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

The single most important rule for tomato planting is this: soil temperature matters more than calendar date. Tomato seeds and seedlings will rot in cold soil, no matter how eager you are to plant. Wait until the soil has warmed to at least 60°F, ideally 65°F or warmer. This typically falls two to three weeks after your region's last frost date, but the only way to know for certain is to check your soil temperature with a straightforward thermometer pushed 4 inches into the ground.

Your last frost date varies by location. If you do not know yours, search "last frost date" plus your zip code, or contact your local cooperative extension office — they maintain frost date records for your exact area. In the warmest parts of the United States (southern Florida, southern Texas, southern California), you may plant tomatoes twice a year, in spring and again in late summer for a fall harvest. In colder regions (northern New England, the upper Midwest), the window is narrow and late planting is not practical.

Key Takeaways

  • Soil temperature of 60°F or higher is the real trigger for planting, not the calendar date or last frost date alone.
  • You can start seeds indoors six to eight weeks before your last frost date, then move seedlings outside once soil warms.
  • Transplants (seedlings bought from a nursery) go in the ground at the same time as seeds — when soil reaches 60°F.
  • Hardening off (gradually exposing indoor seedlings to outdoor conditions) takes seven to ten days and must happen before transplanting.
  • In warm climates, a second planting in late summer can produce a fall crop before the first hard freeze.

Starting seeds indoors versus buying transplants

You have two paths: start seeds indoors under lights six to eight weeks before your last frost date, or buy seedlings from a nursery and plant them directly outdoors. Both work, and the choice depends on your setup and budget.

Starting seeds indoors gives you more variety — you can grow heirloom or specialty types that nurseries do not stock — and costs less per plant. You will need a sunny windowsill or grow lights, seed-starting soil, and containers with drainage holes. Keep soil moist but not waterlogged, and maintain temperatures around 70°F. Once seedlings develop their first true leaves (the second set to appear), thin them so each has room to grow without touching its neighbors.

Buying transplants from a nursery is faster and requires no equipment. Look for stocky plants with dark green leaves and no flowers yet — flowering seedlings are often stressed and will produce less fruit. Avoid leggy, pale plants that have been crowded on the shelf. Transplants cost more per plant but save you six to eight weeks of indoor care.

Hardening off seedlings before moving them outside

If you started seeds indoors, your seedlings have lived in a stable, protected environment. Moving them directly into the garden will shock them — they may wilt, stop growing, or die. Hardening off is the process of gradually exposing them to outdoor conditions over seven to ten days.

Begin by placing seedlings in a sheltered spot outdoors (a porch, against a south-facing wall) for one to two hours on the first day. Each day, increase the time outdoors and expose them to more direct sun and wind. By day seven or ten, they should spend the full day outside. On the final night, leave them out if temperatures stay above 50°F; otherwise, bring them in. Once they have hardened off, they are ready to transplant into the garden.

Nursery-bought transplants have usually been hardened off already, but check the tag or ask the staff. If they have been growing indoors under lights, give them a few days of gradual outdoor exposure before planting.

Spacing, depth, and soil preparation

Space tomato plants 24 to 36 inches apart, depending on the variety. Determinate types (bush tomatoes that grow to a fixed size) can be closer; indeterminate types (vining tomatoes that grow all season) need more room for air circulation and to prevent disease.

Plant seedlings deeper than they were growing in their pot — bury the stem up to the first true leaves. Tomatoes will develop roots along the buried stem, creating a stronger root system. Dig a hole, fill it with water, let it drain, then set the seedling in place and backfill with soil.

Prepare the planting area by mixing compost or aged manure into the top 8 to 10 inches of soil. Tomatoes are heavy feeders and benefit from organic matter that holds moisture and nutrients. If your soil is very poor, add a balanced fertilizer (such as 5-10-10) at planting time, following the package rate. Do not over-fertilize with nitrogen, which promotes leafy growth at the expense of fruit.

Protecting young plants from late frost

Even after you plant, a surprise frost can kill tender seedlings. If frost is forecast within a week of planting, cover plants with row covers, blankets, or cloches (bottomless plastic jugs work well) on the night of the frost. Remove covers the next morning once temperatures rise above 50°F.

If a hard freeze does kill your seedlings, you can replant. Soil will be warm by then, so new seedlings will grow quickly. Many gardeners in frost-prone areas deliberately wait an extra week or two after the official last frost date to reduce the risk of losing their investment.

Regional planting windows

Planting dates shift across the country. In the Southeast and mid-Atlantic (zones 6 to 8), plant after mid-April through early May. In the Midwest and Northeast (zones 4 to 5), wait until late May or early June. In the Southwest and California (zones 9 to 10), plant in early spring (February to March) and again in late summer (July to August) for a fall harvest. In the warmest zones (11 and above), tomatoes can grow year-round, though summer heat may slow fruiting.

These are rough guides. Your local cooperative extension office has frost date maps and planting calendars specific to your county. They also track which varieties perform best in your climate — some types tolerate heat better, others resist local diseases, and a few are bred for short seasons.

Frequently Asked Questions

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

You can plant a week or two early and cover plants on frost nights, but it adds work and risk. Soil below 60°F will still slow growth, so early planting does not save much time. Most gardeners find it simpler to wait until soil is warm.

What if I plant too early and the soil is cold?

Seeds will sit dormant or rot. Seedlings will yellow, stop growing, and may develop root rot. If you plant and then a cold snap hits, cover plants and wait for warmth. Do not replant until soil temperature rises again.

Can I plant tomatoes in containers instead of the ground?

Yes. Use a pot at least 5 gallons for determinate types, 10 gallons or larger for indeterminate types. Fill with potting soil (not garden soil), and follow the same planting depth and spacing rules. Containers warm faster than ground soil in spring, so you may be able to plant a week or two earlier.

How do I know when soil is warm enough if I do not have a thermometer?

A soil thermometer costs five to ten dollars and is worth it. Without one, wait until nighttime temperatures stay above 55°F for at least a week, and the ground feels warm to the touch when you dig. This is less reliable than a thermometer but works in a pinch.

Is it too late to plant tomatoes in June?

In most of the country, planting in June is late but not impossible. You will have a shorter harvest window before frost, but plants will still produce fruit. In very hot climates (Arizona, southern Texas), June planting is too late for spring crops; wait for late summer instead.