Plant tomatoes after the last frost date in your area, when soil temperature reaches 60°F and ideally stays above 50°F at night

The single most important rule is this: tomatoes cannot survive frost. A hard freeze will kill the plant, and even a light frost will stunt growth and damage fruit. Your local last frost date — the average date of the final frost in spring — is your starting point. You can find this date by entering your zip code at the National Weather Service website or asking your local cooperative extension office.

Soil temperature matters as much as air temperature. Tomato seeds and transplants will sit dormant or rot in cold soil. Soil should reach at least 60°F before you plant, and ideally stay above 50°F at night. A soil thermometer costs $10 to $20 and takes the guesswork out. If you plant too early into cold soil, the roots won't grow, and the plant will struggle all season.

The timing also depends on whether you are starting from seed indoors or buying transplants from a nursery. These two paths have different schedules, and getting the timing wrong on either one means a weak plant or a missed season.

Key Takeaways

  • Plant tomatoes outdoors only after your last frost date has passed and soil temperature is at least 60°F, checked with a soil thermometer.
  • If you start seeds indoors, sow them 6 to 8 weeks before your last frost date so transplants are ready to go into the ground at the right time.
  • Transplants from a nursery can go in the ground as soon as conditions are right, without the 6 to 8 week lead time.
  • Soil that is too cold will cause seeds to rot and transplants to sit dormant; waiting one to two weeks for soil to warm is faster than planting early and waiting.

Starting seeds indoors: the 6 to 8 week timeline

If you want to grow tomatoes from seed, start them indoors 6 to 8 weeks before your last frost date. This gives seedlings time to develop true leaves and a strong root system before they go outside. A tomato seed germinates in 5 to 10 days under warm conditions (70°F to 80°F), and the seedling needs another 6 to 7 weeks to reach transplant size — roughly 6 to 8 inches tall with at least two sets of true leaves.

Use a seed-starting mix (not garden soil) in small pots or trays, keep the soil moist but not waterlogged, and provide 14 to 16 hours of light per day. A grow light or a sunny south-facing window works. Once seedlings have true leaves, thin them so each pot holds one plant. When they reach 6 to 8 inches tall and your last frost date is one to two weeks away, begin hardening them off — moving them outdoors for a few hours each day, gradually increasing time outside over 7 to 10 days. This toughens the plant so it can handle outdoor conditions without shock.

Buying transplants: the faster route

Nursery transplants skip the indoor seed stage entirely. You buy a plant that is already 6 to 8 inches tall and ready to go in the ground. This works well if you do not have indoor space, grow lights, or the time to manage seedlings. The trade-off is cost — transplants run $3 to $8 per plant, while seeds cost $2 to $4 per packet and yield many plants.

Buy transplants one to two weeks before your last frost date so they are available when soil is warm enough. Nurseries often sell them too early in the season, and a plant sitting in a cold greenhouse or on a cold shelf will not thrive. If you buy early, keep the transplant indoors or in a warm spot until planting day. Harden off nursery transplants the same way you would homegrown seedlings — a few hours outside each day for a week — even though they may look sturdy.

Soil temperature and frost date are not the same thing

A common mistake is planting on the last frost date without checking soil temperature. The air can be warm enough, but the soil can still be cold. Soil warms more slowly than air, especially in spring when the ground has been frozen all winter. A tomato planted in 50°F soil will sit there for weeks, roots barely growing, while a tomato planted in 65°F soil will take off when ready.

If your last frost date arrives but soil is still below 60°F, wait. Waiting one to two weeks for soil to warm is not lost time — it is gained time, because the plant will grow faster in warm soil than it would have in cold soil planted early. You can speed soil warming by laying black plastic or landscape fabric over the bed for a week or two before planting.

