Plant tomatoes outside after your last spring frost and when soil reaches 60°F

The safest time to plant tomatoes outside depends on two things: when frost stops happening in your area, and whether the soil is warm enough. Tomatoes die if exposed to frost, and they grow slowly or rot in cold soil. Most regions can plant tomatoes between mid-April and late May, but your exact date depends on where you live.

To find your last frost date, search "[your city] last frost date" or check the USDA Hardiness Zone Map at planthardiness.ars.usda.gov. This date is the average day of the year when frost stops. Plant tomatoes one to two weeks after that date, once soil has warmed. You can also plant when soil temperature reaches 60°F, measured 4 inches deep with a soil thermometer — though 65°F to 70°F is better for faster growth.

Key Takeaways

  • Check your local last frost date by searching your city name plus "last frost date" or using the USDA Hardiness Zone Map.
  • Wait one to two weeks after the last frost date before planting, because soil takes time to warm after frost stops.
  • Soil temperature matters as much as air temperature — use a soil thermometer to check that soil is at least 60°F, ideally 65°F or warmer.
  • Planting too early in cold soil causes root rot, slow growth, and weak plants that produce less fruit.
  • If you start seeds indoors, harden off seedlings by exposing them to outdoor conditions for a week before planting them in the ground.

How to find your last frost date

Your last frost date is the average date when frost stops in spring. It is not the same everywhere — it depends on your elevation, proximity to water, and local geography. A city 20 miles away may have a different date than yours.

The fastest way to find it is to search your city name plus "last frost date" in a search engine. Most results will show a single date. If you want the official source, go to planthardiness.ars.usda.gov, enter your zip code, and look at the map. The USDA divides the country into hardiness zones based on average minimum winter temperatures, and each zone has a corresponding last frost date.

Write down your date and add one to two weeks to it. That is your target planting window. For example, if your last frost date is May 10, plant tomatoes between May 17 and May 24.

Why soil temperature matters more than air temperature

Air temperature and soil temperature are not the same. A warm day in April can feel like planting weather, but soil 4 inches underground may still be 45°F. Tomato roots cannot absorb water or nutrients in cold soil, so the plant sits stunted and vulnerable to rot.

Buy a soil thermometer at any garden center for $10 to $20. Push it 4 inches into the ground where you plan to plant, wait 10 minutes, and read the temperature. Tomatoes germinate and grow in soil that is 60°F or warmer, but they thrive in soil that is 65°F to 70°F. If soil is below 60°F, wait another week or two and test again.

Soil warms faster in raised beds and containers than in ground beds, so if you are growing in pots, you may be able to plant a week or two earlier. Dark soil also warms faster than light soil because it absorbs more heat from the sun.

Hardening off seedlings before planting

If you started tomato seeds indoors under lights, the seedlings are used to stable indoor conditions. Moving them directly outside shocks them — they wilt, leaves turn purple, and growth stops. Hardening off means gradually exposing seedlings to outdoor sun, wind, and temperature swings over seven to ten days.

Start by placing seedlings in a shaded, sheltered spot outdoors for two to three hours. Each day, increase the time outside and move them into more direct sun. By day seven or eight, they should spend the full day outside. On the final day or two, leave them out overnight if temperatures stay above 50°F. After hardening off, seedlings are ready to plant in the ground.

If you skip hardening off and plant tender seedlings directly in full sun, they often fail to recover. The extra week of gradual adjustment prevents transplant shock and produces stronger plants.

Regional planting windows across the United States

Last frost dates vary widely by region. The South and Southwest can plant in March or early April. The Midwest and Mid-Atlantic plant in late April or early May. The North and mountain regions plant in late May or early June. Coastal areas often have later springs than inland areas at the same latitude.

Do not rely on a neighbor's planting date if they live in a different zone or elevation. A frost in late May can happen even in areas where it is rare, and it will kill unprotected tomato plants. If you plant early and frost is forecast, cover plants with blankets or row covers the night before.

What to do if frost is forecast after planting

If you have already planted tomatoes and frost is predicted, cover plants with blankets, burlap, or frost cloth before sunset. Drape the cover loosely so it does not touch the leaves, and remove it the next morning once temperatures rise above freezing. A single frost can kill young tomato plants, so protection is worth the effort.

If plants are already in the ground and frost damage occurs, cut off the damaged leaves and stems and let the plant recover. Many tomatoes survive light frost damage and produce new growth within a week or two. Severe frost that blackens the entire plant usually means replanting.

Container tomatoes and early planting

Growing tomatoes in containers lets you plant earlier because you can move pots indoors if frost threatens. Start seeds indoors, grow seedlings in pots under lights, and harden them off as usual. Once they are hardened, move pots outside even if soil temperature is still below 60°F — you can bring them in at night if frost is forecast.

Container soil warms faster than ground soil because it is exposed to sun on all sides. Use dark-colored pots to absorb more heat. Water containers in the morning so soil stays warm during the day. This method lets gardeners in cold climates plant two to three weeks earlier than those planting directly in the ground.

Frequently Asked Questions

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

Row covers and frost cloth protect plants from light frost, but they do not warm soil. Plant only when soil reaches 60°F, even with covers. Covers help if frost happens after planting, but they do not solve the problem of cold soil slowing root growth and causing rot.

What if I plant too early and soil is cold?

Cold soil causes root rot, slow growth, and weak plants that produce less fruit. If you plant in soil below 55°F, the plant may sit dormant for weeks. It is better to wait and plant in warm soil than to plant early and watch the plant struggle.

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 seven to ten days. Harden off before checking soil temperature — do both before planting.

Can I plant cherry tomatoes earlier than large slicing tomatoes?

All tomato varieties have the same soil temperature needs — 60°F minimum, 65°F to 70°F ideal. Cherry tomatoes may produce fruit slightly faster once established, but they still need warm soil to root and grow. Plant all varieties at the same time.

What happens if I plant in soil that is 55°F instead of 60°F?

Soil at 55°F is too cold for tomato roots to absorb water and nutrients efficiently. The plant grows very slowly, leaves may yellow, and roots are vulnerable to rot. Wait until soil reaches 60°F — usually just a week or two longer — to avoid these problems.