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

The single most important rule for tomato planting is this: wait until the danger of frost has passed and the soil has warmed up. Tomatoes are warm-season plants. If you plant them too early into cold soil or cold air, they will sit there and sulk—they may rot, fail to grow, or straightforward die. The exact timing depends on where you live.

Your last spring frost date is the average date when the last frost of the season occurs in your area. You can find yours by searching "last frost date" plus your zip code, or by asking your local cooperative extension office. Plant tomatoes outdoors two to three weeks after that date, once nighttime temperatures stay above 50°F and soil temperature reaches at least 60°F. A soil thermometer (available at any garden center for under $15) takes the guesswork out of this.

If you live in a warm climate where frost rarely or never occurs, you can plant tomatoes in late winter or early spring instead, aiming for harvest before the hottest part of summer arrives.

Key Takeaways

  • Plant tomatoes outdoors two to three weeks after your area's last spring frost date, when soil temperature reaches 60°F or higher.
  • Starting seeds indoors six to eight weeks before your last frost date gives you larger transplants ready to go into the ground at the right time.
  • Soil temperature matters more than air temperature—a cold-soil tomato plant will not grow even if daytime air feels warm.
  • In warm climates without frost, plant tomatoes in late winter so they mature before extreme summer heat arrives.
  • Hardening off seedlings by gradually exposing them to outdoor conditions for seven to ten days prevents transplant shock when you move them outside.

How to find your last frost date and use it

Your last frost date is not a guess—it is a historical average based on decades of weather records for your specific location. Search online for "last frost date" and your zip code, and you will get a specific date. You can also call your county's cooperative extension office (a free service run by your state's land-grant university) and they will tell you over the phone.

Once you know the date, count backward six to eight weeks if you plan to start seeds indoors, or count forward two to three weeks if you are buying transplants from a nursery. That forward count is your outdoor planting window. Do not plant before it, even if the weather feels warm for a few days. A late frost will kill young tomato plants outright.

Starting seeds indoors versus buying transplants

You have two paths: start from seed indoors, or buy seedlings from a nursery. Starting from seed indoors takes about six to eight weeks before your last frost date. You will need a seed-starting mix, small pots or seed trays, and a warm spot (a sunny windowsill works, though a grow light produces sturdier plants). Sow seeds about a quarter-inch deep, keep the soil moist, and expect sprouts in five to ten days.

Buying transplants from a nursery is faster and simpler if you do not have indoor growing space. Choose stocky, green seedlings with true leaves (the second set of leaves that look like actual tomato leaves, not the smooth seed leaves). Avoid tall, spindly plants or any with yellowing leaves or visible pests. Transplants are usually ready to plant out two to four weeks after you buy them, so time your purchase for a week or two before your planting window opens.

Hardening off seedlings before moving them outside

Whether you grew seedlings indoors or bought them, they need to adjust to outdoor conditions before planting. This process is called hardening off and takes seven to ten days. Start by placing seedlings outside in a sheltered, shaded spot for an hour or two on the first day. Each day, gradually increase their time outside and their exposure to direct sun.

By day seven or eight, seedlings should spend the full day outside. Bring them in at night if temperatures drop below 50°F. By day ten, they can stay out overnight if nighttime temperatures stay above 50°F. This gradual transition prevents the leaves from scorching and the plants from wilting when they move from the controlled indoor environment to the variable outdoor world.

Soil temperature and why it matters more than air temperature

A tomato plant in 40°F soil will not grow, even if the air temperature reaches 70°F during the day. Cold soil slows the plant's metabolism and can cause the roots to rot before they establish. This is why a soil thermometer is worth buying. Push it four inches into the soil where you plan to plant, wait a minute, and read the temperature. If it is below 60°F, wait another week or two and check again.

You can warm soil faster by laying black plastic mulch over the bed a week or two before planting. The plastic absorbs heat and raises soil temperature by several degrees. Remove it once you plant, or cut holes in it for the tomato plants to grow through.

Timing for different tomato varieties

All tomatoes follow the same frost-date rule, but determinate (bush) and indeterminate (vining) varieties mature at different speeds. Determinate tomatoes mature faster—usually 60 to 75 days from transplant to first fruit. Indeterminate tomatoes take longer, often 75 to 90 days or more, but they produce fruit all season until frost kills the plant.

If you live in a short-season climate, choose determinate or early-maturing varieties (look for days-to-maturity under 70 on the seed packet). If you have a long, warm growing season, indeterminate varieties will give you tomatoes from mid-summer through fall. Either way, the planting date stays the same—after your last frost and when soil is warm.

What to do if frost threatens after you have planted

If an unexpected late frost is forecast after you have planted tomatoes, cover the plants with row covers, blankets, or even cardboard boxes on the night of the frost. Remove the covers the next morning once temperatures rise above freezing. This straightforward step can save a crop that would otherwise be lost.

If plants are already in the ground and a frost kills the foliage, do not pull them out when ready. Wait a few days to see if new growth emerges from the stem. Tomato plants are tougher than they look and often recover from light frost damage.

Frequently Asked Questions

Can I plant tomatoes if the weather forecast shows warm days coming?

No. One or two warm days do not mean frost will not return. Frost can occur weeks after a warm spell. Plant only after your last frost date has passed and soil temperature stays at 60°F or above. The forecast for the next week is not reliable enough to override the historical frost date for your area.

What happens if I plant tomatoes too early?

Early-planted tomatoes in cold soil often rot at the roots, turn yellow, or straightforward stop growing. They may survive but will be stunted and produce less fruit than plants started at the right time. It is better to wait and plant healthy, vigorous seedlings into warm soil than to rush and lose weeks to slow growth.

Do I need to harden off store-bought transplants?

Yes. Even nursery-grown plants have been indoors or in a sheltered greenhouse. Hardening off for seven to ten days prevents transplant shock and sunscald. The extra week is worth it for stronger, healthier plants.

Can I plant tomatoes in containers instead of the ground?

Yes. Container tomatoes follow the same frost-date and soil-temperature rules. Use a pot at least 5 gallons for determinate varieties and 10 gallons for indeterminate types. Fill with quality potting soil (not garden soil), and plant after your last frost date when the soil in the pot has warmed to 60°F.

What if I miss my planting window and it is already summer?

You can still plant, but your harvest window shrinks. Tomatoes need 60 to 90 days to mature depending on variety. If you plant in mid-summer, choose early-maturing varieties and be ready to harvest before the first fall frost. In warm climates, you can plant a second crop in late summer for a fall harvest.