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

The single most important date for tomato planting is your last spring frost date—the average date when freezing temperatures stop for the season in your area. Tomatoes cannot survive frost. Plant them outdoors only after that date has passed. You can find your frost date by searching "last frost date" plus your zip code, or by contacting your local cooperative extension office.

Beyond the frost date, wait until soil temperature reaches at least 60°F, ideally 65°F or warmer. Cold soil slows root growth and can rot seeds before they sprout. Use a soil thermometer (available at garden centers for $10 to $20) to check soil temperature in the morning. If you plant into soil colder than 60°F, seeds may sit dormant for weeks or fail entirely.

Tomato seedlings started indoors can go outside 6 to 8 weeks before your frost date if you harden them off—a process of gradually exposing them to outdoor conditions over 7 to 10 days. Direct seeds planted into the garden should go in after both the frost date and warm soil are confirmed.

Key Takeaways

  • Never plant tomatoes outdoors before your last spring frost date, which you can find by searching your zip code online or calling your local extension office.
  • Soil temperature must reach 60°F minimum, ideally 65°F or higher, before planting seeds or seedlings directly into the ground.
  • Seedlings started indoors 6 to 8 weeks before your frost date can be hardened off and moved outside once both the frost date passes and soil warms.
  • In warm climates with no spring frost, plant tomatoes in late winter or early spring when soil reaches the minimum temperature.
  • Planting too early into cold soil causes seeds to rot and seedlings to yellow and stall; waiting one to two weeks for soil to warm prevents this loss.

How to find your last frost date

Your last frost date depends entirely on where you live. The continental United States spans multiple climate zones, so the date ranges from mid-April in the warmest southern regions to late May or early June in northern states and high elevations.

Search online for "last frost date" and your zip code. The Almanac, the National Weather Service, and most university extension websites will return your specific date within a day or two. Write it down or set a phone reminder for two weeks before—that gives you time to prepare soil and harden off seedlings.

If you cannot find your zip code online, call your county's cooperative extension office. They maintain frost date records for your area and can also answer questions about soil temperature and local tomato varieties that perform well in your climate.

Checking soil temperature before planting

A soil thermometer is the only reliable way to know if soil is warm enough. Feeling the soil with your hand is not accurate—soil can feel warm on the surface while remaining cold 4 inches down, where seeds and roots need warmth.

Push a soil thermometer 4 inches into the ground in the morning, before the sun has warmed the surface. Wait 2 to 3 minutes for the reading to stabilize. If the thermometer shows 60°F or higher, you can plant. If it reads below 60°F, wait 5 to 7 days and check again. Soil warms gradually in spring, gaining roughly 5°F per week once the frost date passes.

Check soil temperature in the spot where you plan to plant, not in a shaded area or near a building. Sun exposure and soil type both affect how quickly soil warms. Dark mulch or black plastic laid over soil weeks before planting can speed warming by 5 to 10°F.

Starting seeds indoors versus direct planting

Indoor seed starting gives you a head start and lets you grow varieties that need a long season. Start seeds indoors 6 to 8 weeks before your last frost date. Seedlings will be ready to harden off and move outside right around the frost date, once soil has warmed.

Direct seeding—planting seeds straight into the garden—works if you live in a warm climate or have a long growing season. Wait until after your frost date and when soil reaches 65°F or warmer. Direct seeds take 5 to 10 days to sprout and another 60 to 85 days to produce fruit, depending on variety. Count backward from your first fall frost date to make sure you have enough time.

Most home gardeners in cooler climates use indoor seedlings because they produce fruit earlier and give a longer harvest window. If you buy seedlings from a garden center, harden them off for 7 to 10 days before planting them outside, even if they look mature. Seedlings grown indoors are tender and will wilt or die if moved directly into full sun and wind.

Hardening off seedlings: the 7- to 10-day process

Hardening off means gradually exposing indoor seedlings to outdoor sun, wind, and temperature swings so they toughen up before permanent planting. Skip this step and seedlings will wilt, turn purple, or die within days of being planted outside.

