How to Grow Tomatoes From Seed

Tomatoes are warm-season plants that cannot take frost, so timing matters. Start seeds indoors 6 to 8 weeks before your average last frost. Transplant outside only after all danger of frost has passed, the soil has warmed to at least 60F, and nights stay above 50F. In cold-winter regions that means late spring; in hot, long-season climates like the Gulf Coast, Florida, and the Southwest you can grow both a spring and a fall crop, skipping the peak of summer heat when tomatoes stop setting fruit.

Sow seeds a quarter inch deep in a warm, moist seed-starting mix and keep them at 70 to 80F until they sprout in 5 to 10 days. Give seedlings bright light for 14 to 16 hours a day and a weekly half-strength feed once true leaves appear, potting them up as they grow. About 6 to 8 weeks later, after hardening them off over a week, transplant into full sun, setting each plant deep so two-thirds of the stem is buried, since tomatoes root all along a buried stem. Space bush types 18 to 24 inches apart and vining types 24 to 36 inches, and add a stake or cage at planting time.

Tomatoes are hungry, thirsty plants that reward steady care. Water deeply and evenly, about 1 to 2 inches a week, always at the base, and mulch to keep moisture even and stop soil splashing up that spreads disease. Feed at planting and again once fruit sets with a balanced or slightly lower-nitrogen fertilizer, since too much nitrogen gives leaves instead of fruit. Stake or cage plants and tie them up as they grow. On vining (indeterminate) types, pinching out the small side shoots between the main stem and branches keeps plants open, healthy, and productive.

Tomatoes grow well with plants that repel their pests, draw in pollinators, or share their love of rich soil and sun. Basil is the classic partner, and marigolds, nasturtiums, carrots, and onions all help too. These three are especially easy to add in one click:

Pick tomatoes when they are fully colored and give slightly to a gentle squeeze, cutting or gently twisting them free. For the best flavor ripen them on the vine, but you can also harvest at the breaker stage, when color just begins, and finish them at room temperature indoors, never in the fridge, which dulls flavor and texture. As the season ends, gather all the mature green fruit before the first hard frost and ripen it on a counter or windowsill.

Home-grown tomatoes are the heart of summer cooking. Slice beefsteaks for sandwiches and burgers, toss cherry and pear types whole into salads and roasting pans, and cook down paste tomatoes like Roma into rich sauces, salsas, and passata for the winter pantry. They can, freeze, and dry beautifully, and are loaded with vitamin C and the antioxidant lycopene. A few well-tended plants can feed a kitchen from midsummer to frost.

• Blossom drop: flowers fall without setting fruit, usually from heat over 90F, cold nights below 55F, or dry soil. Keep watering even and wait for milder temperatures.
• Blossom-end rot: a sunken brown patch on the base of the fruit from uneven watering and calcium uptake. Water consistently, mulch, and go easy on high-nitrogen feeds.
• Cracking and splitting: caused by a big drink after a dry spell. Water deeply and evenly and mulch to buffer soil moisture.
• Leggy, pale seedlings: too little light. Give seedlings 14 to 16 hours of bright light and pot them up deeply.
• Leaf spots and blight: fungal diseases spread by wet leaves. Water at the base, mulch, space for airflow, and remove affected lower leaves.
• Hornworms: large green caterpillars that strip leaves fast. Pick them off by hand and let beneficial wasps help.