Plant tomatoes outside after your last frost date, when soil temperature reaches 60°F and daytime air stays above 50°F

The single most important rule is this: tomatoes cannot survive frost. A single night below 32°F will kill the plant or stop it from growing. Your last frost date is the average date of the final frost in your area — find it by entering your zip code at almanac.com/gardening/frostdates or asking your local extension office. Plant tomatoes outside only after that date has passed.

Temperature matters more than calendar date. Even if your last frost date was three weeks ago, tomatoes planted in cold soil will sit dormant, rot, or grow so slowly that you lose weeks of growing season. Soil should be at least 60°F; 65°F to 70°F is better. You can check soil temperature with a soil thermometer (under $10 at any garden center) or by feeling the soil — if it feels cold to your bare hand, wait. Daytime air temperature should stay above 50°F consistently; tomatoes grow fastest when daytime highs are 70°F to 85°F.

Key Takeaways

  • Wait until after your last frost date and soil temperature reaches at least 60°F, or the plant will not grow and may rot in the ground.
  • Check your local last frost date by zip code at almanac.com/gardening/frostdates or contact your county extension office.
  • Soil temperature matters more than air temperature — use a soil thermometer or wait until soil feels warm to your hand.
  • Hardening off (gradually exposing seedlings to outdoor conditions over 7 to 10 days) prevents shock and stunted growth when you move plants outside.
  • If you plant too early and frost threatens, cover plants with blankets, row covers, or newspaper at night and remove them during the day.

How to find your last frost date

Your last frost date depends entirely on where you live. The USDA Hardiness Zone Map divides the country into regions based on average minimum winter temperatures, and your zone determines when frost typically stops. You can find your exact date in three ways: enter your zip code at almanac.com/gardening/frostdates, search "[your city] last frost date" online, or call your county cooperative extension office (search "[your county] extension" to find the phone number).

The extension office is the most reliable source because they track local frost patterns and can tell you not just the average date but also what happened in recent years. They can also tell you if your area had a late frost last year or the year before, which helps you decide whether to wait a few extra days beyond the official date. Many gardeners plant a few days after the official date as a safety margin.

Checking soil temperature before planting

Soil temperature is more important than air temperature because tomato roots cannot absorb water or nutrients from cold soil. A plant set in 50°F soil will sit in the ground for weeks without growing, even if the air is warm during the day. Buy a soil thermometer (they cost $8 to $15) and push it 4 inches into the soil in the morning, before the sun warms the surface. Take the reading in the spot where you plan to plant.

If you do not have a thermometer, feel the soil with your bare hand. Soil that feels cold or cool to the touch is not ready. Soil that feels warm (like bathwater temperature) is ready. This method is less precise but works in a pinch. If soil is still cold, wait one to two weeks and check again. Mulching the soil with black plastic or landscape fabric for two weeks before planting can warm it faster.

Hardening off seedlings before moving them outside

If you started tomato seedlings indoors under grow lights, they are soft and will be shocked by outdoor sun, wind, and temperature swings. Hardening off means gradually exposing them to outdoor conditions over 7 to 10 days so they toughen up. Start by setting seedlings outside in a shaded, sheltered spot for 2 to 3 hours on the first day. Each day, increase the time outside and move them into more direct sun.

By day 7 or 8, seedlings should be outside all day and most of the night. Bring them inside if temperatures drop below 50°F at night. On day 10, leave them outside overnight if the temperature stays above 50°F. Seedlings that skip this process often wilt, stop growing, or die when planted in the garden. The process takes time but prevents weeks of lost growth.

What to do if frost threatens after planting

If you planted tomatoes and a frost warning appears in the forecast, you can protect them. Cover plants with blankets, old sheets, row covers, or even newspaper weighted down with stones or soil. The cover traps heat radiating from the ground and keeps frost from touching the leaves. Remove the cover during the day so the plant gets sun and air. If frost actually occurs (temperatures drop to 32°F or below), the covered plant may survive; an uncovered plant will die.

This protection works only for light frost (32°F to 28°F) and only for one or two nights. If a hard freeze is forecast (below 28°F for several hours), covering will not save the plant. In that case, it is better to wait and replant after the freeze passes. Many gardeners in areas with unpredictable late frosts plant their main crop two to three weeks after the official last frost date to avoid this problem entirely.

Regional planting windows

Planting dates vary widely by region. In the Deep South (zones 8b to 9), last frost dates fall in late March or early April, so tomatoes can go outside in April. In the Upper Midwest and Northeast (zones 4 to 5), last frost dates are in mid-May, so outdoor planting happens in late May or early June. In the Pacific Northwest (zones 8 to 9), frost dates are in April or May, but cool spring soil means waiting until late May or June for warm soil.

If you live in a warm climate where frost does not occur (zones 10 and 11), you can plant tomatoes in fall or winter instead of spring, because summer heat will stress the plants and reduce fruit set. Check your zone at planthardiness.ars.usda.gov, then adjust your planting date based on soil temperature, not just the calendar.

Spacing and depth when planting outside

Plant tomatoes deep — bury the stem up to the first true leaves. Tomatoes will grow roots all along the buried stem, creating a stronger root system. Space plants 24 to 36 inches apart (determinate varieties can be closer; indeterminate varieties need more room). Dig a hole slightly larger than the root ball, set the plant in, and fill with soil. Water well after planting.

If seedlings are tall and leggy, bury them even deeper — up to the lowest set of leaves. This prevents the plant from falling over and gives it a more stable foundation. Stake or cage the plant at planting time so you do not damage roots later by driving a stake through them.

Frequently Asked Questions

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

Row covers slow frost damage but do not prevent it in a hard freeze. You can plant a week or two early if you are willing to cover plants every night until the frost risk passes, but this is labor-intensive. Most gardeners find it simpler to wait until after the last frost date and skip the nightly covers.

What if my soil is still cold in late spring?

Wait. Cold soil causes root rot and stunted growth that you cannot fix later. If your last frost date has passed but soil is still below 60°F, cover the planting area with black plastic or landscape fabric for one to two weeks to warm it faster, then plant.

Is it better to plant seedlings or seeds directly in the ground?

Seedlings (small plants started indoors) are faster and more reliable. Direct seeding tomatoes outdoors works but takes longer — seeds need warm soil (at least 70°F) and take 6 to 8 days to sprout. Most home gardeners start seeds indoors 6 to 8 weeks before the last frost date, then transplant seedlings outside after hardening off.

How do I know if my seedlings are ready to plant outside?

Seedlings are ready when they are 6 to 8 inches tall, have at least two sets of true leaves (the leaves that look like tomato leaves, not the first round seed leaves), and have been hardened off for 7 to 10 days. Seedlings that are too small will take longer to produce fruit; seedlings that are too large and leggy are harder to transplant.

Can I plant tomatoes in containers instead of the ground?

Yes. Containers warm faster than ground soil, so you can plant a week or two earlier. Use a pot at least 5 gallons for determinate varieties and 10 gallons for indeterminate varieties. Fill with potting soil (not garden soil), water well, and place in full sun. Container tomatoes need more frequent watering than ground tomatoes.