Plant tomatoes in New Jersey between mid-May and early June for the best results

New Jersey's last frost date falls between May 10 and May 20, depending on which part of the state you live in. Tomatoes cannot survive frost, so you should wait until after that date to move seedlings outdoors. Most gardeners in New Jersey plant between May 15 and June 1, when soil has warmed to at least 60°F and ideally closer to 65°F or higher.

Soil temperature matters more than air temperature for tomatoes. Even if the air feels warm, cold soil will stunt growth and invite disease. Use a soil thermometer to check before planting. If you plant too early into cold soil, the seedlings may sit dormant for weeks, and you lose the advantage of an early start.

Key Takeaways

  • New Jersey's last frost date is between May 10 and May 20, and you should not plant tomatoes outdoors until after that date passes.
  • Soil temperature should reach 60°F minimum, ideally 65°F or warmer, which usually happens in mid-to-late May across the state.
  • Northern New Jersey (zones 6a and 6b) plants later than southern areas (zones 7a and 7b), so check your specific zone before choosing a planting date.
  • Starting seeds indoors 6 to 8 weeks before your target outdoor planting date gives you strong seedlings ready to transplant in May.

How to find your exact last frost date in your county

New Jersey spans two hardiness zones. Northern counties including Bergen, Essex, and Morris are in zone 6a or 6b, with last frost dates around May 15 to May 20. Southern counties including Atlantic, Cape May, and Cumberland are in zone 7a or 7b, with last frost dates around May 1 to May 10. The state's central region falls in between.

The easiest way to find your exact date is to enter your zip code into the USDA Hardiness Zone Map on planthardiness.ars.usda.gov. The map shows your zone and links to frost date information for your area. Your county's Cooperative Extension office also publishes frost dates—search "[your county] New Jersey Cooperative Extension" to find their website with local planting calendars.

Once you know your last frost date, add two weeks as a safety margin. This accounts for unexpected cold snaps in late spring, which happen in New Jersey most years. Planting on May 25 instead of May 15 costs you almost nothing in harvest time but eliminates the risk of losing seedlings to a surprise freeze.

Starting seeds indoors so seedlings are ready in May

Tomato seeds need 6 to 8 weeks of indoor growing before they are large enough to transplant outside. If your last frost date is May 15, count back 6 to 8 weeks and start seeds indoors around March 15 to April 1. This timing gives you stocky, healthy seedlings with true leaves by mid-May, ready to go into the ground as soon as soil warms.

Sow seeds indoors in seed-starting mix under grow lights or on a sunny windowsill. Keep soil moist but not waterlogged, and maintain temperatures between 70°F and 75°F for germination. Once seedlings sprout, lower the temperature slightly to 65°F to 70°F and provide 14 to 16 hours of light daily. This prevents them from becoming leggy and weak.

Harden off seedlings about 10 days before transplanting by gradually exposing them to outdoor conditions. Start with 1 to 2 hours in a sheltered spot, then increase time and exposure over a week. This toughens the plants so they do not wilt when moved to full sun and outdoor air.

Soil preparation and temperature checks before planting

Prepare your garden bed 2 to 3 weeks before planting by mixing in compost or aged manure. Tomatoes are heavy feeders and need rich, well-draining soil. Work amendments into the top 8 to 10 inches of soil. If your soil is clay-heavy, add extra compost to improve drainage and prevent root rot.

Check soil temperature with a soil thermometer inserted 4 inches deep. Take readings in the morning for three consecutive days. If the average is 60°F or higher, you can plant. In New Jersey, this usually happens by May 15 to May 20 in the north and May 10 to May 15 in the south, but weather varies year to year. A cool, wet spring may delay warm soil until early June.

If you are eager to plant but soil is still cold, use black plastic mulch or landscape fabric to warm the soil faster. Lay it down 2 to 3 weeks before planting to trap heat. Cut holes through it when you transplant, and leave it in place through the season to retain warmth and moisture.

