Plant tomatoes after your last spring frost, when soil reaches 60°F

The single most important date for tomato planting is your area's last spring frost date. Tomatoes are killed by frost—even a light one—so planting before that date wastes the seedling. You can find your frost date by searching "[your city] last frost date" or by entering your zip code at the National Weather Service website or Almanac.com.

Beyond frost safety, soil temperature matters as much as air temperature. Tomato seeds and transplants sit dormant or rot in cold soil. Soil should reach at least 60°F, though 65°F to 70°F is ideal for faster growth. You can measure soil temperature with a straightforward soil thermometer from any garden center—stick it 4 inches into the ground in the morning.

If you live in a very warm climate where frost never arrives, you can plant tomatoes in late summer or early fall instead, timing them to mature before extreme heat arrives in midsummer.

Key Takeaways

  • Your last spring frost date is the hard important date—tomatoes planted before it will be killed by cold, so check your local date before buying seedlings.
  • Soil temperature of 60°F or higher matters more than air temperature, and you can measure it with an inexpensive soil thermometer.
  • Seedlings started indoors 6 to 8 weeks before your frost date will be ready to transplant right when conditions are safe.
  • In warm climates with no spring frost, plant tomatoes in late summer so they mature before peak heat arrives.
  • Hardening off—gradually exposing indoor seedlings to outdoor conditions—takes 7 to 10 days and must happen before transplanting.

Starting seeds indoors 6 to 8 weeks before your frost date

If you want to start tomatoes from seed, begin indoors 6 to 8 weeks before your last spring frost date. This gives seedlings time to develop true leaves and a small root system before moving outdoors. A seedling started too early will become leggy and weak while waiting for warm soil; one started too late will still be tiny when planting time arrives.

Tomato seeds germinate best in warm soil—70°F to 75°F—under grow lights or in a sunny window. They sprout in 5 to 10 days. Once they have their first true leaves (the second set to appear), thin them so each seedling has its own small pot. Keep the soil moist but not waterlogged, and provide 14 to 16 hours of light daily.

About a week before your frost date, begin hardening off: move seedlings outside to a sheltered spot for a few hours, then gradually increase their time outdoors over 7 to 10 days. This toughens them against wind and direct sun. After hardening off, they are ready to transplant into the garden.

Buying transplants and planting them at the right time

Many gardeners buy tomato transplants from a nursery rather than starting seed. Look for stocky, dark-green seedlings with visible roots at the drainage holes—avoid tall, pale, or leggy plants. Transplants are usually ready to plant 1 to 2 weeks after your frost date, once soil has warmed.

Before planting, harden off nursery transplants the same way you would homegrown ones: expose them to outdoor conditions gradually over a week. Even though they were grown in a greenhouse, the shock of full sun and wind can stall their growth if they are not acclimated first.

Plant transplants deeper than they were growing in their pot—bury the stem up to the first true leaves. Tomatoes will root along the buried stem, creating a stronger root system. Space plants 24 to 36 inches apart depending on variety, and water well after planting.

Timing for different tomato varieties

Determinate (bush) tomatoes mature all at once, usually 60 to 75 days after transplanting. Plant them all on the same day if you want a concentrated harvest for canning or sauce-making. Indeterminate (vining) tomatoes produce fruit continuously until frost kills the plant, taking 70 to 85 days to first fruit. You can stagger plantings of indeterminate varieties 2 to 3 weeks apart for a longer harvest window.

Cherry and heirloom tomatoes often take longer to mature—80 to 90 days—so plant them earlier in the season if your growing season is short. Paste tomatoes (like San Marzano) are usually determinate and good for single-harvest planting.

Adjusting for short growing seasons

If you live in a northern climate with a short frost-free period, start seeds indoors earlier—8 to 10 weeks before your frost date instead of 6 to 8. Choose fast-maturing varieties that reach harvest in 60 to 70 days. Use black plastic mulch or landscape fabric to warm the soil before planting, and consider using row covers or cloches to protect young plants from unexpected cold snaps.

In very short seasons, you may need to start seeds indoors under lights in late winter (February or early March in many northern areas) to have transplants ready by late May or early June. Waiting until soil warms naturally may leave you with no time for fruit to mature before fall frost arrives.

Protecting transplants from late frost

Even after you plant, a surprise frost can arrive. Keep frost cloth, row covers, or old blankets on hand during the first 2 to 3 weeks after planting. If frost is forecast, cover plants in the evening and remove covers the next morning once temperatures rise above 50°F.

Watering the soil (not the leaves) the evening before a frost can also help—moist soil holds heat better than dry soil. Avoid fertilizing newly planted tomatoes until they are established and growing; nitrogen pushes leaf growth over root development, making plants more vulnerable to stress.

Container and greenhouse planting

If you are growing tomatoes in containers, you can plant slightly earlier than in-ground gardens because you can move pots to a sheltered spot or indoors if frost threatens. Containers warm up faster than garden soil in spring, but they also cool down faster in fall. Use containers at least 5 gallons for determinate varieties and 10 gallons for indeterminate types.

In a greenhouse or cold frame, you can plant 2 to 3 weeks earlier than outdoor gardens because the structure traps heat. However, you still need to monitor soil temperature and may support good air circulation to prevent fungal disease.

Frequently Asked Questions

What if I plant tomatoes too early and frost kills them?

You will need to start over. Frost-killed tomato plants cannot recover. To avoid this, always wait until after your last frost date and soil reaches 60°F. If you are eager to plant, use row covers or cloches to protect young plants for the first few weeks.

Can I plant tomatoes in summer if I missed the spring window?

In most climates, no—tomatoes planted in mid or late summer will not have enough time to mature before fall frost. In warm southern regions with long growing seasons, you can sometimes plant a second crop in midsummer for fall harvest, but check your first-frost date to be sure.

How do I know if my seedlings are ready to transplant?

Seedlings are ready when they have 4 to 6 true leaves (not the first rounded seed leaves), are 6 to 8 inches tall, and have visible roots at the drainage holes. They should be hardened off before moving to the garden.

Do I need to wait for soil to warm if I use black plastic mulch?

Black plastic warms soil faster, so you can plant 1 to 2 weeks earlier than you could without it. However, still wait until after your frost date and check that soil temperature has reached at least 60°F before planting.

What happens if I plant tomatoes in cold soil?

Cold soil slows root development and can cause seeds to rot. Transplants will sit dormant and may yellow or wilt. Growth will be stunted even after soil warms. Always wait for soil temperature to reach 60°F or higher.