Start tomatoes indoors 6 to 8 weeks before your last spring frost, or direct-seed outdoors after the soil warms to 60°F

The timing depends on whether you're starting from seed indoors or buying transplants to put straight in the ground. If you start seeds indoors under lights, count backward from your area's last frost date — that's the date when freezing temperatures typically stop. Sow seeds 6 to 8 weeks before that date. If you're buying seedlings from a nursery and planting them outside, wait until after your last frost date and the soil has warmed to at least 60°F, ideally closer to 65°F or 70°F.

Tomatoes are frost-sensitive. A single hard freeze will kill the plant, even if it's already flowering or producing fruit. Planting too early is one of the most common mistakes home gardeners make — the seedling sits in cold soil, stops growing, and often rots before it ever takes off.

Key Takeaways

  • Find your last spring frost date by searching "[your city] last frost date" — this is the anchor date for all tomato timing decisions.
  • Start seeds indoors 6 to 8 weeks before that date if you want to grow from seed; transplants go in the ground after the date passes and soil reaches 60°F or warmer.
  • Soil temperature matters more than air temperature — a soil thermometer costs $10 and prevents the most common planting mistake.
  • Hardening off (gradually exposing indoor seedlings to outdoor conditions) takes 7 to 10 days and must happen before transplanting, or the plants will wilt and stop growing.

Finding your last frost date

Your last frost date is the average date of the final freeze in spring for your specific location. Search "[your city] last frost date" or "[your zip code] last frost date" to find it. The USDA also publishes an interactive map at planthardiness.ars.usda.gov where you can enter your zip code and see your zone and frost dates.

This date is an average, not a may provide. Some years the last frost comes earlier, some years later. But it's the standard gardeners use to time planting across the country. If your last frost date is May 15, you count backward 6 to 8 weeks to figure out when to start seeds indoors — roughly mid-March to early April.

Starting seeds indoors under lights

Fill a seed tray or small pots with seed-starting mix (not garden soil — it's too dense and holds too much water). Moisten the mix before planting. Plant seeds about 1/4 inch deep, one or two per cell. Cover the tray loosely with a humidity dome or plastic wrap to keep moisture in while seeds germinate.

Tomato seeds germinate in 5 to 10 days at room temperature (68°F to 75°F is ideal). Once sprouts appear, remove the cover and place the tray under grow lights or on a sunny windowsill. Keep lights 2 to 3 inches above the seedlings and run them 14 to 16 hours a day. Without enough light, seedlings become tall and spindly and won't transplant well.

Water from below by setting the tray in a shallow pan of water for 10 to 15 minutes, then removing it. This keeps the soil moist without waterlogging it. Once seedlings have their first true leaves (the second set to appear), thin to one plant per cell by snipping off the weaker one with scissors.

Hardening off before transplanting outdoors

About 7 to 10 days before your last frost date, start hardening off your seedlings. This means gradually exposing them to outdoor conditions so they adjust to wind, direct sun, and temperature swings. Indoor seedlings are tender and will wilt or stop growing if moved outside suddenly.

Day 1: Place seedlings in a sheltered spot outdoors (against a wall, under an eave) for 1 to 2 hours in indirect light. Bring them back inside. Day 2: Leave them out for 3 to 4 hours, still in shade. Day 3 and onward: Gradually increase time outside and introduce dappled sunlight, then partial direct sun. By day 7 to 10, they should handle a full day outside and some direct morning sun. Bring them in at night if temperatures drop below 50°F.

Transplanting seedlings into the garden

Wait until after your last frost date and the soil has warmed to 60°F or higher. Check soil temperature with a soil thermometer pushed 4 inches into the ground in the morning. If you don't have a thermometer, wait at least 1 to 2 weeks after your last frost date — by then the soil usually has warmed enough.

Dig a hole slightly deeper than the seedling's root ball. Tomatoes can be planted deeper than they were growing in the pot — bury the stem up to the first true leaves, and roots will form along the buried stem, creating a stronger plant. Space plants 24 to 36 inches apart depending on the variety (check the seed packet or plant label). Water thoroughly after planting.

Direct-seeding tomatoes outdoors

You can skip the indoor step and plant seeds directly in the garden, but it's slower. Wait until soil reaches 65°F to 70°F and all frost danger has passed — usually 2 to 3 weeks after your last frost date. Plant seeds 1/4 inch deep, 2 to 3 seeds per spot, spaced 24 to 36 inches apart. Thin to one plant per spot once seedlings have their first true leaves.

Direct-seeded tomatoes will flower and produce fruit 2 to 3 weeks later than transplants, so you'll harvest later in the season. In short-season areas (northern regions with frost arriving in early September), starting indoors gives you a better chance of getting a full harvest before cold weather returns.

Timing for different tomato types

Determinate tomatoes (bush types that ripen most fruit at once) and indeterminate tomatoes (vining types that produce all season) both follow the same planting timeline. The difference is in how long they grow and when they stop producing. Start both types at the same time — 6 to 8 weeks before your last frost date if starting from seed.

Cherry tomatoes and heirloom varieties germinate and grow at the same rate as standard slicing tomatoes, so timing is the same. The seed packet will tell you days to maturity (usually 60 to 85 days from transplant to first ripe fruit), but that's measured from transplant time, not from seed-starting time.

Common mistakes to avoid

Planting too early. Cold soil stops root growth and invites rot. If you plant a seedling in 50°F soil, it will sit there for weeks doing nothing while roots rot. Wait for warmth.

Skipping hardening off. Moving a seedling from a warm, still, indoor environment directly into wind and sun causes wilting and stunted growth. The plant may survive but will be set back by weeks.

Starting seeds too early. If you start seeds 10 or 12 weeks before your frost date instead of 6 to 8, seedlings will be overgrown and root-bound by transplant time. They'll be harder to harden off and slower to recover in the garden.

Planting too deep in pots. Seedlings need light to grow stocky. If they're buried under soil in their starting containers, they'll stretch toward the light and become weak and spindly.

Frequently Asked Questions

What if I don't know my last frost date?

Search your city name and "last frost date" online, or visit the USDA Plant Hardiness Zone Map at planthardiness.ars.usda.gov and enter your zip code. You'll see your zone and frost dates. If you're still unsure, ask a local garden center or cooperative extension office — they know the typical dates for your area.

Can I plant tomatoes earlier if I use row covers or cloches?

Yes, row covers and plastic cloches trap heat and can protect seedlings from frost. However, you still need soil temperature of at least 60°F for roots to grow. Covers help with air temperature but don't warm the soil much. Remove covers once temperatures stay above 50°F at night to prevent overheating.

What if my seedlings are already too tall and spindly?

Plant them deeper than usual — bury the stem up to the first true leaves. Roots will form along the buried stem, and the plant will be more stable. Move the seedlings closer to the light source and run lights 14 to 16 hours daily going forward. Spindly seedlings will still produce, but they're weaker and more prone to breaking.

How long after planting will I get tomatoes?

Transplants usually flower 4 to 6 weeks after planting and produce ripe fruit 8 to 12 weeks after planting, depending on variety. Direct-seeded plants take 2 to 3 weeks longer overall. Check the seed packet or plant label for the specific variety's days to maturity.

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. Follow the same timing — wait until after your last frost date and soil (potting mix) is warm. Container soil warms faster than garden soil, so you may be able to plant a week or two earlier, but still wait until nighttime temperatures stay above 50°F.