Plant tomatoes outside after the last frost date in your area, when soil temperature reaches 60°F and ideally 65°F or warmer

The single most important rule is this: tomatoes cannot survive frost. A hard freeze will kill the plant, so planting before your area's last frost date is the fastest way to lose your seedlings. The last frost date is the average date of the final frost in spring for your specific location — not a guess, but a number your local cooperative extension office has calculated from decades of weather records.

Beyond frost safety, soil temperature matters as much as air temperature. Tomato seeds and transplants sit dormant or grow very slowly in cold soil, even if daytime air feels warm. Soil that is 50°F or colder will rot seeds before they sprout. Transplants (the seedlings you buy or grow indoors) will sit stunted for weeks. At 60°F, growth begins. At 65°F or higher, tomatoes grow steadily and establish roots fast enough to handle transplant shock.

Most gardeners plant tomatoes 1 to 2 weeks after the last frost date, once soil has warmed. This timing gives you a safety margin — a late frost won't catch you — and warm enough soil that the plant establishes quickly instead of languishing.

Key Takeaways

  • Find your last frost date through your local cooperative extension office or by entering your zip code into the USDA Hardiness Zone map; this date is the foundation of your planting timeline.
  • Check soil temperature with a soil thermometer before planting; tomatoes need soil at least 60°F, ideally 65°F or warmer, regardless of air temperature.
  • Plant transplants (seedlings) 1 to 2 weeks after your last frost date to allow soil time to warm and give yourself a frost safety margin.
  • Hardening off — gradually exposing indoor seedlings to outdoor sun and wind over 7 to 10 days — prevents transplant shock and sunscald when you move them outside.

How to Find Your Last Frost Date

Your last frost date is not a guess. The USDA Hardiness Zone map and your local cooperative extension office both have this number for your exact location. Enter your zip code into the USDA map at planthardiness.ars.usda.gov, and it will show your zone and frost dates. Alternatively, search "[your county] cooperative extension" and call or visit their website — they maintain frost date records specific to your area and can tell you the date in one conversation.

Frost dates vary by elevation and proximity to water. A town 20 miles away may have a different date than yours. Using your actual location's date, not a neighboring county's, prevents planting too early and losing plants to a late freeze.

Checking Soil Temperature Before You Plant

Air temperature and soil temperature are not the same. A day with 70°F air can have 50°F soil, especially early in spring. Tomatoes respond to soil temperature, not air temperature, so checking it is not optional if you want the plant to grow instead of rot or stall.

Buy a soil thermometer (they cost $8 to $15 at garden centers and online retailers) and push it 4 inches into the soil where you plan to plant. Take the reading in the morning, when soil is coolest. If it reads below 60°F, wait a week and check again. Once it reaches 60°F consistently, you can plant. Waiting for 65°F or higher gives faster, more vigorous growth.

If you are planting in containers or raised beds, these warm faster than in-ground soil because they absorb more sun. Check the temperature in the container itself, not the surrounding ground.

Hardening Off Seedlings Before Moving Them Outside

Seedlings grown indoors under lights are tender. Moving them directly from a warm, still, sheltered environment to full sun and wind causes transplant shock — wilting, leaf burn, and sometimes death. Hardening off is the process of gradually exposing them to outdoor conditions over 7 to 10 days so they toughen up.

Start 10 days before your planting date. On day 1, place seedlings in a shaded, sheltered spot outdoors for 2 to 3 hours. Each day, increase the time outside and move them into more direct sun. By day 7 or 8, they should spend the full day outside. By day 10, they can stay out overnight if temperatures stay above 50°F. Then transplant them into the garden.

If you skip hardening off and plant tender seedlings directly in full sun, they often wilt severely or develop sunscald — pale, papery patches on leaves and fruit. Hardening off takes time but prevents weeks of recovery or plant loss.

Regional Planting Timelines

Planting dates shift across the country because frost dates shift. In the Deep South (zones 8 and 9), the last frost date falls in mid-March to early April, so tomatoes go in the ground in late March or early April. In the upper Midwest and Northeast (zones 4 and 5), the last frost date is mid-May to late May, so planting happens in early to mid-June. In the Pacific Northwest, frost dates vary widely by elevation and distance from the coast, so checking your specific location is essential.

If you live in a very hot climate (zone 10 or higher), you may plant tomatoes in fall instead of spring, because summer heat stops flowering and fruit set. Ask your local extension office whether spring or fall planting makes sense for your area.

What Happens If You Plant Too Early

Planting before the last frost date risks a hard freeze killing the plant outright. Even if frost does not kill it, cold soil slows growth so much that the plant sits stunted for weeks, and cold-stressed plants are more vulnerable to disease and pests. You lose time and often lose the plant.

Planting in soil colder than 60°F causes seeds to rot before sprouting and transplants to sit motionless for weeks. The plant does not grow; it waits. By the time soil warms, you have lost 2 to 4 weeks of the growing season, and your harvest comes later or not at all.

What Happens If You Plant Too Late

Planting too late shortens the growing season. Tomatoes need 60 to 85 days from transplant to first ripe fruit, depending on variety. If you plant in mid-July in a zone where the first fall frost arrives in mid-September, you have only 60 days — enough for some varieties, but not for large slicers. Late-planted tomatoes often produce green fruit that never ripens before frost.

There is no harm in planting a few weeks after the optimal window, as long as you choose a variety bred for your season length. Check the seed packet or plant label for "days to maturity" and count backward from your first fall frost date to see if the variety will finish in time.

Frequently Asked Questions

Can I plant tomatoes before the last frost date if I cover them with plastic or cloth?

Row covers and plastic sheeting offer some frost protection, but they are not reliable for a hard freeze. If temperatures drop below 28°F, even covered plants usually die. It is safer to wait until after the last frost date and skip the covers. If you do cover plants, remove the cover during the day so heat does not build up and damage the plant.

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

Wait for the soil to warm. Air temperature is misleading in spring — a warm day does not mean the soil has warmed. Use a soil thermometer to check. If soil is below 60°F, the plant will not grow well no matter how warm the air feels. Waiting a week or two for soil to catch up prevents weeks of stalled growth later.

Can I plant tomatoes in containers earlier than in-ground beds?

Yes, containers warm faster because they absorb more sun and have less thermal mass than the ground. Check the soil temperature in the container itself. Once it reaches 60°F, you can plant. This often happens 1 to 2 weeks before in-ground soil warms, so containers can give you an earlier start.

Does the tomato variety affect when I should plant?

All tomatoes need the same frost and soil temperature conditions to survive and grow. However, the variety affects whether it will finish ripening before your first fall frost. Early varieties mature in 55 to 70 days; main-season varieties take 70 to 85 days. If your growing season is short, choose an early variety and plant as soon as conditions allow so it has time to mature.

What if I miss the planting window and it is already June?

You can still plant, but choose an early-maturing variety (55 to 70 days) and count forward to your first fall frost date. If you have at least 60 days before frost, you have a chance at a harvest. If frost comes sooner, you will likely harvest mostly green fruit. In very hot climates, late spring planting may be too late — ask your extension office whether fall planting is an option instead.