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

The single most important date for tomato planting is your last spring frost date. Tomatoes are killed by frost, so planting before that date wastes seeds and seedlings. You can find your frost date by searching "[your city] last frost date" or checking the USDA Plant Hardiness Zone Map with your zip code.

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, ideally 65°F to 70°F. You can measure soil temperature with a soil thermometer pushed 4 inches into the ground, checked in early morning. If you plant into soil colder than 60°F, the plant will stall for weeks before growing.

In most of the United States, this means planting between mid-April and late May. Southern regions (zones 9 and 10) can plant as early as February or March. Northern regions (zones 3 and 4) may not plant until late May or early June. The timing shifts by several weeks depending on where you live.

Key Takeaways

  • Never plant tomatoes before your last spring frost date, which you can find by searching your city name and "last frost date."
  • Soil temperature must reach 60°F or higher, measured 4 inches deep in the morning, or seedlings will sit dormant and may rot.
  • Transplants (seedlings started indoors) go in the ground 6 to 8 weeks after your last frost date, when they have at least two sets of true leaves.
  • Direct seeding (planting seeds outdoors) happens 1 to 2 weeks after transplant time, when soil is warmer and seeds germinate faster.
  • In warm climates (zones 9–10), you can plant a second crop in late summer for a fall harvest before the first frost.

Transplants vs. direct seeding: which method and when

Most home gardeners start with transplants — seedlings grown indoors under lights, then moved outside. This method gives you a head start and lets you choose exactly which varieties to grow. Start seeds indoors 6 to 8 weeks before your last frost date. Transplants are ready to move outside when they have at least two sets of true leaves (the leaves that look like tomato leaves, not the first smooth seed leaves) and are 3 to 4 inches tall.

If you buy transplants from a nursery, plant them out 1 to 2 weeks after your last frost date, once nighttime temperatures stay above 50°F. Hardening off — moving them outdoors for a few hours each day for a week — toughens them before planting. Skip this step and a sudden move from a warm greenhouse to outdoor sun and wind will shock the plant and slow growth.

Direct seeding (planting seeds straight into garden soil) works if you live where the growing season is long enough. Plant seeds 1 to 2 weeks after your last frost date, when soil is warmer and seeds germinate faster. Seeds take 6 to 8 days to sprout in warm soil, versus 2 to 3 weeks in cool soil. Direct seeding saves money but gives you less control over plant spacing and variety selection.

Soil temperature and nighttime conditions matter more than the calendar

A calendar date is a guideline, not a rule. The real signal is soil temperature and nighttime lows. Tomatoes stop growing when nighttime temperatures drop below 55°F, and they suffer stress below 50°F. Even if your frost date has passed, if nighttime lows are still in the 40s, wait another week or two. A plant sitting in cold soil and cold nights will yellow, stall, and attract pests.

If you plant too early and a late frost is forecast, cover plants with a frost cloth, row cover, or even old sheets the night before. Remove the cover the next morning once temperatures rise above freezing. This buys you a week or two without replanting.

Soil warms faster in raised beds and containers than in ground beds, so you can plant 1 to 2 weeks earlier in raised beds if you use them. Dark soil also warms faster than light soil. If you want to plant as soon as possible, lay black plastic or landscape fabric over the bed for 2 to 3 weeks before planting to trap heat.

Spacing and depth for transplants in the ground

When you move a transplant into the garden, bury it deeper than it was growing in the pot. Tomatoes can form roots all along the buried stem, which creates a stronger root system. Bury the stem up to the lowest set of leaves — you can remove lower leaves first if they're crowded. This deeper root system helps the plant survive dry spells later in the season.

Space transplants 24 to 36 inches apart, depending on the variety. Determinate types (bush tomatoes that grow to a fixed size) need 24 inches. Indeterminate types (vining tomatoes that grow all season) need 36 inches. Closer spacing shades the soil and keeps it cooler, but it reduces air flow and increases disease risk in humid climates. If you live in a humid area, space them farther apart.

