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

The best time to plant tomatoes is after the danger of frost has passed and the soil has warmed up. Tomatoes are warm-season plants that will not grow in cold soil and will die if exposed to frost. In most of the United States, this means planting between late April and early June, though the exact date depends on where you live.

Soil temperature matters more than air temperature. Even if the air feels warm during the day, cold soil will stunt tomato roots and invite root rot. Use a soil thermometer to check the temperature at 4 inches deep. Once it reads 60°F consistently, you can plant. Ideally, wait until soil reaches 65°F or higher for faster growth.

You can find your local frost date by searching "last frost date" plus your zip code, or by contacting your county extension office. They maintain records specific to your area and can tell you the average date when frost stops occurring in spring.

Key Takeaways

  • Plant tomatoes only after your last spring frost date has passed and soil temperature reaches at least 60°F, measured 4 inches deep.
  • Tomato seedlings started indoors 6 to 8 weeks before your frost date will be ready to transplant right when conditions are safe.
  • Planting too early in cold soil causes stunted growth, root rot, and weak plants that produce less fruit.
  • Your county extension office can tell you your exact frost date, which varies by region and sometimes by elevation within the same county.

How to find your local frost date

Your last spring frost date is the average date when frost stops occurring in your area. Search online for "last frost date" and your zip code, and you will find a map or database that shows the date for your location. The Almanac and the National Weather Service both maintain searchable frost date tools.

If you live in a region with variable elevation or microclimates, call your county extension office directly. They can tell you whether your specific neighborhood has an earlier or later frost date than the county average. This matters if you live on a hill, near a large body of water, or in a valley where cold air settles.

Starting seeds indoors versus buying transplants

You have two routes: start seeds indoors under grow lights, or buy seedlings from a nursery and transplant them outside. Starting seeds indoors takes 6 to 8 weeks before your frost date. Sow seeds in seed-starting mix under lights, keep the soil moist and warm (70°F to 75°F), and thin seedlings once they have two true leaves. This method costs less and gives you more variety choices.

Buying transplants from a nursery is faster and requires no equipment. Choose stocky, dark-green seedlings with no flowers yet. Leggy, pale seedlings or those already flowering will struggle after transplanting. Nursery seedlings are usually ready to plant out 2 to 3 weeks before your frost date, so you can harden them off (expose them gradually to outdoor conditions) before planting.

Hardening off takes 7 to 10 days. Place seedlings outside in a sheltered spot for 1 to 2 hours the first day, then gradually increase outdoor time and sun exposure each day until they stay out overnight. This prevents transplant shock and sunburn.

Soil preparation before planting

Tomatoes need rich, well-draining soil with plenty of organic matter. Work 2 to 3 inches of compost or aged manure into the top 8 to 10 inches of soil before planting. This improves drainage, adds nutrients, and creates a loose texture that roots can penetrate easily.

Test your soil pH if possible. Tomatoes prefer soil between 6.0 and 6.8 on the pH scale. If your soil is too acidic (below 6.0), add lime. If it is too alkaline (above 7.0), add sulfur. Your county extension office can run a soil test for a small fee and tell you exactly what amendments to add.

If you are planting in containers, use a quality potting mix rather than garden soil. Garden soil compacts in pots and drains poorly. A potting mix stays loose and drains well, which tomato roots need.

Common mistakes that delay or damage tomato growth

Planting too early is the most common mistake. Cold soil slows germination, causes root rot, and creates weak plants that take weeks to recover. Even if seedlings survive, they will sit dormant rather than grow. Wait for warm soil, even if it means planting later than you hoped.

Planting too deep is the second mistake. Bury the stem up to the lowest leaves if you want, because tomatoes will root along the buried stem. But do not bury the entire plant or cover the leaves with soil. Buried leaves rot and invite disease.

Overcrowding is another issue. Space determinate (bush) varieties 24 to 36 inches apart and indeterminate (vining) varieties 36 to 48 inches apart. Crowded plants have poor air circulation, which leads to fungal disease. Wider spacing also makes pruning and harvesting easier.

Adjusting planting time for your tomato variety

Different tomato varieties mature at different speeds. Early varieties like 'Early Girl' and 'Stupice' mature in 50 to 65 days and can be planted closer to your frost date. Mid-season varieties like 'Brandywine' and 'Cherokee Purple' take 70 to 85 days. Late-season varieties take 85 days or longer and need to be planted earlier so they finish before fall frost.

Count backward from your first fall frost date to know when to plant late varieties. If your first fall frost typically arrives October 15 and a variety takes 85 days to mature, plant by July 22. This gives the plant time to produce ripe fruit before cold weather stops growth.

If you live in a short-season area (fewer than 120 frost-free days), choose early and mid-season varieties. Long-season varieties will not have time to mature before frost arrives.

Extending the season with row covers and mulch

If you want to plant a few days before your frost date, use a floating row cover (lightweight fabric that lets light and water through) to protect seedlings from frost. Drape the fabric directly over plants and anchor the edges with soil or stones. Remove it once nighttime temperatures stay above 50°F.

Once plants are established, explore 2 to 3 inches of mulch around the base to keep soil warm and retain moisture. Straw, shredded leaves, or wood chips all work. Keep mulch 2 inches away from the stem to prevent rot.

Frequently Asked Questions

Can I plant tomatoes if there is still a chance of frost?

No. A single frost will kill tomato plants or set them back weeks. Wait until your frost date has passed. If frost is forecast after you have planted, cover plants with row covers or blankets overnight and remove them the next morning.

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

Wait for the soil to warm up. Air temperature can be 75°F while soil is still 55°F. Cold soil causes root rot and stunts growth far more than waiting a week or two. Use a soil thermometer to check before planting.

Can I plant tomatoes in summer if I missed the spring window?

Yes, but only if you have at least 60 to 70 frost-free days left before fall frost. Plant early or mid-season varieties in mid-summer and they may mature before cold weather arrives. Late-season varieties will not have time to finish.

Do I need to harden off seedlings I started indoors?

Yes. Seedlings grown indoors under lights are tender and will sunburn or wilt if moved directly outside. Harden them off over 7 to 10 days by gradually increasing outdoor time and sun exposure. This toughens the plant tissue and prevents transplant shock.

What happens if I plant tomatoes in soil that is too cold?

Cold soil slows root growth, invites root rot, and causes seedlings to sit dormant for weeks. Even if they survive, they will be weak and produce less fruit. The delay from planting too early usually costs you more time than waiting for warm soil.