Plant tomatoes outside after your last spring frost date, when soil temperature reaches 60°F and ideally stays above 50°F at night

Tomatoes are warm-season plants. They stop growing below 50°F at night and die if exposed to frost. The single most important date for outdoor planting is your last spring frost date — the average date of the year's final freeze in your area. You can find this date by entering your zip code into the USDA Hardiness Zone map at planthardiness.ars.usda.gov, or by calling your local cooperative extension office.

Even after that frost date passes, soil temperature matters as much as air temperature. Tomato roots absorb nutrients poorly in cold soil, and the plant will sit dormant rather than grow. Wait until soil reaches at least 60°F before planting; 65°F to 70°F is better. You can check soil temperature with a straightforward soil thermometer from any garden center, inserted 4 inches deep in the morning.

The timing also depends on what kind of tomato you are growing. Determinate varieties (bush types that fruit all at once) can go in the ground closer to your frost date. Indeterminate varieties (vining types that fruit all season) need more time to mature and benefit from being planted earlier if your frost date allows — but never before soil warms up.

Key Takeaways

  • Your last spring frost date is the hard important date; tomato plants will die if exposed to frost, even briefly.
  • Soil temperature must reach 60°F (ideally 65°F to 70°F) before planting, which often happens one to three weeks after the frost date passes.
  • You can find your frost date by zip code on the USDA Hardiness Zone map or by calling your county's cooperative extension office.
  • Indeterminate (vining) tomatoes need more growing time than determinate (bush) types, so plan earlier if your climate allows.
  • Hardening off seedlings — gradually exposing them to outdoor conditions over 7 to 10 days — prevents transplant shock and helps them survive the move outside.

How to find your last frost date

The USDA Hardiness Zone map (planthardiness.ars.usda.gov) is the standard tool. Enter your zip code and the map will show your zone and, in most cases, the average date of your last spring frost. This is an average, not a may provide — frost can arrive a week or two later or earlier in any given year, but the average is what gardeners use to plan.

Your county's cooperative extension office is another reliable source. They have local frost data and can often tell you the date over the phone. Search "[your county] cooperative extension" online to find the office number. Extension agents also know which tomato varieties do best in your area and when local gardeners typically plant.

If you live in a region with unpredictable spring weather, some gardeners plant a week or two after the frost date to be safe. Others use frost cloth or row covers to protect plants if an unexpected late frost is forecast. Neither approach is wrong — it depends on how much risk you want to take.

Checking soil temperature before planting

A soil thermometer costs $8 to $15 and takes the guesswork out of timing. Push it 4 inches into the soil in the morning, wait 2 to 3 minutes, and read the temperature. Do this for three or four days in a row to see the trend. Soil warms gradually, so a single warm day does not mean it is ready.

If you do not have a thermometer, a rough rule is to wait one to three weeks after your frost date passes. In cooler climates or wet springs, soil may take longer to warm. In warm climates or after a dry, sunny spell, it may warm faster. Planting too early into cold soil is the most common reason tomato seedlings sit still for weeks without growing.

Hardening off seedlings before moving them outside

If you started tomatoes indoors from seed or bought seedlings from a nursery, they need time to adjust to outdoor conditions before planting. This process is called hardening off and takes 7 to 10 days. Seedlings grown indoors are tender — they have not been exposed to wind, direct sun, or temperature swings.

Start by placing seedlings in a sheltered, shaded spot outdoors for 2 to 3 hours on the first day. Each day, increase the time outside and gradually move them into more direct sunlight. By day 7 or 8, they should be outside all day. Leave them outside overnight only after they have been in full sun for at least two days. If frost is forecast during hardening off, bring them back inside.

Seedlings that skip hardening off often wilt, stop growing, or die after planting. The extra week is worth the effort.

Regional timing examples

Timing varies widely by location. In the upper Midwest and Northeast, last frost dates typically fall between May 1 and May 31, so outdoor planting happens in late May or early June. In the mid-Atlantic and upper South, frost dates are usually April 15 to May 1, allowing planting in mid-to-late May. In the Deep South and Gulf Coast, frost dates arrive in March or early April, and planting can happen in April or even late March.

In mild climates with no hard frost (parts of California, Florida, and the Southwest), the limiting factor shifts from frost to heat. Tomatoes stop setting fruit when nighttime temperatures stay above 75°F, so in very hot regions, gardeners may plant in late winter or early spring to harvest before the heat arrives, or wait until late summer to plant a fall crop.

The best approach is to look up your specific frost date rather than relying on regional generalizations. A gardener 50 miles away may have a frost date two weeks earlier or later than yours.

What happens if you plant too early

Planting before soil warms and frost danger passes causes two problems. First, the plant sits dormant in cold soil, using energy without growing. Roots do not absorb water or nutrients efficiently below 50°F, so the seedling may yellow, wilt, or develop root rot. Second, if frost arrives after planting, the plant dies — you lose the seedling and have to start over.

Early planting does not save time. A tomato planted in warm soil two weeks later will often catch up to and overtake one planted early in cold soil, because the early-planted one spent those two weeks barely growing. Patience pays off.

Frequently Asked Questions

Can I plant tomatoes outside before the last frost date if I use a frost cloth?

Yes, frost cloth or row covers can protect plants from light frost (down to about 28°F), so you can plant a week or two early if you are willing to cover them on cold nights. Remove the cover during the day so the plant gets sun and air. This works best if you monitor the forecast closely and have the cloth ready to deploy quickly.

What if my area has an unpredictable spring and frost comes late?

Plant after your average frost date, not before it. If an unexpected frost is forecast after you have planted, cover the plants with cloth, cardboard, or even old sheets overnight. Water the soil before covering — moist soil holds heat better than dry soil. Remove the cover in the morning once temperatures rise above freezing.

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

Seedlings (transplants) are faster and more reliable for most home gardeners. Direct seeding takes longer because seeds germinate slowly in cool spring soil. If you direct seed, wait until soil is at least 60°F and all frost danger has passed. Seedlings can go in slightly earlier (once soil reaches 60°F) because they are already established.

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 smooth seed leaves), and have been hardened off for 7 to 10 days. Stocky, dark-green seedlings are healthier than tall, pale, spindly ones.

What if I plant and soil temperature drops below 50°F at night?

The plant will not die from a single cold night, but it will stop growing and may develop problems if cold persists. If temperatures are forecast to stay below 50°F for more than a few nights, cover the plants or consider waiting to plant until the cold snap passes. Once soil and air warm up, the plant will resume normal growth.