Plant tomatoes after your last spring frost date, when soil temperature reaches 60°F and daytime air temperature stays above 50°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 too early and a late cold snap will kill seedlings or transplants overnight. Plant at the right time and you avoid replanting, disease pressure, and wasted weeks.

Your last frost date varies by location. In the southern United States (zones 9 and 10), it may fall in late February or early March. In the upper Midwest and Northeast (zones 4 and 5), it typically falls in mid-May or later. You can find your specific date by entering your zip code into the USDA Hardiness Zone map or by calling your local county extension office.

Beyond frost date, soil and air temperature matter just as much. Tomato seeds germinate slowly in cold soil and seedlings stall or rot. Transplants planted into soil below 60°F will sit dormant for weeks. Wait until soil temperature reaches at least 60°F — ideally 65°F or warmer — and daytime air temperatures consistently stay above 50°F before moving plants outdoors.

Key Takeaways

  • Find your last spring frost date using the USDA Hardiness Zone map or your county extension office, then wait at least one week past that date before planting outdoors.
  • Soil temperature must reach 60°F (ideally 65°F or higher) before you transplant, which often happens one to three weeks after the frost date depending on your region.
  • Starting seeds indoors six to eight weeks before your frost date gives you transplant-ready seedlings without the risk of early outdoor planting.
  • Daytime air temperatures should stay above 50°F consistently; a single cold night below 40°F can stunt growth or kill young plants even after they are in the ground.

How to find your last frost date

The USDA Hardiness Zone map is the fastest way to find this date. Go to planthardiness.ars.usda.gov, enter your zip code, and the map will show your zone. Each zone has an associated last frost date range. Write down the date or bookmark the page so you have it for future seasons.

Your county extension office is another reliable source. Search "[your county] extension office" online or call the main number and ask for the last spring frost date. Extension offices often have additional local growing information — soil type, common pests, and variety recommendations for your area — that the map alone does not provide.

Online gardening forums and local garden centers can give you a rough idea, but they are less precise than official sources. A neighbor's experience is useful context, but microclimates within a zip code can shift the frost date by a week or more depending on elevation, proximity to water, or urban heat.

Starting seeds indoors versus buying transplants

If you start seeds indoors, begin six to eight weeks before your last frost date. This timing lets seedlings grow large enough to transplant outdoors right around the frost date, when conditions are safest. Seeds started too early will become leggy and root-bound while waiting for outdoor planting weather. Seeds started too late will still be tiny when frost date arrives and will take longer to produce fruit.

Buying transplants from a nursery or garden center removes the timing guesswork. Nurseries typically release tomato plants for sale in late spring, timed to your region's frost date. You can buy them a week or two before your frost date and keep them indoors or in a cold frame until soil and air warm up. This approach costs more per plant but saves space and eliminates the need for grow lights and seed-starting supplies.

Whichever route you choose, harden off seedlings or transplants before planting them outdoors. Spend seven to ten days gradually exposing plants to outdoor sun, wind, and temperature swings. Start with two hours of morning sun on day one, add afternoon sun on day three, and leave plants outside overnight by day seven. This process toughens the plant tissue and prevents sunscald and wilting when plants move permanently outdoors.

Soil temperature and how to measure it

A soil thermometer is the most reliable way to check soil temperature. Push the probe 4 inches into the ground in the spot where you plan to plant, wait 30 seconds, and read the temperature. Check it in the morning before the sun warms the surface. Soil temperature lags behind air temperature by one to three weeks in spring, so even if daytime air is warm, soil may still be too cold.

If you do not have a thermometer, wait one to three weeks after your last frost date. In most regions, this timing allows soil to warm naturally. You can also warm soil faster by laying black plastic mulch or landscape fabric over the bed for one to two weeks before planting — the dark material absorbs heat and raises soil temperature by several degrees.

Planting into cold soil is one of the most common reasons tomatoes grow slowly or develop root rot. The delay is not worth the risk. Waiting for soil to warm takes patience, but it cuts disease pressure and gives plants a strong start.

Regional timing examples

In zone 5 (parts of the Midwest and Northeast), the last frost date falls around May 15. Soil typically reaches 60°F by late May or early June. If you start seeds indoors in mid-March, transplants will be ready by late May, matching outdoor conditions perfectly. If you buy nursery transplants, they arrive in late May, and you can plant them when ready.