Start hardening off 7 to 10 days before your last frost date. On day one, place seedlings in a shaded, sheltered spot outdoors for 2 to 3 hours. Bring them back inside. On day two, leave them out for 4 to 5 hours in partial shade. Each day, increase time outdoors and gradually move them into more direct sun. By day 7 or 8, seedlings should spend the full day outside. If nighttime temperatures stay above 50°F, you can leave them out overnight.

Water seedlings more often during hardening off—outdoor air dries soil faster than indoor air. Check soil moisture every few hours on hot days. If leaves start to wilt, move seedlings back to shade and water when ready.

Regional timing: warm climates and late plantings

In southern regions with no spring frost—parts of southern California, southern Texas, southern Florida, and Hawaii—tomatoes can be planted in late winter or early spring. The limiting factor is soil temperature, not frost. Plant when soil reaches 60°F, which may be December or January in these areas.

In hot climates, tomatoes often stop flowering and setting fruit when temperatures exceed 90°F consistently. Many gardeners in the deep South plant a spring crop (February to April) and a fall crop (July to September) to avoid peak summer heat. Fall crops are planted in mid-summer when soil is hot, so germination is fast, and fruit sets as temperatures cool in autumn.

If you live in a region with a short growing season—northern New England, the upper Midwest, or high elevations—start seeds indoors by late February or early March. Use early-maturing varieties that produce fruit in 60 to 70 days rather than 80 to 90 days. Plant outside when ready after your frost date and when soil warms, because you have limited time before fall frost arrives.

Common mistakes that delay or damage tomato crops

Planting too early is the most common mistake. Gardeners see a warm day in April and plant seedlings, then frost arrives and kills them. Even if frost does not kill the plants, cold soil and air slow growth so much that late plantings catch up and overtake early ones by mid-summer. Wait for your frost date and warm soil—the two-week delay costs nothing.

Planting into cold, wet soil causes seeds to rot before sprouting. If spring is unusually cold and wet, wait an extra week or two rather than planting into mud. Soil that squeezes into a ball when you grip it is too wet. Soil that crumbles easily is ready.

Skipping the hardening-off step kills seedlings that look healthy indoors. Indoor seedlings have thin stems and tender leaves because they grew in stable, protected conditions. Moving them directly into sun and wind causes wilting, sunscald (white or brown patches on leaves), and death. Hardening off takes 7 to 10 days but prevents total loss.

Frequently Asked Questions

Can I plant tomatoes if there is still a chance of frost?

No. Even a light frost kills tomato plants. If frost is forecast after you have planted, cover plants with blankets, row covers, or cloches overnight and remove them in the morning. If you have not planted yet and frost is predicted, wait. One unexpected frost can wipe out weeks of growth.

What if my soil is still cold but my frost date has passed?

Wait for soil to warm. The frost date is one requirement; warm soil is the other. If soil is below 60°F, seeds will rot and seedlings will stall. Warm soil is more important than the calendar date. Use black plastic or dark mulch to speed soil warming by a week or two.

Can I plant tomatoes in containers earlier than in the ground?

Slightly earlier, because container soil warms faster than garden soil. But wait until after your frost date and until container soil reaches 60°F. Containers in full sun warm faster than ground soil, so you may gain a week or two, but frost will still kill the plants if they are outside.

How do I know if my seedlings are ready to plant outside?

Seedlings are ready when they are 6 to 8 inches tall, have at least two sets of true leaves (the leaves that look like tomato leaves, not the first round seed leaves), and have been hardened off for 7 to 10 days. Leggy, pale seedlings are not ready—they need more light indoors before hardening off.

What happens if I plant tomatoes too early and they survive?

They will sit still for weeks, turning purple or yellow as cold soil stresses roots. Growth stops until soil warms. A tomato planted at the right time into warm soil often catches up to and passes an early-planted tomato by July. You lose nothing by waiting, and you avoid the risk of frost damage.