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

The single most important date for outdoor tomato planting is your area's last spring frost date. A frost will kill tomato seedlings, so you cannot plant outside until that date has passed. You can find your last frost date by entering your zip code at almanac.com/gardening/frostdates or asking your local cooperative extension office.

Even after the frost date passes, soil temperature matters more than air temperature. Tomato roots will not grow in cold soil, and seeds or transplants planted too early will sit dormant or rot. Wait until soil temperature reaches at least 60°F, ideally 65°F or higher. You can measure soil temperature with a soil thermometer, available at any garden center for under $15.

Nighttime air temperature should stay above 50°F consistently. If nighttime temperatures are still dipping below 50°F after your frost date, wait another week or two. Tomatoes planted into cold nights will stall, yellow, and become vulnerable to disease.

Key Takeaways

  • Your last spring frost date is the earliest you can safely plant tomatoes outside; find it by zip code at almanac.com or contact your local extension office.
  • Soil temperature must reach 60°F or higher before planting, which typically occurs one to three weeks after the frost date depending on your region.
  • Nighttime air temperatures should stay above 50°F consistently; planting into cold nights causes stunted growth and disease problems.
  • In most of the United States, outdoor tomato planting happens between mid-April and late May, but timing varies significantly by location.
  • Hardening off seedlings for seven to ten days before planting reduces transplant shock and helps plants adjust to outdoor conditions.

How to find your last frost date

Your last frost date is the average date of the final spring freeze in your area. It is not a may provide—frost can occur after this date—but it marks the point when frost becomes unlikely enough to plant frost-sensitive crops like tomatoes.

The fastest way to find it is the USDA's frost date tool at almanac.com/gardening/frostdates. Enter your zip code and the tool returns your last spring frost date. If you prefer to speak with someone, call your county's cooperative extension office. They maintain local frost data and can tell you the date in one call. You can find your extension office at nifa.usda.gov/about/offices/state-regional-offices.

Last frost dates range from February in southern Florida to June in parts of Montana and Alaska. The continental United States clusters around mid-April to mid-May, but do not assume your neighbor's date applies to you—elevation, proximity to water, and local geography shift the date by weeks.

Soil temperature: the real limiting factor

Tomato seeds and transplants will not root in cold soil. Below 60°F, roots sit dormant. Below 50°F, they may rot before they grow. Even if air temperature is warm and the frost date has passed, cold soil will stall your plants for weeks or cause them to fail entirely.

Measure soil temperature with a soil thermometer pushed 4 inches into the ground in the morning. Take the reading in the spot where you plan to plant. If it reads below 60°F, wait. Soil typically warms 5 to 10 degrees between the frost date and three weeks later, depending on how much sun your garden receives and whether you have mulched or covered the bed.

If you are impatient, you can warm soil faster by laying black plastic or landscape fabric over the bed for one to two weeks before planting. This traps solar heat and can raise soil temperature by 5 to 8 degrees. Remove the covering before planting and water the soil thoroughly.

Nighttime temperature and transplant hardening

Tomato seedlings grown indoors are tender. They have never experienced wind, direct sun, or temperature swings. Planting them straight into the garden stresses them severely, and cold nights make that stress worse. Nighttime temperatures below 50°F will cause leaves to yellow, growth to stall, and the plant to become vulnerable to fungal disease.

Before planting, spend seven to ten days hardening off your seedlings. This means gradually exposing them to outdoor conditions. Start by placing them in a sheltered spot outdoors for two to three hours on the first day, then bring them inside. Each day, increase the time outside and reduce shelter (move them from shade to dappled sun to full sun). By day seven or ten, they can stay outside overnight if nighttime temperature stays above 50°F.

If a cold night is forecast while you are hardening off, bring the seedlings back inside. One hard frost will kill them. Hardening off takes time, but it cuts transplant failure in half and produces stronger plants that grow faster once planted.

Regional planting windows across the United States

Planting dates vary widely by region. The South and Southwest can plant in late March or early April. The Midwest and Mid-Atlantic plant in mid-April to early May. The Northeast and upper Midwest plant in late May. The Pacific Northwest plants in late April to mid-May. Alaska and high-elevation areas plant in June.

These are rough ranges. A specific date depends on your exact location, elevation, and microclimate. A valley floor warms faster than a hilltop. A spot next to a south-facing wall warms faster than an open field. Use your last frost date and soil temperature as your guides, not a calendar date.

If you live in a warm climate where frost does not occur, you can plant tomatoes in late winter or early spring when soil temperature reaches 60°F. In tropical areas, tomato planting often happens in fall or early winter to avoid the hottest months.

What happens if you plant too early

Planting tomatoes before soil reaches 60°F or before nighttime temperatures stay above 50°F causes several problems. The plant sits in the ground without growing roots, making it vulnerable to rot and disease. Leaves yellow and curl. Growth stalls for weeks, and by the time soil warms, the plant is weak and behind schedule.

Early-planted tomatoes also produce fewer flowers and fruit because they have spent energy surviving cold stress instead of growing. You lose weeks of growing season and end up with smaller harvests. Waiting two to three weeks for proper conditions produces stronger plants, faster growth, and more fruit by fall.

The only exception is if you are planting in a warm climate where frost does not occur and soil is already warm. In that case, plant as soon as soil temperature reaches 60°F.

Protecting young plants from unexpected cold

Even after you plant, a surprise cold snap can damage or kill young tomato plants. If frost is forecast within a week of planting, cover the plants with row covers, blankets, or cloches (plastic domes). Remove the cover during the day if temperature rises above 50°F so the plant can photosynthesize.

If a hard frost occurs after planting and kills the foliage, the plant may regrow from the roots if the roots survived. Wait a week before pulling the plant out. If new growth appears, leave it and let it recover. If nothing grows, replant.

Once plants are 12 inches tall and nighttime temperatures consistently stay above 55°F, frost risk is nearly gone and you can stop worrying about cold damage.

Frequently Asked Questions

Can I plant tomatoes if the frost date has passed but soil is still cold?

No. Soil temperature matters more than the frost date. A frost date only tells you when frost becomes unlikely. If soil is below 60°F, roots will not grow and the plant will rot or sit dormant. Wait for soil to warm, even if that means planting a week or two after the frost date.

What if I plant too early and the seedlings turn yellow?

Yellow leaves mean the plant is stressed by cold. Stop watering as much (cold, wet soil makes it worse), and wait for soil and air to warm. The plant may recover once conditions improve, but it will be weeks behind. Next year, wait for proper conditions before planting.

Do I need to harden off seedlings if I buy transplants from a nursery?

Yes. Nursery seedlings are also grown indoors under lights and need the same gradual exposure to outdoor conditions. Hardening off takes seven to ten days but prevents transplant shock and failure. Skip it and you risk losing the plant or stunting its growth for weeks.

Can I plant tomatoes in containers earlier than in the ground?

Slightly earlier, because you can control soil temperature by using warm potting mix and placing containers in a sunny spot. But the same rules explore: soil should be 60°F and nighttime air above 50°F. Containers warm faster than ground soil, so you may gain a week or two, but not much more.

What if I live somewhere without a clear frost date?

If you live in a warm climate where frost does not occur, plant when soil temperature reaches 60°F and stays there. If you live in a very cold climate with a very late frost date, start seedlings indoors eight to ten weeks before the frost date, then plant outside after hardening off. Your local extension office can give you specific timing for your area.