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

The single most important date for outdoor tomatoes is your area's last spring frost. Tomato plants die in frost, so planting before that date wastes the plant and the money you spent on it. In most of the United States, this falls between mid-April (southern regions) and late May or early June (northern regions). You can find your exact frost date by searching "[your city] last frost date" or checking the USDA Plant Hardiness Zone Map, which lists frost dates by zip code.

Soil temperature matters as much as air temperature. Tomato roots will not grow in cold soil, and the plant will sit stunted for weeks even if the air is warm. Wait until soil reaches at least 60°F, ideally 65°F or higher. You can measure soil temperature with a straightforward soil thermometer from any garden center — stick it 4 inches into the ground in the morning. If you do not have a thermometer, a practical rule is to wait one to two weeks after your last frost date, when the soil has warmed.

Key Takeaways

  • Plant tomatoes outside only after your area's last spring frost date, which you can find by searching your city name plus "last frost date."
  • Soil temperature must reach 60°F or higher before planting, which you can check with a soil thermometer or by waiting one to two weeks after the frost date.
  • Hardening off seedlings — gradually exposing them to outdoor conditions over 7 to 10 days — prevents shock and wilting when you move them outside.
  • Tomatoes planted too early in cold soil will sit dormant and may rot, while tomatoes planted at the right time grow quickly and produce earlier in the season.

How to find your last frost date

Your last frost date is the average date of the final frost in spring for your specific location. This date shifts by geography and elevation — a town 20 miles north or 1,000 feet higher in elevation can have a frost date two to three weeks later. Do not use a neighboring state's date or a national average.

The fastest way to find it is to search "[your city] last frost date" in any search engine. Most results will show the date directly. You can also enter your zip code into the USDA Plant Hardiness Zone Map at planthardiness.ars.usda.gov, which displays your zone and typical frost dates. Local garden centers and county extension offices also keep this information on hand and can tell you the date in one phone call.

Why soil temperature matters more than air temperature

A warm day in April does not mean the soil is warm. Air temperature can swing 20 or 30 degrees from day to day in spring, but soil temperature changes slowly and stays more stable. Tomato roots will not absorb water or nutrients in soil below 60°F, so the plant cannot grow even if the air is 75°F. A tomato planted in cold soil will sit there for weeks, turning pale and weak, and may rot at the base before it ever grows.

Checking soil temperature takes two minutes. Push a soil thermometer 4 inches into the ground in the morning, wait 30 seconds, and read the number. Do this in the spot where you plan to plant. If the soil is below 60°F, wait a few days and check again. Once it hits 60°F consistently — meaning it stays there even on cool mornings — you can plant.

Hardening off seedlings before planting outside

If you started tomato seedlings indoors under lights, they have never felt wind, direct sun, or outdoor temperature swings. Moving them straight from a warm windowsill to the garden will shock them and stunt their growth or kill them. Hardening off means gradually exposing seedlings to outdoor conditions over 7 to 10 days so they toughen up.

Start by setting seedlings outside in a sheltered spot — against a wall, under an eave, or in a cold frame — for 2 to 3 hours on the first day. Each day, leave them out a bit longer and move them to a slightly more exposed location. By day 7 or 8, they should be outside all day. On day 9 or 10, leave them out overnight if temperatures stay above 50°F. After hardening off, the seedlings will have thicker stems and darker leaves and will transplant without wilting.

Regional planting windows across the United States

Frost dates vary widely by region, and so do the weeks when soil warms enough for tomatoes. The South — zones 8 and 9 — can plant in mid-April or even late March. The Mid-Atlantic and Midwest — zones 5 and 6 — plant in mid-May. The North and high elevations — zones 3 and 4 — plant in late May or early June. The Pacific Northwest, which stays cool and wet longer, often plants in late May even though frost dates come earlier.

Rather than relying on a region name, use your own frost date and soil temperature. A gardener in zone 5 who lives on a south-facing slope with dark soil may plant a week earlier than a neighbor in the same zone who gardens on a north-facing slope with clay. Your specific microclimate matters more than the zone.

What happens if you plant too early

Planting tomatoes in soil colder than 60°F slows their growth dramatically. The roots sit dormant, the plant does not absorb water or nutrients, and the leaves turn pale or purple. In very cold soil, the stem may rot at the base. Even if the plant survives, it will be weeks behind a tomato planted at the right time, and you will lose weeks of production at the end of the season.

A tomato planted in 50°F soil in early April may not start growing until late April when the soil finally warms. A tomato planted in 65°F soil in mid-May will grow when ready and often catch up or surpass the early-planted one by midsummer. The early planting cost you money and time with no benefit.

Protecting newly planted tomatoes from late frost

Even after you plant, a surprise frost can arrive. If the forecast calls for frost within a week of planting, cover the seedlings with a frost cloth, row cover, or even a sheet or blanket in the evening and remove it the next morning. A frost cloth lets light and water through while trapping heat. You can buy one at any garden center for $10 to $20 and reuse it for years.

If frost hits an unprotected seedling, the leaves will blacken and the plant may die. If only the leaves are damaged but the stem is still green, the plant may recover and grow new leaves. Either way, covering young plants for a few nights is cheap insurance against losing them.

Frequently Asked Questions

Can I plant tomatoes before the last frost date if I use a cold frame or row cover?

Yes, a cold frame or row cover can warm the soil and protect seedlings from frost, letting you plant one to three weeks earlier. However, you still need soil temperature of at least 60°F under the cover. Check the soil temperature inside the frame before planting. You will also need to monitor the cover on warm days to prevent overheating and remove it gradually as temperatures rise.

What if I plant tomatoes and then a frost comes?

Cover the plants with a frost cloth or sheet in the evening and remove it the next morning. If frost damages the leaves but the stem stays green, the plant will usually recover and grow new leaves. If the entire plant blackens, it is likely dead. In either case, covering plants for a few nights after planting is worth the effort.

Is it better to plant tomatoes early or wait until the soil is warm?

Waiting for warm soil produces faster growth and earlier harvests. A tomato planted in 65°F soil in mid-May will often produce fruit before one planted in 50°F soil in early April, even though it started later. Cold soil stunts growth for weeks, erasing any head start from early planting.

Can I plant tomatoes in containers outside before the frost date?

Container soil warms faster than ground soil because it is exposed to sun on all sides, so you can plant in containers a week or two earlier than in the ground. However, check the soil temperature inside the container before planting. Also move containers to a sheltered spot or cover them if frost is forecast, since the soil in a pot cools faster than ground soil at night.

What if my area does not have a clear last frost date?

Coastal areas and regions with mild winters sometimes lack a traditional frost date because frost is rare or unpredictable. In these areas, use soil temperature as your main guide — plant when soil reaches 65°F. You can also ask a local garden center or county extension office when most gardeners in your area plant tomatoes outdoors.