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 happening in your area. Tomatoes cannot survive frost. Plant them outdoors only after that date has passed. You can find your last frost date by searching "[your city] last frost date" or by checking the USDA Hardiness Zone Map, which lists frost dates by region.

Beyond frost safety, soil temperature matters just as much. Tomato seeds and seedlings grow slowly in cold soil and may rot before they germinate or establish roots. Wait until soil reaches at least 60°F, ideally 65°F to 70°F. You can measure soil temperature with a straightforward soil thermometer from any garden center. Cold soil is the reason tomatoes planted too early often sit stunted for weeks before suddenly taking off once the ground warms.

In most of the United States, this means planting between mid-April and late May outdoors, depending on where you live. Southern regions may plant in March; northern regions may wait until June. The exact window varies by hundreds of miles and by elevation.

Key Takeaways

  • Never plant tomatoes outdoors before your last spring frost date, which you can find by searching your city name plus "last frost date."
  • Soil temperature should be at least 60°F before you plant, measured with a soil thermometer rather than guessed.
  • Starting seeds indoors 6 to 8 weeks before your frost date lets you transplant larger, stronger seedlings once soil warms.
  • Planting too early in cold soil causes seedlings to sit dormant or rot rather than grow, wasting weeks of the growing season.

Starting seeds indoors versus direct seeding outdoors

Most home gardeners start tomato seeds indoors under lights 6 to 8 weeks before their last frost date. This gives you a head start: seedlings are already several inches tall and have true leaves by the time soil is warm enough to transplant them outside. You move them to the garden in late spring and harvest tomatoes weeks earlier than if you had waited to plant seeds directly in the ground.

Direct seeding—planting seeds straight into outdoor soil—works but delays your harvest. Tomato seeds germinate slowly in cool spring soil and take 7 to 10 days to sprout even in ideal conditions. By the time seedlings are large enough to survive outdoors, you have lost a month or more of growing time. In short seasons (northern climates, high elevation), direct seeding often means you never reach full maturity before frost returns in fall.

If you are buying seedlings from a nursery rather than starting your own seeds, the timing is simpler: buy them a week or two before your frost date, harden them off (expose them gradually to outdoor conditions over 7 to 10 days), and transplant them into the garden once frost danger has passed and soil is warm.

How to find and use your frost date

Your last spring frost date is not a single day—it is a statistical average based on 30 years of weather records. The date tells you when frost becomes unlikely, not impossible. Some years frost comes earlier, some years later. Use the date as a guide, not a may provide.

To find your frost date, visit the National Weather Service website and search for your city, or use the USDA Plant Hardiness Zone Map at planthardiness.ars.usda.gov. Enter your zip code and the map will show your zone and approximate frost dates. You can also call your local Cooperative Extension office—they have frost date data specific to your county and can answer questions about your local growing season.

Once you know the date, count backward 6 to 8 weeks to find when to start seeds indoors. If your last frost date is May 15, start seeds indoors around March 20 to April 1. Mark both dates on a calendar so you do not miss the indoor seeding window.

Adjusting for your specific location and elevation

Frost dates vary dramatically over short distances. A valley floor may have a frost date two weeks earlier than a hilltop five miles away. If you live in a mountainous area or near a large body of water, your local conditions may differ from the county average. Ask neighbors who garden, or check with your Cooperative Extension office for a frost date specific to your exact location.

Elevation changes the frost date by roughly one week per 300 feet of elevation gain. If you live at 5,000 feet instead of 4,000 feet, expect your frost date to be about a week later. This matters if you are gardening in the mountains or on a plateau.

Signs the soil is warm enough, beyond the thermometer

If you do not have a soil thermometer, watch for natural signs that soil has warmed. Grass and weeds begin growing vigorously. Soil feels warm to the touch when you dig a few inches down. Warm-season crops like beans and squash are being planted by other gardeners in your area. These are not precise, but they align roughly with the 60°F threshold tomatoes need.

Do not rely on air temperature alone. A warm spring day does not mean soil is warm. Soil heats and cools more slowly than air. A week of 70°F days may still leave soil at 50°F, especially if nights are cool or the ground was recently wet.

What happens if you plant too early

Planting tomato seedlings in soil below 60°F slows their growth dramatically. Roots do not develop well in cold soil, and the plant sits stunted for weeks. Seedlings may yellow or develop purple-tinged leaves as they struggle. In the worst case, seeds rot before sprouting or seedlings develop root rot and die.

Even if the seedling survives, you have wasted time. A seedling planted in 50°F soil in early April may not grow noticeably until late May, when soil finally warms. A seedling planted in 65°F soil in late May catches up and often surpasses it by mid-summer, because it grows steadily from day one. Patience pays off.

Hardening off seedlings before transplanting

Seedlings started indoors under lights are tender—they have never experienced wind, direct sun, or temperature swings. Transplanting them straight from a warm indoor shelf to the garden shocks them and can kill them or set them back weeks. Instead, harden them off over 7 to 10 days before planting.

Start by placing seedlings outdoors in a sheltered, shaded spot for an hour or two. Each day, increase their time outside and gradually move them into more direct sun. By day 7 or 8, they should be outside all day. If frost threatens, bring them back inside at night. By the end of the hardening period, they can handle full sun and outdoor conditions and are ready to plant in the garden.

Frequently Asked Questions

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

Row covers and frost blankets can protect plants from light frost (32°F to 35°F), but they are not reliable for hard freezes. If your forecast shows temperatures below 32°F, covers may not save the plants. It is safer to wait until frost danger has truly passed rather than gamble on covers.

What if I plant too early and frost kills my seedlings?

If frost kills seedlings you planted early, you can replant. Harden off new seedlings and plant them once soil is warm again. You will lose a few weeks, but you will still have time to grow tomatoes before fall frost arrives. Check your first frost date in fall to know how much growing time remains.

Do all tomato varieties have the same planting time?

Yes. All tomato varieties need soil above 60°F and must be planted after the last spring frost date. Some varieties mature faster than others (early varieties in 60 to 70 days, late varieties in 80+ days), so choose varieties suited to your growing season length, but the planting window is the same for all.

Is it too late to plant tomatoes in June?

In most regions, June planting still works, especially if you use fast-maturing varieties (60 to 70 days). You will harvest later in the season, but you should still get a crop before fall frost. In very short seasons (northern climates, high elevation), June planting may not leave enough time for full maturity.

Should I wait for the soil to warm before buying seedlings from the nursery?

You can buy seedlings a week or two before your frost date and keep them in a sheltered spot or indoors, then harden them off and plant them once soil warms. This lets you choose the best seedlings while they are in stock, rather than waiting and finding the nursery sold out.