Regional timing: cool climates versus warm climates

In cool climates with short growing seasons — the northern United States, Canada, and high elevations — the last frost date can be as late as June 1st. Plant as soon as soil warms after that date. Choose early-maturing varieties that produce fruit in 60 to 75 days, so you harvest before the first fall frost. In these regions, starting seeds indoors is almost essential because the outdoor season is too short to start from seed outside.

In warm climates with mild winters — the southern United States, parts of California, and the Southwest — you have two planting windows. Spring planting follows the same rule: after the last frost date and when soil is warm. But many warm-climate gardeners also plant tomatoes in late summer for a fall and winter harvest. For fall planting, sow seeds or transplant in late July or August, so plants mature as temperatures cool. This second season often produces better fruit because the plant avoids the intense heat of midsummer.

Tropical and subtropical regions with no frost can plant tomatoes year-round, but heat and humidity bring disease pressure. Many growers in these areas plant in the cooler months — October through March — to avoid fungal problems that thrive in heat and wet conditions.

Hardening off: the step most people skip

Whether you grew your transplants indoors or bought them from a nursery, hardening off is not optional. A plant that has lived under grow lights or in a greenhouse is not ready for full sun, wind, and temperature swings. Hardening off gradually exposes the plant to outdoor conditions so it toughens up and does not wilt or sunburn when planted.

Start by placing the plant outdoors in a shaded, sheltered spot for 2 to 3 hours. The next day, increase to 4 to 5 hours and move it to partial sun. Each day, add an hour and increase sun exposure. By day 7 to 10, the plant should be outside all day in full sun. Bring it indoors or to a sheltered spot at night until nighttime temperatures stay above 50°F. This process takes 7 to 10 days, but it cuts transplant shock and loss in half.

Planting depth and spacing matter as much as timing

Once soil is warm and the plant is hardened off, plant deep. Bury the stem up to the lowest set of leaves — tomatoes will root all along the buried stem, creating a stronger root system. Space plants 24 to 36 inches apart depending on variety; determinate (bush) types need less space, indeterminate (vining) types need more. Crowded plants get less air circulation and are more prone to disease.

Water well after planting, but do not fertilize yet. The transplant comes with nutrients from the nursery or seed-starting mix. Wait two to three weeks before explore fertilizer, or you will push leafy growth at the expense of flowers and fruit. Mulch around the base with 2 to 3 inches of straw or wood chips to keep soil temperature steady and reduce watering needs.

Frequently Asked Questions

What if my area does not have a clear last frost date?

Contact your local cooperative extension office — they have frost date data specific to your area and can account for microclimates. If you live in a region with variable weather, use the average last frost date as a guide but also watch the 10-day forecast. If frost is predicted after you plant, cover plants with row cloth or blankets overnight.

Can I plant tomatoes in a pot instead of the ground?

Yes. Container tomatoes follow the same timing rules — plant after the last frost date and when soil temperature is right. Use a pot at least 5 gallons for determinate varieties and 10 gallons for indeterminate types. Container soil warms faster than ground soil, so you may be able to plant a week or two earlier. Water containers more often because they dry out faster than garden beds.

What happens if I plant tomatoes too early?

The plant will sit dormant in cold soil, roots barely growing, while it waits for warmth. Diseases like damping-off and root rot are more likely in cold, wet soil. By the time soil warms, you have lost 2 to 4 weeks of growing time. Planting at the right time — even if it means waiting — produces a stronger plant and a better harvest.

How do I know if my soil is 60°F without a thermometer?

A soil thermometer is inexpensive and removes the guesswork. If you do not have one, a rough guide is to wait until nighttime temperatures stay above 50°F for a week. Soil temperature usually lags air temperature by a few days, so if nights are consistently warm, soil is likely warm enough. But a thermometer is the only way to be sure.

Can I plant tomatoes in spring and again in summer?

In warm climates, yes — plant in spring for early summer harvest, then plant again in mid-to-late summer for a fall harvest. In cool climates, a second planting in summer will not mature before frost. Stick to one spring planting in short-season areas and choose early varieties to may support fruit before the first fall frost.