Plant tomatoes after your last spring frost, when soil reaches 60°F and air stays above 50°F at night

The single most important date for tomato planting is your area's last spring frost date. Tomatoes are killed by frost, so planting before that date wastes seedlings and money. You can find your frost date by searching "[your city] last frost date" or by checking the USDA Plant Hardiness Zone Map on the USDA website — enter your zip code and it will show your zone and approximate frost dates.

Beyond frost safety, tomatoes also need warm soil and air. Soil should be at least 60°F before you transplant seedlings outdoors; ideally 65°F to 70°F. Cold soil slows root growth and invites disease. Night temperatures should stay above 50°F consistently. If you plant too early and a cold snap hits, seedlings stall or die even if they survive the frost itself.

In most of the United States, this means planting between mid-April and late May, depending on where you live. Southern regions plant earlier; northern regions plant later. The exact window for your location is narrow — usually two to three weeks — so timing matters.

Key Takeaways

  • Find your last spring frost date by searching your city name plus "last frost date" or using the USDA Plant Hardiness Zone Map.
  • Wait until soil temperature reaches 60°F (ideally 65–70°F) and nighttime air temperature stays above 50°F before moving seedlings outside.
  • Planting too early in cold soil causes root rot, stunted growth, and seedling death even if frost does not kill the plants.
  • Hardening off seedlings — gradually exposing them to outdoor conditions over 7 to 10 days — prevents transplant shock and improves survival rates.
  • In warm climates (zones 9–11), you can plant a second crop in late summer for a fall harvest, but timing depends on your first frost date in autumn.

How to find your exact frost date

Your last spring frost date is the average date of the final frost in your area. It is not a may provide — frost can arrive after that date, and it can skip a year — but it is the best guide most home growers have. The USDA Plant Hardiness Zone Map is the official source. Go to planthardiness.ars.usda.gov, enter your zip code, and the map will show your zone (a letter and number like 7a or 9b) and your approximate frost dates.

If you prefer a faster search, type your city name and "last frost date" into any search engine. Most results will show a date range. Write it down. If you see different dates from different sources, use the earlier date to be safe — it is better to wait a few extra days than to lose seedlings to an unexpected frost.

You can also ask at a local garden center or cooperative extension office. Staff there know the local climate and can tell you not just the frost date but also whether late frosts are common in your area, which matters for planning.

Checking soil temperature before planting

Soil temperature is separate from air temperature and matters just as much. A warm day does not mean warm soil. Soil warms slowly in spring, especially if it is wet or shaded. You need a soil thermometer to know for sure — they cost $10 to $20 and are worth it if you plant tomatoes every year.

Push the thermometer 4 inches into the soil in the spot where you plan to plant. Take the reading in the morning, when soil is coolest. If it reads below 60°F, wait another week and check again. Soil that is too cold causes root rot, slows growth, and makes seedlings vulnerable to disease. Waiting one more week for soil to warm is faster than replanting dead seedlings.

If you do not have a thermometer, a rough guide is to wait until nighttime temperatures stay above 50°F for at least a week. That usually means soil is warm enough, though it is not as reliable as an actual reading.

Hardening off seedlings before transplanting

Seedlings started indoors are tender. Moving them straight from a warm, sheltered windowsill to outdoor sun and wind shocks them and often kills them. Hardening off — gradually exposing seedlings to outdoor conditions — prevents this. The process takes 7 to 10 days and is straightforward but necessary.

Start by placing seedlings outdoors in a sheltered, shaded spot for 2 to 3 hours on the first day. Bring them back inside. Each day, leave them out longer and move them into more sun. By day 7 or 8, they should be outside all day. By day 10, they can stay out overnight if temperatures stay above 50°F. After that, they are ready to plant in the ground.

If you skip hardening off or rush it, seedlings will wilt, leaves will turn purple or brown, and many will die. If you do it right, transplants are stronger and produce better than seedlings planted without hardening off.

Planting depth and spacing for transplants

When you plant a seedling, bury it deeper than it was growing in its pot. Tomatoes can grow roots all along their buried stem, so bury it up to the first true leaves. This creates a stronger root system. If the seedling is leggy (tall and thin), you can bury it even deeper — up to the lowest leaves — and it will develop roots along the buried stem.

Space plants 24 to 36 inches apart, depending on the variety. Determinate (bush) tomatoes can be closer; indeterminate (vining) tomatoes need more room for air flow. Crowded plants get disease more easily because leaves stay wet longer.

Water well after planting and keep soil consistently moist (not waterlogged) for the first two weeks while roots establish. A 2-inch layer of mulch around the base helps retain moisture and keeps soil temperature steady.

Timing a second crop in warm climates

If you live in a warm climate (USDA zones 9, 10, or 11), you can plant tomatoes twice a year. The first crop goes in after spring frost, as usual. The second crop is planted in late summer so it matures before your first fall frost. The timing depends on your fall frost date, which is the average date of the first frost in autumn.

Count backward from your fall frost date. Most tomato varieties need 60 to 85 days from transplant to first ripe fruit. Add 7 to 10 days for hardening off. That tells you when to start seeds indoors for the fall crop. For example, if your first fall frost is November 15, and your variety needs 75 days to mature, you would start seeds indoors around mid-July so transplants are ready by late August.

Fall crops often produce better than spring crops in warm climates because they mature as temperatures cool, which slows disease and extends the harvest. But timing is tight — if you plant too late, frost will arrive before fruit ripens.

Common mistakes that delay or kill seedlings

The most common mistake is planting too early. Gardeners see a warm day in March or April and plant seedlings, then a cold snap arrives and kills them. The seedlings looked fine, so the gardener plants again, wasting time and money. Wait for your frost date and warm soil. One week of waiting is faster than replanting.

The second mistake is skipping hardening off. Seedlings go from a warm, sheltered indoor space to outdoor sun and wind, and they wilt or die. It takes only 10 days and prevents this loss entirely.

The third mistake is planting in cold, wet soil. If soil is below 60°F or waterlogged, roots rot before they grow. Wait for soil to warm and drain. If your garden stays wet in spring, plant in raised beds or containers filled with warm potting soil instead.

Frequently Asked Questions

Can I plant tomatoes before the last frost date if I cover them?

Covers like row cloth or plastic can protect seedlings from light frost (28–32°F), but they do not work reliably for hard freezes (below 28°F). It is safer to wait for your frost date. If you do cover plants, remove the cover during the day so they do not overheat, and water before covering so soil stays moist.

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

Wait for soil to warm. Air temperature and soil temperature are different. Warm air does not warm soil quickly, especially if the soil is wet or shaded. Use a soil thermometer to check. If soil is below 60°F, planting now will slow growth and invite disease. Waiting one more week is worth it.

Can I plant tomato seeds directly in the ground instead of starting seedlings indoors?

Yes, but it delays your harvest by 6 to 8 weeks. Seeds need soil to be 70°F or warmer to germinate, and they take 7 to 10 days to sprout. Starting seeds indoors 6 to 8 weeks before your frost date lets you transplant seedlings as soon as soil warms, so you harvest earlier. Direct seeding works in warm climates where the growing season is long.

What if I miss my planting window?

If you miss spring planting, you can still plant in early summer if your growing season is long enough. Count the days from planting to your first fall frost. If you have at least 60 days, plant now. If you have fewer than 60 days, wait until next spring. In warm climates, you can plant a fall crop instead.

Do I need to wait for nighttime temperatures to stay above 50°F, or is one warm night enough?

Wait for nighttime temperatures to stay consistently above 50°F for at least a week. One warm night followed by a cold night will stall seedling growth and invite disease. Consistent warmth is what matters.