Start seeds indoors 6 to 8 weeks before your last spring frost

The fastest way to a tomato plant is to buy a seedling from a garden center, but growing from seed costs less and gives you more varieties to choose from. Start seeds indoors in late winter or early spring — the exact timing depends on when your last frost date falls, which you can find by entering your zip code into the USDA Hardiness Zone map on planthardiness.ars.usda.gov.

Fill a seed tray or small pots with seed-starting mix (a light, sterile soil blend), dampen it, and press one or two tomato seeds about a quarter-inch deep into each cell. Cover the tray loosely with plastic wrap or a humidity dome to keep moisture in. Place it in a warm spot — tomato seeds germinate best between 70 and 80 degrees Fahrenheit. They should sprout in 5 to 10 days.

Once seedlings emerge, remove the cover and move them to a bright window or under grow lights positioned 2 to 3 inches above the leaves. Keep the soil moist but not waterlogged. When seedlings develop their first true leaves (the second set to appear), thin them so only the strongest one remains per cell, or transplant each into its own small pot.

Key Takeaways

  • Tomato seeds need warmth to sprout and bright light once they emerge, so start them indoors under grow lights or in a sunny window 6 to 8 weeks before your last frost date.
  • Harden off seedlings by gradually exposing them to outdoor conditions over 7 to 10 days before transplanting them into the garden.
  • Plant seedlings deep — bury the stem up to the first true leaves, because tomatoes will root along the buried stem and develop a stronger plant.
  • Tomatoes need at least 6 to 8 hours of direct sun daily, consistent watering (about 1 to 2 inches per week), and support from a cage, stake, or string as they grow.
  • Pick fruit when it reaches full color but is still slightly firm, or pick green tomatoes before frost and ripen them indoors on a windowsill.

Harden off seedlings before moving them outside

Seedlings grown indoors are tender and will wilt or die if you move them straight into the garden. Instead, spend 7 to 10 days gradually exposing them to outdoor conditions — a process called hardening off. Start by placing seedlings in a sheltered, shaded spot outdoors for 2 to 3 hours on the first day. Each day, increase their time outside and gradually move them into more direct light.

By the end of the hardening-off period, seedlings should spend a full day and night outside before transplanting. This toughens the leaves and stems so they can handle wind, sun, and temperature swings. If frost threatens during this time, bring seedlings back indoors.

Transplant seedlings into the garden after the last frost date

Once seedlings are hardened off and nighttime temperatures stay above 50 degrees Fahrenheit, they are ready for the garden. Choose a spot that receives at least 6 to 8 hours of direct sun — more sun means more fruit and better flavor. Tomatoes are not picky about soil type, but they prefer soil rich in organic matter, so mix compost or aged manure into the planting area before you dig.

Plant seedlings deeper than they grew in their pots. Bury the stem up to the first true leaves or even higher — tomatoes will sprout roots all along the buried stem, creating a stronger root system. Space plants 24 to 36 inches apart depending on the variety (determinate types stay compact; indeterminate types grow tall and sprawling). Water gently after planting and keep the soil consistently moist for the first week.

Water deeply and regularly throughout the growing season

Tomatoes need steady moisture to produce fruit and prevent problems like blossom-end rot (a dark spot on the bottom of the fruit caused by calcium deficiency linked to irregular watering). Water deeply at the base of the plant rather than overhead — wet leaves invite fungal disease. Aim for 1 to 2 inches of water per week, either from rain or irrigation.

In hot weather, you may need to water every 2 to 3 days. Mulch around plants with 2 to 3 inches of straw or shredded leaves to help soil retain moisture and keep roots cool. Avoid letting soil dry out completely between waterings, and do not overwater — soggy soil can cause root rot and crack fruit.

Support plants with cages, stakes, or string as they grow

Tomato plants need support to keep fruit off the ground and improve air circulation around leaves. Install support early — within a week or two of transplanting — so you do not damage roots later. A cage made of sturdy wire works for most plants, but tall indeterminate varieties often outgrow cages and do better with stakes or string.

For stakes, drive a 5- to 6-foot wooden or metal stake into the ground near the plant and tie the main stem loosely to it as it grows, using soft ties or strips of cloth. For string support (common in commercial greenhouses), tie string to an overhead beam or trellis and loop it around the plant stem every 8 to 12 inches as the plant grows taller. Prune suckers — shoots that grow between the main stem and branches — on indeterminate varieties to direct energy into fruit production.

Fertilize every 2 to 3 weeks once flowering begins

Tomato seedlings benefit from a diluted liquid fertilizer every 1 to 2 weeks while growing indoors, but once they are in the garden, soil usually provides enough nutrients for the first few weeks. Once flowers appear, switch to a fertilizer higher in phosphorus and potassium (the second and third numbers on a fertilizer label) to encourage fruiting. A balanced fertilizer like 5-10-10 or a tomato-specific formula works well.

explore fertilizer every 2 to 3 weeks according to package directions. Avoid high-nitrogen fertilizers, which produce leafy plants with few fruit. If you mixed compost into the soil at planting time, you may not need much additional fertilizer — compost releases nutrients slowly over the season.

Harvest fruit when it reaches full color

Tomatoes are ready to pick when they reach their mature color — red, pink, orange, yellow, or whatever the variety produces — and yield slightly to gentle pressure. You do not have to wait for them to be soft; slightly firm fruit stores better and continues to ripen after picking. Twist and lift gently, or use pruning shears to avoid damaging the plant.

If frost threatens before all fruit ripens, pick all remaining tomatoes — even green ones — and ripen them indoors. Place them in a single layer on a windowsill or in a paper bag with a ripe banana or apple (which releases ethylene gas and speeds ripening). Green tomatoes ripen best between 68 and 77 degrees Fahrenheit and will turn color in 1 to 3 weeks. Tomatoes picked after they have started to blush (show a hint of color) ripen faster than fully green ones.

Frequently Asked Questions

Why are my tomato flowers falling off without making fruit?

Flowers drop when temperatures fall below 55 degrees Fahrenheit at night or exceed 90 degrees during the day, when watering is inconsistent, or when nitrogen fertilizer is too high. may support steady watering, avoid over-fertilizing, and wait for temperatures to stabilize — new flowers will form once conditions improve.

What is the white powder on my tomato leaves?

That is likely powdery mildew, a fungal disease that thrives in warm, dry conditions with poor air circulation. Improve airflow by pruning lower leaves and spacing plants farther apart. Water at the base only, and spray affected leaves with a sulfur-based fungicide or a baking soda solution (1 tablespoon baking soda plus 1 tablespoon oil and 1 tablespoon dish soap per gallon of water).

Can I grow tomatoes in containers?

Yes. Use a pot at least 5 gallons for determinate varieties and 10 gallons for indeterminate types, fill it with quality potting soil, and place it in full sun. Container tomatoes dry out faster than garden plants, so check soil moisture daily and water when the top inch feels dry. Fertilize every 2 weeks because watering leaches nutrients from containers.

How do I know if my tomato variety is determinate or indeterminate?

The seed packet or plant label will say. Determinate varieties grow to a fixed height (usually 3 to 4 feet), produce most fruit at once, and are good for canning. Indeterminate varieties grow continuously throughout the season, produce fruit until frost, and need taller support — they are better for fresh eating.