Plant tomatoes outside after your last spring frost date, when soil temperature reaches at least 60°F (ideally 65–70°F)

The single most important rule is this: tomatoes cannot survive frost. A single night below 32°F will kill the plant or stop it from growing. Your last spring frost date is the average date of the final frost in your area—not a may provide, but a reliable marker. You can find yours by entering your zip code at the National Weather Service website or asking your local cooperative extension office.

Soil temperature matters as much as air temperature. Tomatoes planted in cold soil sit dormant and rot instead of growing. A soil thermometer (available at any garden center for under $10) takes the guesswork out. Stick it 4 inches into the ground in the morning. If it reads below 60°F, wait another week or two before planting.

Most gardeners plant 1 to 2 weeks after the last frost date, once nighttime lows stay above 50°F consistently. This gives the soil time to warm and reduces the risk of a late cold snap killing your seedlings.

Key Takeaways

  • Find your last spring frost date by zip code at the National Weather Service website or contact your local cooperative extension.
  • Wait until soil temperature reaches 60°F or higher, measured 4 inches deep with a soil thermometer.
  • Plant 1 to 2 weeks after your last frost date, when nighttime temperatures stay above 50°F.
  • Hardening off seedlings (gradually exposing them to outdoor conditions) for 7 to 10 days before planting reduces transplant shock.
  • In warm climates (USDA zones 9 and above), you may have a second planting window in late summer for a fall harvest.

How to find your last frost date

The National Weather Service maintains frost date data for every county in the United States. Go to weather.gov, enter your zip code, and look for "Freeze/Frost Information" or "Climate Data" in the local forecast section. The date listed is the statistical average—meaning there is a 50 percent chance of frost after that date and a 50 percent chance you are clear.

Your county cooperative extension office (run by your state's land-grant university) also has this information and can tell you what varieties grow best in your specific area. Search "[your county] cooperative extension" online to find the office nearest you.

If you live in a frost-prone area and want to plant earlier, use row covers or cloches (clear plastic domes) to protect seedlings from unexpected cold snaps. Remove them once nighttime lows stay above 50°F for a full week.

Checking soil temperature before planting

A soil thermometer is the most reliable tool. Push it 4 inches into the soil in the morning, wait 2 minutes, and read the temperature. Do this in the spot where you plan to plant—different parts of your garden warm at different rates. Soil in a raised bed warms faster than soil in the ground; soil in full sun warms faster than soil in shade.

If you do not have a thermometer, wait until you see consistent signs of soil warming: grass is growing actively, weeds are sprouting, and the soil is no longer muddy or hard when you dig. These signs usually appear 1 to 2 weeks after your last frost date in most climates.

Hardening off seedlings before transplanting

If you started tomato seeds indoors under grow lights, the seedlings are tender and will wilt or die if moved directly into outdoor sun and wind. Hardening off means gradually exposing them to outdoor conditions over 7 to 10 days.

Start by placing seedlings in a sheltered spot (against a wall, under an eave) for 2 to 3 hours on the first day. Each day, increase the time outdoors and expose them to more direct sun and wind. By day 7 or 8, they should be outside all day. Leave them outside overnight only if temperatures stay above 50°F. Bring them in if frost is forecast.

Seedlings that are hardened off will establish faster and produce fruit earlier than seedlings planted directly from an indoor setup.

Regional timing differences

In cool climates (USDA zones 5 and 6), the last frost date falls in mid-May to early June. Plant tomatoes in late May or early June once soil reaches 65°F.

In moderate climates (zones 7 and 8), the last frost date is typically mid-April to early May. You can plant in late April or May, often earlier than northern gardeners.

In warm climates (zones 9 and above), frost is rare or nonexistent. You can plant tomatoes in early spring (February to March) for a summer harvest. Many gardeners in these areas also plant a second crop in late summer (July to August) for a fall and winter harvest, since tomatoes stop setting fruit when daytime temperatures exceed 90°F consistently.

What happens if you plant too early

Planting in cold soil causes the roots to sit dormant instead of growing. The seedling may yellow, wilt, or develop root rot. Even if it survives, it will lag behind a seedling planted 2 weeks later in warm soil—the later plant often catches up and produces fruit at the same time.

A late frost after planting can kill the entire plant. Frost damage shows as blackened, wilted leaves and stems. Once frost kills the above-ground growth, the plant cannot recover.

If frost is forecast after you have planted, cover seedlings with row covers, blankets, or cloches before sunset and remove them the next morning once temperatures rise above 32°F.

Spacing and depth when planting outside

Dig a hole slightly deeper than the root ball of your seedling. Tomatoes can be planted deeper than they grew in the pot—bury the stem up to the first true leaves, and roots will form along the buried stem, creating a stronger root system. Space plants 24 to 36 inches apart (determinate varieties closer, indeterminate varieties farther) to allow air circulation and reduce disease.

Water thoroughly after planting and keep the soil consistently moist (not waterlogged) for the first 2 to 3 weeks while roots establish. Mulch around the base with 2 to 3 inches of straw or wood chips to retain moisture and regulate soil temperature.

Frequently Asked Questions

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

Yes, row covers and frost cloth can protect seedlings from light frosts (down to about 28°F). However, you still need soil temperature of at least 60°F for the roots to grow. A frost cloth protects the above-ground plant but does not warm the soil. Remove the cloth during the day if temperatures rise above 70°F to prevent overheating.

What if my area has unpredictable spring weather?

Wait until nighttime lows stay above 50°F for at least a week, even if this is after your official last frost date. Unpredictable areas often see a warm spell followed by a cold snap. Waiting an extra week or two is safer than replanting after frost damage.

Can I plant tomatoes in containers instead of the ground?

Yes, and containers warm faster than ground soil. A 5-gallon pot in full sun can reach planting temperature 1 to 2 weeks earlier than garden soil. Use potting mix (not garden soil) and water more frequently, since containers dry out faster. Follow the same frost date and soil temperature guidelines.

Is it too late to plant if I missed the spring window?

In cool climates, yes—tomatoes need 60 to 85 days to produce fruit, and planting after early June leaves little time before fall frost. In warm climates (zones 9 and above), a late-summer planting (July to August) works well for a fall harvest, since cooler temperatures in autumn are actually ideal for fruit production.

Do I need to wait for nighttime temperatures to warm, or just daytime?

Nighttime temperatures matter more. Tomatoes grow slowly when nighttime lows drop below 55°F, even if days are warm. Wait until nighttime lows stay above 50°F consistently before planting.