Plant tomatoes outside after your last frost date, when soil reaches 60°F and daytime temperatures stay above 50°F

The single most important date for outdoor tomato planting is your last spring frost date. Tomatoes die when exposed to frost. If you plant before that date arrives, a late freeze will kill your seedlings. Your local cooperative extension office or a frost date calculator (search "last frost date" plus your zip code) will give you the exact date for your area.

Beyond the frost date, soil temperature matters as much as air temperature. Tomato roots grow slowly in cold soil and may rot before they establish. Wait until soil reaches at least 60°F, ideally 65°F or warmer. You can check soil temperature with an inexpensive soil thermometer from any garden center. If you plant into soil colder than 60°F, the plant will sit dormant and stressed for weeks, even if air temperatures are warm.

Daytime air temperature should stay consistently above 50°F before you plant. Nighttime temperatures below 50°F slow growth and can cause flower drop on young plants. If a warm spell arrives before your frost date, resist planting — a single cold night will set the plant back further than waiting another week.

Key Takeaways

  • Your last spring frost date is the hard important date; planting before it almost always results in dead seedlings.
  • Soil temperature of 60°F or higher matters more than air temperature alone, because cold soil stops root growth and invites rot.
  • Nighttime temperatures below 50°F will stall growth and drop flowers even if daytime warmth seems ready.
  • Hardening off seedlings for 7 to 10 days before planting reduces transplant shock and helps them survive temperature swings.

How to Find Your Last Frost Date

Your last frost date is the average date of the final frost in spring for your specific location. It varies by region, elevation, and proximity to water. A frost date 50 miles away may not match yours. The most reliable source is your state's cooperative extension office, which maintains frost date maps based on decades of local weather records.

To find it, search "[your state] cooperative extension last frost date" or visit your county extension office directly. Many extension websites have interactive maps where you enter your zip code and get the date when ready. The USDA also maintains a searchable frost date database. Once you have the date, mark it on a calendar — this is your planting window's starting point.

Hardening Off Seedlings Before Planting

Seedlings grown indoors are tender. Moving them directly from a warm, still, protected environment to outdoor sun and wind will shock them. Hardening off — gradually exposing seedlings to outdoor conditions over 7 to 10 days — toughens the plant tissue and reduces transplant failure.

Start by placing seedlings in a sheltered spot outdoors (against a wall, in dappled shade) for 2 to 3 hours on the first day. Each day, increase the time outside and expose them to more direct sun and wind. By day 7 or 10, they should spend the full day and night outside. This process thickens the stem, darkens the leaves, and prepares the plant for the stress of transplanting and outdoor conditions.

If you skip hardening off and plant directly, expect wilting, leaf burn, and slow recovery. The plant may survive, but it will lag behind a hardened-off plant by 2 to 3 weeks.

Soil Preparation Before Planting

Tomatoes are heavy feeders and need rich, well-draining soil. Before planting, work compost or aged manure into the top 8 to 10 inches of soil. This improves drainage, adds nutrients, and creates a loose structure for roots to penetrate. If your soil is clay-heavy or compacted, amending it now prevents waterlogging and root rot later.

Test your soil pH if possible. Tomatoes prefer slightly acidic soil between 6.0 and 6.8. If your soil is very acidic (below 6.0) or alkaline (above 7.0), you can adjust it with lime or sulfur, but this takes weeks to work. If you are planting soon, focus on adding organic matter instead, which buffers pH over time.

Spacing and Planting Depth

Space tomato plants 24 to 36 inches apart, depending on the variety. Determinate (bush) types can be closer; indeterminate (vining) types need more room for air circulation. Crowded plants develop fungal diseases because leaves stay wet longer.

Plant seedlings deeper than they grew in their pot. Bury the stem up to the first true leaves — tomatoes will root along the buried stem, creating a stronger root system. This is one of the few times deeper planting actually helps. Water well after planting and keep soil consistently moist (not waterlogged) for the first 2 to 3 weeks while roots establish.

Regional Timing Examples

Timing varies widely by region. In the upper Midwest and Northeast, last frost dates fall between May 15 and June 1, so outdoor planting happens in late May or early June. In the mid-Atlantic and upper South, frost dates are typically April 15 to May 15, allowing planting in mid-to-late May. In the lower South and Gulf Coast, frost dates arrive in March or early April, so planting can begin in late April or May.

In warm climates with no spring frost (southern Florida, southern California, Hawaii), the limiting factor shifts to heat and day length rather than frost. In these areas, tomatoes planted in fall or winter often perform better than spring plantings, because they mature as temperatures cool slightly. Check with your local extension office for region-specific guidance.

What to Do If an Unexpected Frost Arrives

If you planted and a frost warning appears in the forecast, cover plants with blankets, row covers, or even cardboard boxes on the night of the frost. Remove covers the next morning so plants do not overheat. This emergency protection can save young plants if the frost is light (32°F to 35°F). A hard freeze (below 28°F) will kill most tender plants regardless of covering.

If plants are killed by frost, you have two options: replant new seedlings once the danger passes, or wait and see if the plant regrows from the base. Some tomato plants will sprout new growth from the roots if the top is killed, but this delays fruiting by several weeks. Replanting is usually faster.

Frequently Asked Questions

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

Row covers reduce frost risk but do not eliminate it. A hard freeze will kill plants even under covers. Planting 1 to 2 weeks before your frost date with covers is possible if you monitor the forecast closely and are prepared to add extra layers or remove covers during warm days. Most gardeners find it simpler to wait until after the frost date.

What if my soil is still cold but the air temperature is warm?

Wait for soil to warm. Cold soil slows root growth and invites rot, and no amount of warm air will fix that. If you are impatient, you can warm soil by laying black plastic over the bed for 1 to 2 weeks before planting. This traps heat and raises soil temperature 5 to 10 degrees.

Is it better to plant in spring or fall in warm climates?

In areas with mild winters (USDA zones 9 and warmer), fall planting often works better than spring planting. Tomatoes planted in late summer or early fall mature as temperatures cool, avoiding the intense heat that reduces fruit set and flavor. Spring plantings in these areas may struggle through peak summer heat. Check with your local extension for the best planting window for your specific location.

How long does it take from planting to first fruit?

Most tomato varieties produce fruit 60 to 85 days after transplanting, though this varies by variety and growing conditions. Early varieties mature faster; large slicing types take longer. Consistent warmth, adequate water, and full sun speed up fruiting. Cool weather or stress delays it.

Can I plant tomatoes in containers instead of the ground?

Yes. Container tomatoes follow the same frost date and temperature rules as in-ground plants. Use a pot at least 5 gallons for determinate varieties and 10 gallons for indeterminate types. Containers warm faster than soil in spring, so you may be able to plant a week or two earlier, but monitor nighttime temperatures and be ready to move pots indoors if frost threatens.