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. Tomatoes are frost-sensitive plants that will not grow in cold soil and will die if exposed to freezing temperatures. Planting too early is the most common mistake home gardeners make, and it wastes both seed and time.

Your last frost date is the average date of the final frost in your area in spring. You can find yours by entering your zip code at almanac.com/gardening/frostdates or by calling your local cooperative extension office. In the southern United States, this date may fall in February or March. In the northern states and Canada, it can be as late as May or early June.

Even after the frost date has passed, soil temperature matters more than air temperature. Tomato seeds will not germinate in soil below 60°F, and growth slows dramatically below 65°F. A soil thermometer (available at any garden center for under $15) takes the guesswork out. Push it 4 inches into the ground in the morning and check the reading. If it reads 60°F or higher for three consecutive days, you are ready to plant.

Key Takeaways

  • Wait until after your last frost date and soil temperature reaches 60°F before planting tomato seeds or transplants outdoors.
  • Find your last frost date by zip code at almanac.com/gardening/frostdates or by calling your local cooperative extension.
  • A soil thermometer is the most reliable way to know if soil is warm enough; check it 4 inches deep in the morning.
  • Starting seeds indoors 6 to 8 weeks before your last frost date gives you larger transplants to set out when conditions are right.
  • Planting too early in cold soil causes seeds to rot and transplants to sit dormant, wasting weeks of growing time.

Starting seeds indoors versus buying transplants

You have two paths: start seeds indoors under lights, or buy transplants (seedlings) from a garden center and plant them directly outside. Starting seeds indoors takes more equipment and attention but costs less and gives you more varieties to choose from. Buying transplants is faster and requires no special setup, but limits you to what your local nursery stocks.

If you start seeds indoors, sow them 6 to 8 weeks before your last frost date. Use a seed-starting mix (not garden soil), keep it moist, and provide 14 to 16 hours of light per day under grow lights or on a sunny windowsill. Seedlings are ready to move outdoors when they have their first true leaves (the second set of leaves that appear) and soil temperature outdoors has reached 60°F.

If you buy transplants, choose stocky plants with dark green leaves and no flowers yet. Leggy, tall, or flowering transplants often struggle after planting. Harden them off by setting them outside in a sheltered spot for a few hours each day for one week before planting, gradually increasing their time in direct sun. This acclimates them to outdoor conditions and prevents transplant shock.

Timing by region and climate

Planting dates vary widely depending on where you live. In warm climates like southern Florida, southern Texas, and southern California, you may plant in late winter (January or February) because frost danger ends early. In moderate climates like the mid-Atlantic and upper South, late April or early May is typical. In cool climates like the northern Midwest, Northeast, and Pacific Northwest, late May or early June is safer.

If you live in a region with a short growing season, choose early-maturing varieties that produce fruit in 60 to 75 days rather than 80 to 90 days. Varieties like 'Early Girl', 'Siberia', and 'Sub-Arctic Plenty' are bred for short seasons. Long-season varieties like 'Brandywine' and 'Mortgage Lifter' need 85 to 100 days and work best in warm climates with long summers.

What happens if you plant too early

Planting tomato seeds in soil below 60°F causes them to sit dormant or rot before germinating. Transplants planted in cold soil will not grow; they straightforward stall, turning pale and stunted, while you wait for warmth. This wastes 2 to 4 weeks of growing time. Cold soil also invites fungal diseases like damping-off, which kills seedlings at the soil line.

The temptation to plant early is strong, especially after a warm week in March or April. But a single frost after planting kills the entire crop. Soil temperature is the reliable measure; air temperature can swing 20 degrees in a single day. Trust the soil thermometer, not the calendar or the weather forecast.

Preparing soil before planting day

While you wait for soil to warm, prepare the bed. Tomatoes need well-draining soil rich in organic matter. Work 2 to 3 inches of compost or aged manure into the top 8 to 10 inches of soil. If your soil is heavy clay, add compost to improve drainage; tomatoes in waterlogged soil develop root rot and fungal diseases.

Test your soil pH if possible (your cooperative extension can do this for $10 to $20). Tomatoes prefer soil between 6.0 and 6.8 pH. If your soil is too acidic, add lime; if too alkaline, add sulfur. Follow the test results for amounts. If you cannot test, straightforward add compost, which buffers pH naturally.

Choose a location with at least 6 to 8 hours of direct sun per day. More sun means more fruit and better flavor. Avoid planting where tomatoes, peppers, or potatoes grew in the past two years, as soil-borne diseases can persist.

Spacing and depth when planting

Space transplants 24 to 36 inches apart, depending on the variety. Determinate (bush) types can be closer; indeterminate (vining) types need more room for air circulation. Bury the transplant deeper than it was growing in its pot—up to the first true leaves. Tomatoes will root along the buried stem, creating a stronger root system.

Water thoroughly after planting and keep soil consistently moist (not soggy) for the first two weeks while roots establish. Mulch around the base with 2 to 3 inches of straw or wood chips, leaving a 2-inch gap around the stem to prevent rot. Mulch keeps soil temperature stable, reduces watering needs, and prevents soil-borne diseases from splashing onto leaves.

Extending the season in cool climates

If your growing season is short, use techniques to warm soil and protect plants. Lay black plastic or landscape fabric over the bed for 2 to 3 weeks before planting to absorb heat and warm the soil faster. Plant through holes cut in the plastic, which also suppresses weeds and retains moisture.

Wall-o-water devices (plastic tubes filled with water that surround the plant) absorb heat during the day and release it at night, protecting transplants from late frosts and warming soil. They add 2 to 4 weeks to your growing season in cool climates. Row covers (lightweight fabric) also protect young plants from frost and wind while allowing light and water through.

Frequently Asked Questions

Can I plant tomatoes if there is still a chance of frost?

No. Even a light frost kills tomato plants. Wait until your last frost date has passed and soil temperature is 60°F or higher. If frost is forecast after planting, cover plants with blankets or row covers overnight and remove them in the morning.

What if my soil is still cold but the calendar says it is time to plant?

Trust the soil thermometer, not the calendar. A warm week in April does not mean soil is ready. Check soil temperature 4 inches deep for three days in a row. If it is below 60°F, wait. Planting in cold soil causes seeds to rot and transplants to stall.

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

It depends on your last frost date and how much time remains before the first fall frost. If you have at least 70 to 80 days before the first fall frost, you can still plant. Choose early-maturing varieties and buy larger transplants rather than starting from seed to save time.

Can I plant tomatoes in containers instead of the ground?

Yes. Containers warm faster than ground soil, so you can plant 1 to 2 weeks earlier. Use a pot at least 5 gallons for determinate types and 10 gallons for indeterminate types. Fill with potting mix (not garden soil), which drains well and warms quickly.

Do I need to harden off transplants I grew indoors?

Yes. Seedlings grown indoors are tender and will wilt or burn if moved directly to full sun and wind. Set them outside in shade for 2 to 3 hours on day one, gradually increasing sun and time outdoors over one week before planting.