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

The single most important date for tomato planting is your last spring frost date. Tomatoes are killed by frost—even a light freeze will blacken the leaves and stop growth. Find your frost date by searching "[your city] last frost date" or checking the USDA Hardiness Zone Map. Once you know that date, wait until it has passed, then check your soil temperature with a soil thermometer. Tomatoes germinate poorly and grow slowly in cold soil; they need at least 60°F to start, and 70°F or warmer for strong growth.

If you are starting from seed indoors, begin 6 to 8 weeks before your last frost date. If you are buying transplants from a nursery, you can plant them directly into the ground as soon as the frost date passes and soil is warm enough. Do not rush—a tomato planted into 50°F soil will sit dormant for weeks while one planted into 70°F soil will take off when ready.

Key Takeaways

  • Your last spring frost date is the hard important date; tomatoes planted before it will be killed by cold.
  • Soil temperature matters as much as air temperature—wait until soil reaches at least 60°F, ideally 70°F or warmer.
  • If starting from seed indoors, count backward 6 to 8 weeks from your frost date to know when to sow.
  • Transplants from a nursery can go in the ground when ready after the frost date if soil is warm enough.
  • Planting too early into cold soil wastes weeks of growing time; waiting a few weeks for warmth pays off in faster growth.

How to find your last frost date

Your last frost date is the average date of the final frost in spring for your location. It varies by region—Florida's might be in February, while Minnesota's might be in May. The easiest way to find it is to search "[your city or zip code] last frost date" online. The National Weather Service and most state agricultural extension offices publish these dates.

You can also check the USDA Hardiness Zone Map at planthardiness.ars.usda.gov. Enter your zip code and it will show your zone. Once you have your zone, search for the frost date associated with it. Keep in mind that these are averages, not guarantees—frost can occur a week or two after the average date in some years. If you want to be extra cautious, plant a week or two after the official date.

Checking soil temperature before planting

Air temperature and soil temperature are not the same. A warm day does not mean the soil is warm. Buy a soil thermometer (they cost $5 to $15 at garden centers) and push it 4 inches into the ground where you plan to plant. Take the reading in the morning, before the sun has warmed the surface. Do this for a few days in a row to get an average.

Tomatoes will grow in 60°F soil, but they grow slowly and are more prone to disease. At 70°F or warmer, they take off. If your frost date has passed but soil is still cold, wait another week or two and check again. You can speed up soil warming by laying black plastic or landscape fabric over the bed for a week before planting—it traps heat and raises soil temperature by several degrees.

Starting seeds indoors versus buying transplants

If you start tomato seeds indoors, sow them 6 to 8 weeks before your last frost date. They need warmth (70°F to 80°F) and bright light to germinate and grow stocky. Place them under grow lights or on a sunny windowsill, and keep the soil moist but not waterlogged. When seedlings have their first true leaves (the second set to appear), thin them or move them to individual pots so they have room to grow.

Buying transplants from a nursery or garden center is simpler if you do not have grow lights or indoor space. Look for plants that are 6 to 8 inches tall, have thick stems, and are not already flowering. Avoid tall, spindly plants or those already in bloom—they are stressed and will take longer to recover after planting. You can plant nursery transplants directly into the ground as soon as the frost date passes and soil is warm.

Hardening off seedlings before moving them outside

If you started seeds indoors, your seedlings have been in a sheltered environment with steady warmth and no wind. Before planting them outside, they need to adjust to outdoor conditions over 7 to 10 days. This process is called hardening off. Start by placing seedlings in a shaded, sheltered spot outdoors for 1 to 2 hours. Each day, increase the time outside and gradually move them into more sun and wind. By the end of the week, they should be able to spend a full day and night outside.

Hardening off prevents sunburn (pale patches on leaves) and wilting. Skip this step and your seedlings will look stressed for weeks after planting. If you buy transplants from a nursery, they have usually been hardened off already, so you can plant them directly.

Planting depth and spacing

Tomatoes can be planted deeper than they were growing in their pot. Bury the stem up to the first true leaves—roots will form all along the buried stem, creating a stronger root system. Space plants 24 to 36 inches apart, depending on the variety. Determinate (bush) types can be closer; indeterminate (vining) types need more room.

Water well after planting and keep the soil consistently moist for the first week or two while roots establish. Mulch around the base with 2 to 3 inches of straw or wood chips to retain moisture and keep soil temperature steady.

Adjusting timing for containers and season extension

If you are growing tomatoes in containers, you can plant a week or two earlier than in-ground growers because container soil warms faster than garden soil. Use a large pot—at least 5 gallons for determinate varieties, 10 gallons or larger for indeterminate types. Fill it with potting mix (not garden soil) and water it well before planting.

If you want to extend the season and grow tomatoes later into fall, plant a second crop 8 to 10 weeks before your first fall frost date. This works best in warm climates. In cooler regions, a late planting may not have time to produce fruit before frost arrives.

Frequently Asked Questions

Can I plant tomatoes before the last frost date if I cover them?

Row covers and frost cloth can protect seedlings from light frost (down to about 28°F), but they are not reliable for a hard freeze. If frost is forecast after you plant, covering helps, but it is safer to wait until the frost date has passed. The few weeks you gain are not worth the risk of losing your plants.

What if my soil is still cold on the frost date?

Wait. A warm air temperature does not mean warm soil. Check soil temperature with a thermometer. If it is below 60°F, wait another week or two and check again. Planting into cold soil delays growth more than waiting a few weeks does.

Is it too late to plant if I missed the frost date window?

No, but the later you plant, the less time tomatoes have to mature before fall frost. If you are more than a month past your frost date, look for early-maturing varieties (60 to 70 days to harvest) rather than long-season types. Container growing also speeds up harvest because the soil warms faster.

Do I need to harden off nursery-bought transplants?

Most nursery transplants have been hardened off already, so you can plant them directly. If you are unsure, spend a few days acclimating them anyway—it does not hurt and ensures they transition smoothly.

What happens if I plant tomatoes too early?

Frost will kill them, or cold soil will stunt their growth for weeks. Even if they survive, they sit dormant while you wait for warmth. A tomato planted three weeks late into warm soil will often catch up to and outpace one planted early into cold soil.