Water transplants deeply after planting, then keep soil consistently moist (not soggy) for the first 2 to 3 weeks while roots establish. After that, water deeply but less often — about 1 to 2 inches per week depending on rain and heat.

Hardening off seedlings before moving them outside

Seedlings grown indoors under lights are soft and tender. Moving them directly into outdoor sun, wind, and temperature swings stresses them and slows growth for weeks. Hardening off means gradually exposing them to outdoor conditions over 7 to 10 days.

Start by placing seedlings in a sheltered spot outdoors (against a wall, under an eave, or in a cold frame) for 1 to 2 hours on the first day. Each day, add 1 to 2 more hours and move them into more direct sun and wind. By day 7 or 8, they can stay outside all day. Leave them outside overnight once nighttime temperatures stay above 50°F. After 10 days of this gradual exposure, they're ready to plant in the garden.

If you skip hardening off or rush it, plants will wilt, leaves will turn purple or yellow, and growth will pause for 2 to 3 weeks while they recover. The few extra days of hardening off pay back tenfold in faster establishment and earlier fruit.

Fall planting in warm climates

If you live in zones 9, 10, or 11 (southern California, southern Texas, Florida, and similar warm regions), you can plant a second tomato crop in late summer for a fall and early winter harvest. Plant transplants 8 to 10 weeks before your first fall frost date. This gives plants time to flower and set fruit before cold weather stops growth.

Fall-planted tomatoes often produce better fruit than spring plantings in very hot climates, because they mature in cooler weather. In zones 9 and 10, you may be able to grow tomatoes nearly year-round by staggering plantings 8 weeks apart. Check your local frost dates to know when to stop planting in fall.

Common mistakes that delay or kill tomato plants

Planting too early is the most common mistake. Soil below 60°F causes seeds to rot and transplants to sit dormant for weeks. Even if the air feels warm, check soil temperature before planting. A soil thermometer costs $10 and saves weeks of wasted time.

Skipping hardening off or rushing it stresses plants and delays growth by 2 to 3 weeks. Spend the time. Planting in waterlogged or compacted soil also kills roots and invites disease. Amend heavy clay with compost before planting, and make sure water drains away within a few hours after watering.

Planting too deep (burying the whole stem instead of just the lower part) can rot the buried stem if soil stays cold and wet. Planting too close together reduces air flow and increases fungal disease. Both mistakes are straightforward to make but hard to fix once plants are in the ground.

Frequently Asked Questions

Can I plant tomatoes before the last frost date if I use a cold frame or row cover?

Yes, but only 1 to 2 weeks early. A cold frame or row cover protects against light frost but not hard freezes. If temperatures drop below 28°F, even covered plants will die. Use covers as a buffer, not a may provide. Remove covers during warm days so plants don't overheat.

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

Wait for soil to warm up. Air temperature and soil temperature are different. Soil warms slowly, especially in spring. A warm week of air temperature doesn't mean soil has warmed. Check with a soil thermometer before planting. Planting in cold soil wastes seeds and seedlings.

How do I know if my transplants are ready to move outside?

Transplants are ready when they have at least two sets of true leaves (leaves that look like tomato leaves, not the smooth seed leaves) and are 3 to 4 inches tall. They should be sturdy and not leggy or pale. If they're tall and thin, they need more light before moving outside.

Can I plant tomatoes in containers instead of the ground?

Yes. Containers warm faster than ground soil, so you can plant 1 to 2 weeks earlier. Use a container at least 5 gallons for determinate types and 10 gallons for indeterminate types. Fill with potting mix (not garden soil), and water more often because containers dry out faster than ground beds.

What should I do if a late frost is forecast after I've planted?

Cover plants with frost cloth, row cover, or old sheets the night before the frost. Anchor the cover so it doesn't blow away. Remove it the next morning once temperatures rise above freezing. This can protect plants through a light frost and save you from replanting.