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

The single most important rule for tomato timing is this: soil temperature matters more than air temperature. Tomato seeds and seedlings will rot in cold soil, even if daytime air feels warm. Most regions can plant tomatoes safely between late April and early June, but your exact date depends on your local frost date and soil conditions.

Check your soil temperature with a straightforward soil thermometer (available at any garden center for under $10). Push it 4 inches into the ground in the morning. If it reads 60°F or above, you can plant. If it reads below 55°F, wait another week and test again. This single check prevents the most common mistake: planting too early and watching seedlings sit in cold soil for weeks without growing.

Key Takeaways

  • Tomatoes need soil temperature of at least 60°F, which typically arrives one to two weeks after your area's last spring frost date.
  • Starting seeds indoors six to eight weeks before your planting date gives you larger, stronger seedlings ready to go into the ground.
  • Hardening off seedlings—gradually exposing them to outdoor conditions over seven to ten days—prevents transplant shock and sunscald.
  • In hot climates, you can plant a second crop in mid-summer for a fall harvest, but timing depends on your first frost date in autumn.

Finding your last spring frost date

Your last spring frost date is the average date when freezing temperatures stop occurring in your area. This date varies by region—it might be April 15 in the South, May 15 in the Midwest, or June 1 in northern states. You can find your exact date by entering your zip code at almanac.com/gardening/frostdates or asking at your local cooperative extension office.

Once you know that date, count backward six to eight weeks to determine when to start seeds indoors. If your last frost is May 20, start seeds indoors around early April. If you are buying seedlings from a nursery instead of starting your own, you can wait until one to two weeks before that frost date, when local garden centers stock tomato plants.

Starting seeds indoors versus buying seedlings

Starting tomato seeds indoors gives you more variety choices and costs less per plant, but requires grow lights and a warm spot (70–75°F). Sow seeds in seed-starting mix about eight weeks before your planting date. Keep soil moist but not waterlogged, and provide 14 to 16 hours of light daily with a grow light positioned 2 to 3 inches above the seedlings.

Buying seedlings from a nursery or garden center is faster and requires no equipment. Look for stocky plants with dark green leaves and no flowers yet—flowering seedlings often struggle after transplanting. Avoid leggy, pale seedlings that have been crowded under poor light. Either way, you will need to harden off the plants before moving them outside permanently.

Hardening off seedlings before planting

Hardening off means gradually exposing seedlings to outdoor sun, wind, and temperature swings over seven to ten days. Seedlings grown indoors are tender and will wilt, sunburn, or die if moved directly into full sun. Start by placing them in a sheltered, shaded spot outdoors for two to three hours on day one. Each day, increase sun exposure and time outside by an hour or two.

By day seven or eight, seedlings should tolerate a full day in dappled shade. By day nine or ten, they can handle several hours of direct morning sun. If temperatures drop below 50°F at night during this period, bring plants back inside. Once nighttime temperatures stay above 50°F consistently and soil reaches 60°F, plants are ready for the garden.

Planting depth and spacing in the garden

Bury tomato seedlings deeper than they grew in their pots—up to the first true leaves. Tomatoes will develop roots all along the buried stem, creating a stronger root system. Space plants 24 to 36 inches apart depending on variety (determinate types need less space; indeterminate types need more). Rows should be 3 to 4 feet apart to allow air circulation and room to harvest.

At planting time, add a handful of compost or balanced fertilizer to each hole. Water thoroughly after planting and mulch around the base with 2 to 3 inches of straw or wood chips, keeping mulch 2 inches away from the stem to prevent rot. Stake or cage indeterminate varieties at planting time rather than waiting—doing it later risks damaging roots.

Second plantings for fall harvest in warm climates

If you live where the first frost arrives in late October or November, you can plant a second tomato crop in mid-summer for a fall harvest. Count backward from your first autumn frost date: tomatoes need 60 to 85 days to produce fruit depending on variety. If your first frost is November 1, plant by mid-August at the latest.

Summer soil is often too hot for seed germination (above 85°F kills pollen and prevents fruit set). Buy seedlings instead of starting seeds, and choose faster-maturing varieties labeled 60 to 70 days. Plant in afternoon shade if possible, water deeply and frequently, and expect slower growth in late summer heat. Fall-planted tomatoes often produce fewer but sweeter fruits as temperatures cool.

Common planting mistakes and how to avoid them

The most frequent error is planting too early when soil is still cold. Cold soil causes seeds and seedlings to sit dormant, rot, or grow extremely slowly. Even if air temperature reaches 70°F, soil may still be 50°F. Always check soil temperature before planting, not just calendar date or air temperature.

The second mistake is skipping hardening off. Seedlings moved directly from a warm, sheltered indoor space to outdoor sun and wind often develop sunscald (white or yellow patches on leaves) or wilt severely. Hardening off takes only ten days and prevents weeks of stunted growth or plant death. A third common error is planting too close together, which traps moisture and invites fungal disease. Stick to spacing guidelines even if it feels wasteful at planting time.

Frequently Asked Questions

Can I plant tomatoes before the last frost date if I use row covers?

Row covers protect seedlings from frost but do not warm the soil. If soil temperature is below 60°F, seedlings will still sit dormant or rot regardless of frost protection. Wait for soil to warm, then use row covers if a late frost is forecast after planting.

What if my seedlings are already flowering when it is time to plant?

Flowering seedlings often drop flowers after transplanting and take longer to recover. Pinch off flowers before planting if possible. The plant will redirect energy into root development instead of fruit, and you will get more total fruit later by starting with a stronger root system.

Is it too late to plant if it is already June?

It depends on your first frost date. If your first frost arrives in late October or November, you can still plant in early June and harvest before frost. If frost comes in September, June planting may not give you enough time. Count the days from planting to your first frost and choose a variety that matures in that window.

Do I need to wait for nighttime temperatures to stay above 50°F?

Yes. Tomatoes stop growing and become stressed below 50°F at night. While they will not die from a single cold night, consistent temperatures below 50°F slow growth dramatically. Wait until nighttime lows are reliably above 50°F before removing row covers or hardening off seedlings completely.

Can I plant tomatoes in containers on a different schedule than in-ground plants?

Container soil warms faster than garden soil in spring, so you can plant containers a week or two earlier. However, containers also dry out faster and heat up more in summer, so you will water more frequently. Follow the same soil temperature rule: wait until container soil reaches 60°F before planting.