In zone 8 (parts of the South and mid-Atlantic), the last frost date falls around April 15. Soil reaches 60°F by early May. Starting seeds indoors in late February or early March gives you transplants ready by mid-April. Alternatively, you can direct-seed tomatoes outdoors in late April or early May, though transplants typically produce fruit faster.

In zone 9 and 10 (southern Florida, southern California, southern Texas), frost rarely occurs. The limiting factor shifts from frost to heat and day length. In these regions, tomatoes planted in late winter (January to February) grow through spring and early summer before extreme heat arrives. A second planting in late summer can produce a fall crop. Check with your local extension office for the best planting windows in your specific area.

What happens if you plant too early

Planting before the frost date risks losing your entire crop to a late freeze. Even a light frost (32°F to 35°F) kills tender seedlings and young transplants. A hard freeze (below 28°F) kills established plants. If frost is forecast after you have planted, cover plants with row covers, blankets, or cloches to trap heat and protect them. Remove covers the next morning when temperature rises.

Planting into soil below 60°F slows root development and growth. Seedlings may sit dormant for weeks, become stressed, and attract fungal diseases like damping-off. The plant may eventually recover once soil warms, but you lose weeks of growing time and increase the risk of disease. Starting over with new plants is often faster than waiting for a stunted plant to bounce back.

Hardening off and the transition outdoors

Hardening off is the process of acclimating indoor-grown seedlings to outdoor conditions. Indoor seedlings have thin leaves, weak stems, and no tolerance for wind or direct sun. Outdoor conditions are harsher — stronger light, drier air, temperature swings, and wind stress. Without hardening off, plants wilt, leaves bleach white or turn purple, and growth stops for weeks.

Begin hardening off seven to ten days before your planned planting date. Place seedlings in a sheltered spot outdoors (a porch, cold frame, or against a south-facing wall) for two hours in morning sun on day one. Each day, add an hour of exposure and gradually shift from morning sun to afternoon sun. By day seven, leave plants outside all day. By day ten, leave them outside overnight if temperatures stay above 50°F. On day eleven, plant them in the garden.

If a cold night is forecast during hardening off, bring plants indoors or cover them. One night below 40°F can set back growth by a week or more, even if the plant survives. The goal is steady, gradual exposure without shock.

Frequently Asked Questions

Can I plant tomatoes before the last frost date if I use row covers?

Row covers provide some frost protection, but they are not reliable enough to plant weeks early. They work best for a light frost (32°F to 35°F) lasting a few hours. A sustained freeze or hard frost will kill plants even under covers. Plant as close to the frost date as you can, use covers only as backup protection for unexpected late cold snaps, and remove covers during the day so plants get sun and air circulation.

What if my soil is still cold but the air temperature is warm?

Wait for soil to warm. Air temperature and soil temperature are not the same. Soil warms more slowly than air because it has more mass and less direct sun exposure. Planting into cold soil causes root rot and stunted growth even if daytime air is 70°F or higher. Use a soil thermometer to check, or wait one to three weeks after your frost date to let soil warm naturally.

Is it better to start seeds indoors or buy transplants?

Both work. Starting seeds indoors costs less per plant and gives you more variety choices, but requires grow lights, space, and attention to watering and hardening off. Buying transplants costs more upfront but saves time, space, and equipment. Choose based on your budget, available space, and how much time you want to spend. Either way, timing to your frost date and soil temperature matters more than the method.

What if I miss the planting window and it gets too hot?

In most regions, you can still plant in early summer if spring planting was delayed. Tomatoes planted in June will produce fruit later than May plantings, but they will still crop before frost arrives in fall. In very hot climates (zone 9 and 10), late spring planting may fail because heat arrives too quickly. In those regions, ask your extension office about fall planting windows instead.

Do different tomato varieties have different planting times?

All tomato varieties need the same frost date and soil temperature to survive outdoors. However, early-maturing varieties (60 to 70 days to fruit) are better for short-season regions because they finish before fall frost. Late-maturing varieties (80+ days) need longer growing seasons and work better in warm regions. Choose varieties suited to your season length, but plant them all on the same schedule based on your frost date and soil temperature.