Choosing between early, mid-season, and late varieties

Early varieties like 'Early Girl' and 'Stupice' mature in 50 to 65 days and are ideal if you want tomatoes by mid-July. Plant these in mid-May. Mid-season varieties like 'Brandywine' and 'Cherokee Purple' need 70 to 85 days and should go in the ground by late May to ripen before frost. Late varieties like 'Mortgage Lifter' need 85 to 100 days and must be planted by early June at the latest.

New Jersey's first fall frost typically arrives between October 10 and October 20. Count backward from that date to see how many growing days you have. If your first frost is October 15 and you plant on June 1, you have about 136 days—enough for any variety. If you plant on June 15, you have only 122 days, which rules out the slowest varieties.

Growing multiple varieties with different maturity dates spreads your harvest across the season. Plant early types in mid-May, mid-season types in late May, and late types in early June. This way, you get fresh tomatoes from July through the first frost.

Common mistakes that delay or damage early tomatoes

Planting too early is the most common mistake. Seedlings set in cold soil do not grow faster—they sit still, stressed, and vulnerable to disease. You lose weeks instead of gaining them. Wait for soil to warm, even if it means planting a week later than you hoped.

Overwatering newly transplanted seedlings is the second mistake. Wet soil invites fungal diseases and root rot. Water deeply but infrequently, allowing the top inch of soil to dry between waterings. Drip irrigation or soaker hoses deliver water to roots without wetting foliage, which also prevents disease.

Planting seedlings too deep or too shallow affects root development. Bury the stem up to the first true leaves—tomatoes will root along the buried stem and develop a stronger root system. Do not plant so deep that the soil covers the lowest leaves, which can rot. Space plants 24 to 36 inches apart to allow air circulation.

Protecting young plants from late spring cold and wind

Even after your last frost date, unexpected cold snaps can damage tender seedlings. Keep row covers or frost cloth on hand. If temperatures drop below 50°F after planting, drape the covers over plants in the evening and remove them during the day. This straightforward step can save a crop.

New Jersey springs are often windy, which can break young stems or dry out soil rapidly. Install stakes or cages at planting time so you do not disturb roots later. Tie seedlings loosely to supports with soft twine. A windbreak of taller plants or a fence on the north side of the bed reduces stress on young plants.

Mulch around plants with 2 to 3 inches of straw or shredded leaves once soil has warmed. Mulch keeps soil temperature stable, retains moisture, and prevents soil-borne diseases from splashing onto lower leaves. Keep mulch a few inches away from the stem to prevent rot.

Frequently Asked Questions

Can I plant tomatoes in New Jersey in April?

No. Soil is still too cold in April across New Jersey, and frost risk is very high. Seedlings planted in April will sit dormant in cold soil and often rot before they grow. Wait until mid-May in the north or early May in the south.

What if my seedlings are ready but the soil is still cold?

Harden them off and keep them in a sheltered spot outdoors for a few more weeks, or pot them up into larger containers and grow them on indoors under lights. Do not plant them in cold soil. Waiting a week or two for soil to warm is faster than dealing with diseased or stunted plants.

Is it too late to plant tomatoes in June in New Jersey?

Early and mid-season varieties can still produce if planted by early June, though you will harvest later in the fall. Late varieties planted after June 10 may not ripen before the first frost. Check the maturity days on the seed packet and count backward from your expected first frost date.

Do I need to use a soil thermometer?

A soil thermometer costs about $10 and removes guesswork. If you do not have one, wait until soil feels warm to the touch several inches down and the air has been above 60°F for at least a week. This is less precise but works in a pinch.

What happens if I plant tomatoes and frost comes after?

Cover plants with frost cloth, blankets, or row covers before sunset and remove them after sunrise. Water the soil deeply before covering—moist soil holds heat better than dry soil. If frost kills the above-ground growth, the plant may regrow from the roots, though it will be set back several weeks.