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

The single most important date for outdoor tomatoes is your last frost date — the average date of the final freeze in your area. Tomatoes planted before this date will die if frost returns. You can find your last frost date by entering your zip code into the USDA Hardiness Zone map or by calling your local cooperative extension office.

Soil temperature matters as much as air temperature. Tomato seeds and transplants sit dormant or rot in cold soil. Wait until soil reaches at least 60°F before planting seeds directly in the ground, and 65°F or warmer if you are transplanting seedlings you started indoors. A soil thermometer costs five to ten dollars and removes the guesswork.

In most of the continental United States, this means planting between mid-April and late May. In the Deep South and southern California, you may plant in March. In northern states and at high elevation, you may not plant until June. The exact window depends entirely on where you live.

Key Takeaways

  • Your last frost date is the cutoff — tomatoes planted before it will freeze, so check your USDA zone or call your extension office to find yours.
  • Soil temperature is as important as air temperature; wait for soil to reach 60°F for seeds or 65°F for transplants, measured with a soil thermometer.
  • Most gardeners in the continental U.S. plant between mid-April and late May, but this shifts earlier in warm regions and later in cold ones.
  • Hardening off indoor seedlings for 7 to 10 days before planting prevents transplant shock and improves survival rates.
  • Planting too early is the most common mistake; a few weeks of delay beats losing plants to frost or watching them sit stunted in cold soil.

How to Find Your Last Frost Date

The USDA Hardiness Zone map is the standard reference. Go to planthardiness.ars.usda.gov, enter your zip code, and the map will show your zone and your average last frost date. Write this date down — you will use it every spring.

Your local cooperative extension office has the same information and can answer follow-up questions about your specific microclimate. If you live in a valley, on a hilltop, or near a large body of water, your actual frost date may differ from the county average. Extension offices know these local patterns. Find yours by searching "[your state] cooperative extension" plus your county name.

Gardeners in your area often know the practical date — the one when frost actually stops, not just the statistical average. Talking to neighbors or a local garden center gives you a sense of how conservative or aggressive to be. Some gardeners plant a week or two before the official date and accept the risk; others wait a week or two after and lose nothing.

Soil Temperature and Why It Matters More Than You Think

Tomato seeds need soil at least 60°F to germinate. Below that, they sit in the ground for weeks without sprouting, and they rot more easily. Transplants planted into cold soil do not die when ready, but they stall — they stop growing, turn pale, and become vulnerable to disease. A transplant planted into 55°F soil may take three weeks to resume growth; the same plant in 70°F soil takes three days.

Measure soil temperature in the morning, in the spot where you plan to plant, at a depth of four inches. A soil thermometer is inexpensive and accurate. If you do not have one, wait until nighttime temperatures stay above 50°F for at least a week — that is a rough signal that soil has warmed enough.

Soil warms faster in raised beds and containers than in ground beds, and faster in dark soil than light soil. If you are impatient, these tricks shorten the wait by a week or two. Black landscape fabric or black plastic laid over the bed for two weeks before planting also traps heat and warms the soil faster.

Regional Planting Windows Across the United States

Timing varies dramatically by region. The Deep South (southern Louisiana, southern Texas, southern Florida) can plant in late February or early March and often plants a second crop in late summer. The mid-Atlantic and upper South (Virginia, North Carolina, Tennessee) typically plant in mid-April to early May. The Midwest and Northeast plant in late April to late May. The Pacific Northwest and high-elevation areas plant in late May or early June.

If you live in a warm climate with two growing seasons, you have a second window in late summer for a fall crop. This crop matures in cooler weather and often produces sweeter fruit. Plant the second crop 10 to 12 weeks before your first expected frost in fall.

Microclimates within regions matter. A south-facing slope warms weeks earlier than a north-facing one. A garden next to a building or paved surface warms faster than one in open ground. If you have grown tomatoes in your yard before, you know whether your spot is early or late compared to the county average.

Hardening Off Seedlings Before Planting

If you started tomato seedlings indoors under lights, they are soft — adapted to still air, consistent warmth, and no direct sun. Planting them straight outside causes transplant shock: leaves wilt, growth stops, and some plants die. Hardening off means gradually exposing seedlings to outdoor conditions over 7 to 10 days.

Start by placing seedlings in a sheltered spot outdoors for an hour or two on the first day. Each day, increase the time and expose them to more wind and direct sun. By day 7 or 10, they spend the full day outside. Bring them in at night until nighttime temperatures stay above 50°F. This process toughens the leaves and stems so they survive transplanting.

Seedlings that skip hardening off often survive but grow slowly for weeks. Those that are hardened off take off within days. The extra week of preparation pays for itself in faster growth and fewer losses.

What Happens If You Plant Too Early

Planting before the last frost date is a gamble. If frost returns after you plant, seedlings die. Even if frost does not return, cold soil slows growth so much that you lose weeks of production. A tomato planted in 55°F soil in early April may not catch up to one planted in 65°F soil in late April, even though the early planting happened three weeks sooner.

The other risk is disease. Cold, wet soil encourages root rot and damping-off fungus. Seedlings planted too early sit in cold, damp conditions longer and are more likely to succumb. Waiting for warmth is not just about growth — it is about survival.

If you are eager to get your free guide, start seeds indoors 6 to 8 weeks before your last frost date. This lets you grow healthy transplants under controlled conditions while you wait for outdoor soil to warm. You plant the transplants outside at the right time, not the seeds.

Frequently Asked Questions

Can I plant tomatoes if the air is warm but soil is still cold?

No. A warm day does not mean warm soil. Soil takes longer to warm than air. A 75°F day with 55°F soil will stunt your transplants. Check soil temperature with a thermometer before planting, regardless of what the air temperature is doing.

What if I plant and frost is forecast after I already put them in?

Cover plants with blankets, cardboard, or frost cloth the night before frost arrives. Remove the cover the next morning when temperatures rise. This buys you a few degrees and can save young plants. Water the soil before covering — moist soil holds heat better than dry soil.

Is it ever too late to plant tomatoes?

Yes. Tomatoes need 60 to 85 days from transplant to first ripe fruit, depending on variety. If you plant after your first fall frost date minus 85 days, the plant will not mature before cold weather arrives. In most regions, mid-July is the cutoff for a fall crop.

Do I need to wait for nighttime temperatures to stay warm, or just the last frost date?

The last frost date is the main threshold. After that date, frost will not return. But if nighttime temperatures drop into the 40s, growth slows. Waiting until nighttime lows stay above 50°F gives you faster growth, though it is not strictly necessary for survival.

Can I plant in containers earlier than in the ground?

Yes, slightly. Container soil warms faster than ground soil because it is exposed on all sides and often sits on a warm surface. You can plant in containers a week or two before ground beds, but still wait until soil temperature reaches 60°F.