Plant tomatoes after your last frost date, when soil temperature reaches at least 60°F and ideally 65°F or warmer

The single biggest mistake is planting too early. Tomatoes are warm-season plants—they stop growing, rot, and often die if soil is cold. Planting in March in most of the United States is too early. Planting in May is usually right. The exact date depends entirely on where you live.

Your last frost date is the average date of the final frost in spring for your area. After that date, freezing temperatures are unlikely but not impossible. You can find your last frost date by entering your zip code at almanac.com/gardening/frostdates or asking your local cooperative extension office. They have the actual frost history for your region and can tell you in one conversation whether conditions are safe right now.

Soil temperature matters more than air temperature. A warm day in April does not mean the soil is warm. Soil warms slowly. You can measure it with a soil thermometer (sold at any garden center for $10 to $20) pushed 4 inches into the ground in the morning. Wait until it reads 60°F consistently for several days, or 65°F to be safer.

Key Takeaways

  • Tomatoes need soil at least 60°F, ideally 65°F or warmer—air temperature alone is not enough.
  • Plant after your last frost date, which you can find at almanac.com/gardening/frostdates using your zip code.
  • A soil thermometer costs $10 to $20 and removes the guesswork about whether the ground is warm enough.
  • Starting seeds indoors 6 to 8 weeks before your last frost date, then transplanting seedlings after that date, is the standard approach in most climates.
  • If you plant too early and a frost comes, row covers or blankets can protect seedlings, but prevention is easier than rescue.

How to know if your region is ready now

Check three things: the calendar date relative to your last frost date, the soil temperature, and the weather forecast for the next two weeks. If your last frost date is May 15 and today is May 10, wait five more days even if the soil feels warm. Frost can still come.

If your last frost date has passed but you have not measured soil temperature, do it before you plant. Stick a soil thermometer 4 inches deep in the spot where you plan to plant, wait 2 minutes, and read it. Do this in the morning when the soil is coolest. If it reads below 60°F, wait another week and check again. Soil warms about 5°F per week in spring once air temperatures stay consistently warm.

Look at the 10-day forecast. If a hard freeze is predicted after you plant, either wait or be ready to cover seedlings with blankets or row covers at night. Most gardeners find it simpler to wait.

Starting seeds indoors versus buying transplants

Many gardeners start seeds indoors 6 to 8 weeks before the last frost date. This means seeds go in soil indoors in late February or early March (depending on your region), seedlings grow under lights for 6 to 8 weeks, and then the hardened-off seedlings go in the ground after the last frost date. This gives you larger plants and more variety than buying from a garden center.

If you buy transplants from a nursery or garden center, they are usually ready to plant around the time your last frost date arrives. Do not plant them earlier just because they are available. A 4-inch tomato plant sitting in cold soil will stall, yellow, and often die. It is better to keep it in a pot in a warm spot for another week or two than to plant it too early.

Hardening off—gradually exposing indoor seedlings to outdoor conditions over 7 to 10 days—is essential before transplanting. Move seedlings outside to a sheltered spot for a few hours the first day, then gradually increase time and exposure to wind and sun. This toughens the plant so it does not wilt when planted in the garden.

Regional planting windows

Last frost dates vary widely across North America. In the warmest regions (southern Florida, southern Texas, southern California), the last frost date may be in January or February, and you can plant tomatoes in late winter. In the coldest regions (northern Minnesota, Maine, Montana), the last frost date may not arrive until late May or early June, so planting happens in June.

The Midwest (Ohio, Indiana, Illinois, Missouri) typically has last frost dates between April 20 and May 10. The Northeast (New York, Pennsylvania, Massachusetts) typically ranges from May 1 to May 20. The South (Georgia, the Carolinas, Tennessee) typically ranges from April 1 to May 1. The Pacific Northwest (Oregon, Washington) typically ranges from April 15 to May 15. These are rough ranges—your specific town can vary by a week or two from a neighboring town.

If you are not sure, contact your local cooperative extension office. They have frost data specific to your county and can tell you the exact average date for your area. Most states have a cooperative extension website where you can also search by county.

What happens if you plant too early

Cold soil slows or stops root growth. The plant sits in the ground, does not establish roots, and often develops root rot or fungal disease. Above ground, the leaves turn purple or dark red (a sign of cold stress), growth stops, and the plant may die. Even if it survives, it will be weeks behind a plant that was planted at the right time into warm soil.

Frost after planting kills seedlings outright. If temperatures drop below 32°F after you plant, tender seedlings will blacken and die. Mature plants can sometimes survive a light frost (32°F to 28°F) if you cover them, but young transplants cannot.

The lost time is real. A tomato planted in cold soil in April may not catch up to one planted in warm soil in May, even though the April planting happened three weeks earlier. Warm soil and warm air temperatures trigger the growth hormones that make tomatoes grow fast.

Protecting plants if frost threatens after planting

If you have already planted and a frost warning appears in the forecast, cover plants with blankets, row covers, or even cardboard boxes weighted down at the edges. Do this in the late afternoon before the frost arrives, and remove the cover the next morning when temperatures rise above 32°F. The cover traps heat radiating from the soil and can protect plants from a light frost.

Water plants thoroughly before covering them. Moist soil holds heat better than dry soil. If you have time, you can also set up a sprinkler to run overnight—the water freezes on the plant, and the heat released during freezing can protect the plant. This is labor-intensive and works only for light frosts, so most home gardeners prefer to wait until conditions are reliably warm.

Frequently Asked Questions

Can I plant tomatoes in April where I live?

Only if your last frost date is in April or earlier. Check your zip code at almanac.com/gardening/frostdates. If your last frost date is May 10, planting in April will likely expose seedlings to frost. If it is April 15, you can plant after that date.

What if the soil is warm but the air is still cool?

Plant tomatoes. Soil temperature is what matters for root growth. Air temperature will warm up, and the plant will grow. Cool air does not kill established plants the way cold soil does. Just make sure frost is not in the forecast.

How do I measure soil temperature without a thermometer?

You cannot accurately. A soil thermometer costs $10 to $20 and is the only reliable way. Feeling the soil with your hand is not accurate enough—soil can feel warm on the surface but be cold 4 inches down where roots grow. Buy one; it lasts for years.

Is it ever too late to plant tomatoes?

Yes, if you plant after mid-summer in most regions. Tomatoes need 60 to 85 days from planting to first fruit, depending on variety. If you plant after July 1 in the North or August 1 in the South, the first frost may arrive before fruit ripens. Check your last frost date in fall (the first frost date) and count backward.

Can I plant tomatoes in a pot earlier than in the ground?

Slightly, because you can move the pot to a warm spot and control the soil temperature better. But the same rule applies: soil needs to be 60°F or warmer. A pot in a cold garage or unheated porch will not warm faster than the ground. A pot in a sunny, sheltered spot outdoors may warm a few days earlier than the surrounding soil.