon State University Extension Service
- Growing Tomatoes in Containers — Iowa State University Extension and Outreach
- Vegetable Gardening in Containers (E-545) — Texas A&M AgriLife Extension
- Maintaining Container Grown Vegetables — University of Maryland Extension
- Hydroponic Nutrient Solution for Optimized Greenhouse Tomato Production (HYG-1437) — Ohio State University Extension
- Electrical Conductivity and pH Guide for Hydroponics (HLA-6722) — Oklahoma State University Extension
Ready to Feed
Three parts, one season of feeding.
Shop the Complete Tomato Feeding Kit
| Family-owned | In California since 1989 |
|---|---|
| CDFA-registered | Fertilizer manufacturer |
| Packed in | Madera, California |
| Lab tests | Heavy-metal results |
| Contact | questions@greenwaybiotech.com |
| Phone | (562) 351-5168 |
| Hours | Monday to Friday, 9 AM to 3 PM Pacific |
