Quick Answer
Feed tomatoes once a week through the growing season, and dose by size. With Tomato Fertilizer, mix 1 tablespoon (15 mL) per gallon of water while plants are under 12 inches, then 2 tablespoons (30 mL) per gallon once they are large or carrying fruit. A hose-end sprayer set to the same rates covers full rows, and you can feed right up to harvest.
How to fertilize tomatoes through the season
Tomatoes are heavy feeders that change what they need as they grow. Early on, a transplant is building a canopy and roots. Once it flowers and sets fruit, the demand shifts to potassium and calcium for filling and ripening. The 3.6-3-5.1 ratio in Tomato Fertilizer is built for that arc: enough nitrogen to build the plant early, then potash leading to set, fill and ripen fruit.
Start a week after transplanting at the lower rate, move to the higher rate when plants pass about 12 inches or set their first fruit, and keep feeding weekly until the plant stops setting new fruit at the end of the season.
| Method | Amount | How often |
|---|---|---|
| Watering can, plants under 12 inches | 1 Tbs (15 mL) per gallon of water | Once weekly |
| Watering can, large or fruiting plants | 2 Tbs (30 mL) per gallon of water | Once weekly |
| Hose-end sprayer | Set the dial to the rate above | Once weekly |
| Leaf misting (optional) | 1 tsp per quart (32 oz) of water | Every 1–2 weeks |
How much fertilizer should you give a tomato plant?
A gallon of mixed feed waters roughly one large plant or two or three young ones; water the root zone until the soil is wet a few inches down, as you would with plain water. Container and grow-bag tomatoes exhaust their potting mix fastest, since every watering carries nutrients out the drainage holes, so keep them on the weekly schedule without skipping.
Liquid vs. granular tomato fertilizer
A granule sits where you spread it and releases over weeks into the soil beneath, so the plant gets a burst, then a long tail, and you cannot adjust either. A liquid goes on across the whole root zone at a strength you set, and the nitrate nitrogen in Tomato Fertilizer is available to the roots as soon as it is watered in. That makes a liquid the better choice when you want a visible response this season, and for containers and raised beds that lose nutrients with every watering.
Signs a tomato plant may be underfed
- Plenty of leaf growth but very few flowers setting fruit
- Lower leaves yellowing and dropping while the plant is still fruiting
- Fruit staying small and slow to ripen on the vine
- Vines that start strong then fade by the middle of summer
Signs you may be fertilizing too much
A tomato that is all vine and no tomatoes is the classic sign of too much nitrogen relative to potash and phosphorus: a rich bed plus a high-nitrogen feed keeps the plant growing leaves. Beyond nutrition, tomatoes drop blossoms in heat above roughly 90°F and will not set well in shade. If your plant is lush and fruitless, stop any extra nitrogen source, keep to the weekly Tomato Fertilizer schedule, and give it full sun.
Does fertilizer prevent blossom end rot?
It helps. Blossom end rot is a calcium shortage at the fruit, and Tomato Fertilizer carries unusually high calcium at 2.1% for that reason. But roots only move calcium in evenly moist soil, so irregular watering causes the problem even when calcium is plentiful; the plant simply cannot deliver it to the fruit. Feed weekly, mulch to even out soil moisture, and water on a schedule. Fruit that sets after you fix both usually comes in clean.
Is it safe to use on tomatoes you are going to eat?
Yes. Tomato Fertilizer is a mineral fertilizer derived from kelp and standard plant nutrient salts, made for edible gardens, with no waiting period before harvest. The nutrients it supplies are the same ones the plant would draw from the soil: nitrate nitrogen, phosphate, potash, calcium, magnesium and trace elements. Rinse tomatoes before eating as you normally would.
