Plant tomatoes outside 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 of the final frost in your area. Tomatoes die when exposed to frost. Plant too early and a late cold snap will kill them. Plant on time and they thrive. You can find your frost date by entering your zip code into the USDA Plant Hardiness Zone Map or by calling your local cooperative extension office.

Beyond the frost date, soil temperature matters as much as air temperature. Tomato seeds and seedlings grow slowly in cold soil and are prone to disease. Wait until soil reaches at least 60°F before planting, ideally 65°F or warmer. You can measure soil temperature with a soil thermometer, available at any garden center for under $15. Check the temperature in the morning, when it is most stable.

In most of the United States, this means planting between mid-April and late May. In the Deep South and coastal areas, it can be as early as late February or March. In the upper Midwest and northern states, it may not be safe until early June. The timing varies by hundreds of miles, so your local frost date is more reliable than any national calendar.

Key Takeaways

  • Find your last spring frost date by searching the USDA Plant Hardiness Zone Map with your zip code or calling your county cooperative extension.
  • Wait to plant until soil temperature is at least 60°F, measured with a soil thermometer in the morning.
  • Planting before the frost date or in cold soil causes seedlings to sicken, rot, or die when temperatures drop.
  • Hardened-off seedlings (gradually exposed to outdoor conditions) can go in the ground a few days before the frost date if soil is warm enough.
  • In warm climates, tomatoes can be planted in late winter; in cold climates, wait until early summer.

How to find your exact frost date

The USDA Plant Hardiness Zone Map is the standard tool. Go to planthardiness.ars.usda.gov, enter your zip code, and the map will show your zone and your average last spring frost date. Write this date down — you will use it every year.

If you do not have internet access or want a second opinion, call your county cooperative extension office. They have the frost data for your specific area and can tell you not just the average date but also the range — some years it comes early, some years late. They can also tell you whether your soil typically warms up quickly or slowly, which matters if you are on the edge between two planting windows.

Do not rely on when your neighbors plant or on what you planted last year. Frost dates shift slightly year to year. A neighbor in a different part of town may have different microclimatic conditions — a low-lying area stays colder longer, while a south-facing slope warms faster.

Why soil temperature matters as much as air temperature

Tomato roots cannot absorb water or nutrients efficiently in cold soil, even if the air is warm. A seedling planted in 50°F soil will sit dormant and may develop root rot before it grows. The same seedling in 65°F soil will establish roots within days and grow steadily.

Cold soil also encourages fungal diseases like damping off, which kills seedlings at the soil line. Waiting for warm soil is not being cautious — it is the difference between a plant that grows and one that fails. A soil thermometer takes the guesswork out. Push it 4 inches into the soil in the morning, wait 2 minutes, and read the temperature. If it is below 60°F, wait another week and check again.

Hardening off seedlings before planting

Hardening off means gradually exposing indoor-grown seedlings to outdoor sun, wind, and temperature swings over 7 to 10 days. A seedling grown indoors under lights is tender. Moved directly outside, it will wilt, bleach, or die. Hardened-off seedlings are tougher and can tolerate the shock of transplanting.

Start hardening off about 10 days before your frost date. Place seedlings outside in a sheltered, shaded spot for 2 to 3 hours on the first day. Each day, increase the time and move them into more sun. By day 7 or 8, they should be in full sun for most of the day. By day 10, they can stay out overnight if temperatures stay above 50°F. A hardened-off seedling can go in the ground a few days before the frost date if soil is warm, because it is less fragile than an indoor plant.

Regional planting windows across the United States

Planting dates vary widely by region. The Deep South (USDA zones 8b and 9) typically plants in late February through March. The Mid-Atlantic and upper South (zones 7 and 8a) plant in mid-April through early May. The Midwest and Northeast (zones 5 and 6) plant in late April through May. The upper Midwest and northern states (zones 3 and 4) plant in late May through early June.

Coastal areas and high elevations may have shorter growing seasons and later frost dates than inland areas at the same latitude. A town 50 miles inland may be safe to plant two weeks earlier than a coastal town. Elevation matters too — every 1,000 feet of elevation adds roughly 10 days to the frost date. Check your specific zone rather than assuming based on your state.

What happens if you plant too early

Planting before the frost date is the most common mistake. A late frost will kill seedlings outright or damage them so severely they never recover. Even a light frost (32°F to 35°F) can kill tomato foliage and stunt growth. A hard freeze (below 28°F) kills the entire plant.

Cold soil also causes seedlings to yellow, wilt, and develop fungal infections. They may survive but grow so slowly that they never catch up to plants started at the right time. A plant that should flower in 6 weeks may not flower for 10 weeks if it spent its first month in cold soil. You lose time and harvest.

If frost is forecast after you have planted, cover seedlings with row covers, blankets, or cloches overnight. Remove the cover in the morning when temperatures rise. This can buy you a few days if you planted slightly early and a surprise frost arrives.

Starting seeds indoors versus buying seedlings

If you start seeds indoors, sow them 6 to 8 weeks before your frost date. This gives seedlings time to grow large enough to transplant. A seedling should be 6 to 8 inches tall with at least two sets of true leaves before it goes outside. If you buy seedlings from a nursery, they are usually ready to plant when ready, so buy them a week or two before your frost date.

Nursery seedlings are often hardened off already, since they have been outside in the greenhouse. Home-grown seedlings need the full hardening-off process. Either way, do not rush. A seedling planted at the right time in warm soil will outgrow one planted early in cold soil by mid-summer.

Frequently Asked Questions

Can I plant tomatoes if the air is warm but the soil is still cold?

No. Warm air does not warm soil quickly. Tomato roots will not grow in cold soil, and the seedling will sit dormant or rot. Wait for soil temperature to reach 60°F, even if the air is 70°F or warmer. Soil warms slowly in spring, especially if it is wet or shaded.

What if my frost date has already passed but my seedlings are not ready?

Plant them anyway, as long as soil is warm. The frost date is an average, not a may provide. Some years the last frost comes early, some years late. If soil temperature is 65°F or higher and your seedlings are hardened off, they will be fine. If frost is forecast, cover them overnight.

Do I need to wait longer in a shaded garden?

Yes. Shaded soil warms more slowly than sunny soil. If your garden is shaded in spring but sunny by summer, wait an extra week or two. You can also warm soil faster by laying black plastic or landscape fabric over the bed for a week or two before planting.

Can I plant cherry tomatoes earlier than large tomatoes?

No. All tomato varieties have the same temperature requirements. Cherry tomatoes are not more cold-hardy than beefsteaks. Plant all varieties after the frost date and when soil is warm.

What if I plant in containers instead of the ground?

Container soil warms faster than ground soil, so you can plant a week or two earlier. Fill containers with potting mix (not garden soil) and place them in full sun. Check soil temperature the same way — it should be 60°F or warmer. Containers also dry out faster, so water more often once plants are growing.