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 is warm. Tomatoes are frost-sensitive plants that will rot in cold soil and die if exposed to freezing temperatures. In most of the United States, this means planting between mid-April and late May, but the exact date depends entirely on where you live.

You can find your local frost date by searching "last frost date" plus your zip code, or by contacting your county extension office. That date tells you the average day of the last spring frost in your area. Plant tomatoes one to two weeks after that date, not on it. By then, soil has warmed enough for seeds to germinate and roots to develop without rotting.

Soil temperature matters more than air temperature. A thermometer stuck 4 inches into the ground should read at least 60°F, ideally 65°F or warmer. Even if daytime air temperatures are in the 70s, cold soil will stall growth and invite disease. If you plant too early, seedlings will sit dormant in the ground for weeks, wasting time and risking rot.

Key Takeaways

  • Plant tomatoes one to two weeks after your area's last spring frost date, which you can find by searching your zip code online.
  • Soil temperature must reach 60°F (ideally 65°F or higher) before planting, measured 4 inches below the surface with a soil thermometer.
  • Starting seeds indoors six to eight weeks before your frost date gives you transplants ready to go into warm soil at the right time.
  • Hardening off seedlings by exposing them to outdoor conditions for one to two weeks before planting prevents transplant shock and strengthens stems.

Starting seeds indoors versus buying transplants

You have two routes: start seeds indoors under lights, or buy seedlings from a nursery and transplant them. Starting from seed costs less and gives you more variety, but requires grow lights, heat mats, and space. Buying transplants is faster and simpler if you have a local nursery with healthy plants in stock.

If you start seeds indoors, sow them six to eight weeks before your last frost date. This timing means seedlings will be 6 to 8 inches tall and ready to harden off (gradually expose to outdoor conditions) by the time soil warms up. Seeds germinate best in a seed-starting mix kept at 70–75°F with consistent moisture and 14 to 16 hours of light daily from a grow light positioned 2 to 3 inches above the seedlings.

Nursery transplants should be stocky, dark green, and free of yellow leaves or visible roots poking through drainage holes. Avoid leggy, pale seedlings that have been crowded or under-watered. A healthy transplant is 6 to 8 inches tall with at least two sets of true leaves (the leaves that look like tomato leaves, not the first rounded seed leaves).

Hardening off seedlings before planting

Seedlings started indoors or bought from a nursery have never felt wind, direct sun, or temperature swings. Planting them straight into the garden causes transplant shock—wilting, stunted growth, or death. Hardening off takes one to two weeks and is non-negotiable if you want strong plants.

Start by setting seedlings outdoors in a sheltered, shaded spot for one to two hours on a mild day. Each day, gradually increase time outdoors and move them into more direct light. By day 7 to 10, they should spend the full day outside. By day 10 to 14, they can stay out overnight if temperatures stay above 50°F. If a cold night is forecast, bring them back inside.

Watch for wilting or leaf damage during hardening off. If plants look stressed, move them back to shade or indoors for a day, then resume more slowly. This process toughens the stems and prepares roots to handle outdoor conditions without shock.

Planting depth and spacing in the garden

Tomatoes are unusual: they can be planted deeper than they grew in their pot, and they will develop roots all along the buried stem. This creates a stronger root system. Remove the lower leaves and bury the stem up to the lowest remaining leaves, or even up to the first true leaf cluster if the seedling is very tall and leggy.

Space plants 24 to 36 inches apart, depending on variety. Determinate (bush) types need less space; indeterminate (vining) types need more. Crowded plants have poor air circulation, which invites fungal diseases like early blight and powdery mildew. If you are planting in rows, space rows 36 to 48 inches apart so you can walk between them and reach fruit.

Dig a hole slightly larger than the root ball, set the plant in at the deeper depth, and backfill with soil mixed with compost. Water when ready and thoroughly to settle soil around the roots. 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 and pest damage.

Regional planting timelines

Planting dates vary widely across North America. In the Deep South (zones 8–9), tomatoes can go in the ground in late March or early April. In the Upper Midwest and Northeast (zones 4–5), wait until mid-May or even late May. In the Pacific Northwest, late April to early May is typical. In the Southwest, you may plant in early spring and again in late summer for a fall crop.

Your USDA hardiness zone and local frost date are the most reliable guides. A frost date search takes 30 seconds and beats guessing. If you live in an area with unpredictable spring weather, wait an extra week after the frost date to be safe—the delay costs you less than losing seedlings to a late freeze.

Common mistakes that delay or damage plants

Planting too early is the most common error. Cold soil causes seeds to rot before they sprout, and seedlings to sit stunted for weeks. Even if they survive, they grow slowly and are more vulnerable to disease. Waiting one extra week for soil to warm is always worth it.

Skipping hardening off or rushing it causes transplant shock. Seedlings wilt, leaves turn purple or brown, and growth stalls for weeks. A two-week hardening-off period takes patience but saves you from replanting or losing plants entirely.

Planting too close together creates humid conditions that invite fungal disease. Crowded plants also compete for water and nutrients, producing smaller fruit and fewer of them. Stick to the spacing guidelines even if it feels sparse at first—plants grow quickly and will fill the space.

Burying the stem too shallowly misses the benefit of a deeper root system. Bury as deep as you can without covering the lowest leaves. This anchors the plant better and helps it weather drought and wind.

Frequently Asked Questions

Can I plant tomatoes in containers instead of the ground?

Yes. Use a pot at least 5 gallons for determinate varieties and 10 gallons for indeterminate types. Fill with potting soil (not garden soil), and follow the same planting depth and timing rules. Containers warm up faster than ground soil, so you may be able to plant a week or two earlier. Water more often because containers dry out faster than garden beds.

What if my area gets a late frost after I plant?

If frost is forecast within a week of planting, cover plants with row covers, blankets, or cloches at night. Remove covers during the day so plants get light and air. If plants are already in the ground and frost hits, water them thoroughly before the freeze—moist soil holds heat better than dry soil. Most seedlings survive a light frost (32°F) if the soil is warm and moist.

Can I plant tomatoes in fall instead of spring?

In warm climates (zones 9–10), yes. Plant in late summer so plants mature and fruit before the first fall frost. In cooler areas, fall planting does not work because plants will not have time to produce fruit before cold weather arrives. Check your first fall frost date and count backward 60 to 80 days (the time from planting to first ripe fruit) to see if fall planting is possible in your area.

How do I know if my soil is warm enough without a thermometer?

A soil thermometer costs $5 to $15 and is the most reliable method. If you do not have one, wait until daytime air temperatures consistently stay above 70°F and nighttime lows stay above 55°F for at least a week. This usually means soil has warmed enough, but it is not may provide. Buying a thermometer removes the guesswork.

Should I use fertilizer when planting?

Mix compost into the planting hole, but hold off on high-nitrogen fertilizer. Nitrogen promotes leafy growth at the expense of flowers and fruit. Once plants start flowering (usually three to four weeks after planting), switch to a balanced or slightly higher-phosphorus fertilizer to encourage fruiting. Follow the package directions and do not over-fertilize, which causes excessive foliage and fewer tomatoes.