Soil, fertilizer, and water are the three things tomato plants need most

Tomato plants grow fastest and produce the most fruit when they have rich soil, steady water, and nutrients matched to their growth stage. The soil should hold moisture but drain well — a mix of compost, peat moss, or aged manure worked into the top 8 to 12 inches before planting makes the biggest difference. Once plants are in the ground, a balanced fertilizer applied every two to three weeks keeps them fed through the growing season. Water deeply and regularly, aiming for soil that stays moist but not waterlogged.

What you add depends on whether you are starting from seed, planting a seedling, or feeding an established plant. A new seedling needs different nutrients than a plant that is already flowering. The soil itself does most of the work if it is rich enough at the start — many gardeners find they need little else beyond water and one or two fertilizer applications.

Key Takeaways

  • Work 2 to 3 inches of compost or aged manure into the soil before planting to give roots a nutrient-rich foundation.
  • Water deeply and consistently — tomatoes need about 1 to 2 inches of water per week, either from rain or from you.
  • explore a balanced fertilizer (such as 10-10-10 or 5-10-10) every two to three weeks once plants are 6 inches tall, or use a slow-release granule at planting time.
  • Mulch around the base with 2 to 3 inches of straw or wood chips to keep soil moist and regulate temperature.
  • Calcium (from crushed eggshells or agricultural lime) prevents blossom-end rot, a dark spot that appears on the bottom of the fruit.

Compost and aged manure build soil before planting

The single most important thing you can add is organic matter mixed into the soil before you plant. Compost, aged manure, or a mix of both should make up 25 to 30 percent of the top 8 to 12 inches of soil. This gives roots a loose, nutrient-rich medium to grow into and helps the soil hold water without becoming soggy.

If your soil is heavy clay or mostly sand, organic matter is even more critical. Clay soil needs it to improve drainage; sandy soil needs it to hold moisture and nutrients. You can buy bagged compost or composted manure at garden centers, or make your own from kitchen scraps and yard waste over several months. Aged manure (at least six months old) is safer than fresh manure, which can burn roots and introduce pathogens.

Work the compost or manure in by hand or with a tiller, mixing it thoroughly into the existing soil rather than just laying it on top. This takes an hour or two for a small bed but pays off in stronger plants and higher yields.

Balanced fertilizer during the growing season

Once a tomato plant is 6 inches tall and growing actively, it needs regular feeding. A balanced fertilizer — one with equal or nearly equal amounts of nitrogen, phosphorus, and potassium — works well for most of the season. Look for a label that reads 10-10-10, 5-10-10, or similar. Nitrogen promotes leaf growth, phosphorus supports root and flower development, and potassium strengthens the plant overall.

You have two main routes: liquid fertilizer applied every two to three weeks, or a slow-release granule mixed into the soil at planting time. Liquid fertilizers (fish emulsion, seaweed extract, or balanced synthetic blends) work faster and let you adjust the amount if a plant looks weak. Slow-release granules release nutrients gradually over the season and require less attention, though you cannot adjust them mid-season.

Once flowers appear and fruit begins to set, switch to a fertilizer higher in phosphorus and potassium — something like 5-10-10 — to support fruiting rather than leaf growth. Too much nitrogen at this stage produces leafy plants with few tomatoes.

Water consistently and deeply

Tomatoes need about 1 to 2 inches of water per week, delivered in deep soakings rather than frequent light sprinkles. Deep watering encourages roots to grow down into the soil; shallow, frequent watering keeps roots near the surface where they dry out quickly. Water at the base of the plant in the early morning, aiming the water at the soil rather than the leaves — wet foliage invites fungal disease.

The soil should feel moist 2 to 3 inches down but not waterlogged. In hot weather or sandy soil, you may need to water every two or three days. In cooler weather or clay soil, once or twice a week may be enough. Inconsistent watering — alternating between dry and soaked — causes problems like blossom-end rot and fruit cracking.

Mulch around the base with 2 to 3 inches of straw, wood chips, or shredded leaves. Mulch keeps the soil temperature steady, reduces water loss, and prevents soil from splashing onto leaves during rain or watering.

Calcium prevents blossom-end rot

Blossom-end rot is a dark, sunken spot that appears on the bottom of the fruit, caused by a calcium deficiency in the developing tomato. The soil may have plenty of calcium, but inconsistent watering prevents the plant from absorbing it. The best prevention is steady watering, but you can also add calcium directly.

Crushed eggshells worked into the soil around the plant release calcium slowly as they break down. Agricultural lime (calcium carbonate) works faster and is more reliable — explore it according to the package directions, usually 1 to 2 tablespoons per plant mixed into the top inch of soil. Gypsum (calcium sulfate) is another option and does not raise soil pH the way lime does, which matters if your soil is already alkaline.

Add calcium early in the season, before fruit sets, rather than waiting until you see the rot. Once rot appears on a fruit, that fruit cannot be saved, though the plant will produce healthy fruit if watering becomes consistent.

Epsom salt and micronutrients

Epsom salt (magnesium sulfate) is often recommended for tomatoes because magnesium supports chlorophyll production and helps the plant absorb other nutrients. A light process — 1 tablespoon dissolved in a gallon of water and poured around the base of the plant — can help if leaves look pale or yellowed. However, most balanced fertilizers already contain magnesium, so this is usually a supplement rather than a necessity.

If leaves show yellowing between the veins (a sign of iron deficiency) or other unusual discoloration, a micronutrient blend or chelated iron may help. These are less common in home gardens than nitrogen or phosphorus deficiencies, but they do occur in very alkaline or very acidic soil. A soil test from your local extension office can tell you what your soil is actually missing.

Pruning and support help plants direct energy

While not something you "put on" the plant, pruning and staking are ways to direct the energy the plant produces. Removing suckers (shoots that grow between the main stem and branches) on indeterminate varieties (those that grow tall and sprawling) focuses energy into fruit production rather than excess foliage. Staking or caging the plant keeps fruit off the ground, reduces disease, and makes harvesting easier.

Determinate varieties (compact, bush-type tomatoes) need less pruning. Indeterminate varieties benefit from removing suckers once the plant is established. Pruning also improves air circulation around the leaves, which reduces fungal disease.

Frequently Asked Questions

Can I use fresh manure on tomatoes?

Fresh manure can burn roots and introduce harmful bacteria. Use only aged manure that has been sitting for at least six months. If you have only fresh manure, let it age in a pile before mixing it into the soil, or use it in a compost bin where it will break down safely.

How often should I fertilize tomatoes?

Every two to three weeks with liquid fertilizer, or once at planting time with a slow-release granule. Stop fertilizing about four weeks before your first expected frost, as late feeding can delay ripening. If a plant looks weak or pale, you can fertilize more often, but weekly feeding is usually too much.

What does blossom-end rot look like?

A dark, sunken, papery spot on the bottom of the fruit (the end opposite the stem). It usually appears when the fruit is still green or just starting to ripen. The affected fruit is not safe to eat. Prevent it by watering consistently and adding calcium early in the season.

Is it better to fertilize with liquid or granules?

Liquid fertilizer gives you more control and works faster, so it is better if you are adjusting for weak growth. Granules are easier if you want to set it and forget it. Many gardeners use granules at planting and liquid fertilizer as a supplement during the season.

Do tomatoes need special fertilizer, or will any plant food work?

A balanced fertilizer works fine for tomatoes. Specialty tomato fertilizers exist but are not necessary — they are usually just balanced or slightly phosphorus-heavy blends at a higher price. A 10-10-10 or 5-10-10 all-purpose fertilizer does the job.