Plant tomatoes after your last frost date, when soil temperature reaches 60°F and ideally 65°F or warmer

The single most important date for tomato planting is your last spring frost date. Tomatoes are killed by frost—even a light freeze will blacken the leaves and stop growth. Planting before this date wastes seedlings. Your local cooperative extension office or a quick search for "last frost date [your city]" will give you the exact date for your area, which varies by several weeks depending on where you live.

Beyond frost safety, soil temperature matters as much as air temperature. Tomato seeds and transplants sit dormant or rot in cold soil. Wait until soil reaches at least 60°F; 65°F or warmer is better for faster growth. You can measure soil temperature with an inexpensive soil thermometer pushed 4 inches into the ground in the morning. If you plant into soil colder than 60°F, the roots won't take up water or nutrients, and the plant will yellow and stall for weeks.

In most of the United States, this means planting between mid-April and late May. In the South and Southwest, planting may happen in March or early April. In northern regions and at high elevation, it may not be safe until June. The timing is regional, not calendar-based.

Key Takeaways

  • Never plant tomatoes before your last spring frost date, which you can find from your local cooperative extension or by searching online for your city.
  • Soil temperature must be at least 60°F, ideally 65°F or warmer, which you can check with a soil thermometer.
  • Starting seeds indoors 6 to 8 weeks before your last frost date lets you transplant larger, stronger plants once soil warms.
  • Planting too early into cold soil causes root rot and stunts growth for weeks; waiting one more week for warmth saves time overall.
  • In hot climates, you may plant a second crop in late summer for a fall harvest, timing it so fruit matures before the first fall frost.

Starting seeds indoors versus buying transplants

If you start seeds indoors, begin 6 to 8 weeks before your last frost date. This gives seedlings time to grow sturdy stems and true leaves before transplanting outside. Sow seeds into seed-starting mix (not garden soil) in a warm spot—70°F to 75°F is ideal for germination. Keep the soil moist but not waterlogged. Seedlings will sprout in 5 to 10 days and need bright light when ready, either from a south-facing window or grow lights placed 2 to 3 inches above the leaves.

If you buy transplants from a nursery or garden center, you skip the indoor step and plant them directly into the garden once soil warms. Transplants are usually ready to plant 4 to 6 weeks after your last frost date, when they have several sets of true leaves and are 6 to 8 inches tall. This is simpler for beginners and saves space indoors, but you have less control over variety and plant health.

Either way, harden off seedlings before planting them outside. Set them in a sheltered spot outdoors for a few hours on day one, then gradually increase outdoor time over 7 to 10 days. This acclimates them to wind, direct sun, and temperature swings so they don't wilt or sunburn when planted.

Soil temperature and air temperature are not the same

Air temperature and soil temperature can differ by 10°F or more. A warm day with 75°F air may have soil still at 55°F, especially if the ground was cold and wet all spring. Tomatoes respond to soil temperature, not air temperature. Cold soil slows root growth, and roots cannot absorb water and nutrients efficiently, so the plant sits stunted even if the air feels warm.

To raise soil temperature faster, lay black plastic mulch or landscape fabric over the bed a week or two before planting. This traps solar heat and warms the soil several degrees. Remove it once plants are in the ground, or cut holes in it for the transplants. In cool climates, this straightforward step can mean the difference between a plant that grows steadily and one that stalls for a month.

Planting depth and spacing for strong roots

When you transplant, bury the stem deeper than it was growing in the pot—up to the first true leaves. Tomato stems can develop roots all along their length, so burying part of the stem creates a stronger root system. This is one of the few times deeper planting is actually beneficial. Dig a hole, set the transplant in at an angle if it is tall, and cover the buried stem with soil.

Space plants 24 to 36 inches apart, depending on the variety. Determinate (bush) types need less space; indeterminate (vining) types need more. Crowded plants shade each other, trap moisture, and invite disease. Good air circulation around the leaves keeps them dry and reduces fungal problems like early blight and powdery mildew.

Timing a second planting in hot climates

In regions with hot summers and mild falls—much of the South, Southwest, and California—you can plant a second crop in late summer for a fall harvest. The goal is to have fruit mature before the first fall frost. Count backward from your first fall frost date. Most tomato varieties need 60 to 85 days from transplant to first ripe fruit, depending on the variety. Plant 70 to 90 days before the first frost to give yourself a safety margin.

For example, if your first fall frost is October 15, plant the second crop around July 15 to July 20. The plants will grow through the hottest part of summer, which slows flowering, but as temperatures drop in late August and September, they will set fruit and ripen before frost. Choose heat-tolerant varieties and provide afternoon shade during the hottest weeks to prevent flower drop.

Common mistakes that delay harvest

The most common mistake is planting too early. A gardener sees a warm week in April and plants, then a frost comes and kills the seedlings. The gardener replants, losing 2 to 3 weeks. Waiting for your last frost date and warm soil costs nothing and saves time. Mark the date on your calendar and stick to it.

Another mistake is planting into cold, wet soil and then watering heavily. Cold, soggy soil invites root rot and fungal disease. If soil is still cool, wait. If you must plant, water sparingly until soil warms and the plant is actively growing. Overwatering a cold-planted tomato is a common way to lose the plant entirely.

A third mistake is planting in shade or partial shade, thinking the plant will tolerate it. Tomatoes need at least 6 to 8 hours of direct sun daily, ideally more. Shade slows growth, delays flowering, and reduces fruit production. Choose a spot that gets full sun from mid-morning through late afternoon.

Adjusting for your microclimate

Your specific location may warm or cool faster than the average for your area. South-facing slopes warm earlier. Low-lying areas that collect cold air frost later. Gardens near large bodies of water stay cooler longer in spring. If you garden in a microclimate that is consistently cooler or warmer than your town's average, adjust your planting date by a week or two based on what you observe year to year.

Keep a straightforward garden journal. Note the date you planted, the soil temperature that day, and how the plants performed. Over a few seasons, you will know whether your garden typically warms a week early or stays cold a week longer than the official last frost date. This personal data is more useful than any general guideline.

Frequently Asked Questions

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

No. Even a light frost kills tomato plants. If frost is forecast after you plant, cover the plants with blankets, row covers, or buckets on the night of the frost, then remove the covers in the morning. But it is easier to wait until frost danger has passed before planting.

What if my soil is still cold but I really want to plant?

Wait. Planting into soil colder than 60°F causes root rot and stunts growth for weeks. You lose more time than you gain. Use the waiting period to prepare the bed, add compost, and lay black plastic to warm the soil faster.

How do I know my last frost date if I just moved?

Search online for "last frost date [your city and state]" or contact your local cooperative extension office. They have frost date maps and can tell you the average date for your exact location. This is free information they provide to gardeners.

Can I plant tomatoes in containers, and does timing change?

Yes, containers work well for tomatoes. Timing does not change—wait until after your last frost date and soil (in this case, potting mix) is warm. Containers warm faster than garden beds, so you may be able to plant a few days earlier, but follow the same frost-date rule.

What if I plant too late and summer is short?

Choose early-maturing varieties that ripen in 55 to 70 days instead of 80 to 90 days. Varieties like 'Early Girl', 'Siberia', and 'Sub-Arctic' are bred for short seasons. Even if you plant late, these will produce fruit before frost.