Plant tomatoes outdoors after your last spring frost date, when soil temperature reaches 60°F and ideally stays above 50°F at night
The single most important date for outdoor tomatoes is your last spring frost date—the average day when frost stops happening in your area. Tomatoes die when exposed to frost. You can find your frost date by entering your zip code into the USDA Hardiness Zone Map or by calling your local cooperative extension office.
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 before planting; 65°F to 70°F is better. You can check soil temperature with a soil thermometer, which costs $10 to $20 at any garden center. If you plant into soil colder than 50°F, the plant will struggle for weeks.
Night temperature is the real constraint. Even if daytime highs reach 70°F, if nights drop below 50°F consistently, tomatoes will not grow. They sit and sulk. Wait until nighttime lows stay reliably above 50°F for at least a week before planting.
Key Takeaways
- Find your last spring frost date using the USDA Hardiness Zone Map or your local cooperative extension—this is the hard important date for planting.
- Soil temperature must reach 60°F minimum, ideally 65°F to 70°F, which usually happens one to three weeks after the last frost date depending on your region.
- Night temperatures must stay above 50°F consistently; a single cold night after planting can stall growth for weeks.
- In cold climates, start seeds indoors six to eight weeks before your frost date so transplants are ready to go into the ground on time.
- In warm climates with no spring frost, plant when soil reaches 60°F, usually in late winter or early spring.
How to find your last frost date
The USDA Hardiness Zone Map is the standard tool. Go to planthardiness.ars.usda.gov, enter your zip code, and the map shows your zone. Each zone has an average last spring frost date. If you live in zone 5b, for example, your last frost date is around May 15. If you live in zone 9a, it might be April 1.
Your local cooperative extension office has the same information and can answer follow-up questions about your specific neighborhood, which matters because frost pockets—low-lying areas where cold air settles—can be 5 to 10 days colder than the surrounding area. If you live in a valley or near a large body of water, call the extension office to ask whether the standard date applies to your location.
Do not guess or use a date from the internet without confirming it matches your zip code. A frost two weeks after planting will kill young tomato plants.
Checking soil temperature before planting
A soil thermometer is the only reliable way to know if the ground is warm enough. Push it 4 inches into the soil in the morning, wait two minutes, and read the temperature. Do this for three to five days in a row. If the average is 60°F or higher, you can plant.
Soil warms slowly in spring. Even if air temperature hits 75°F during the day, soil may still be 50°F. Dark mulch, black plastic, or landscape fabric laid over the bed a week or two before planting will warm the soil faster. Remove plastic or fabric once you plant, or the soil will overheat in summer.
If you plant too early and soil is cold, seeds will rot and transplants will sit motionless for weeks. It is better to wait one more week than to plant into cold ground.
Starting seeds indoors versus buying transplants
If you start seeds indoors, sow them six to eight weeks before your last frost date. Seeds germinate best at 70°F to 80°F. Once they sprout, they need 14 to 16 hours of light per day from a grow light or sunny window. Without enough light, seedlings become leggy and weak.
Transplants should be 6 to 8 inches tall and have their first true leaves (the second set of leaves that appear) when you move them outdoors. Harden them off by setting them outside in a sheltered spot for a few hours each day, gradually increasing time outdoors over seven to ten days. This toughens the plant so it does not wilt when exposed to wind and direct sun.
If you buy transplants from a garden center, choose stocky plants with dark green leaves. Avoid tall, thin plants or those already flowering. A plant in flower will drop those flowers after transplanting because it is stressed by the move.
Planting depth and spacing outdoors
Bury the transplant deeper than it was growing in the pot—up to the first true leaves. Tomatoes develop roots all along the buried stem, which strengthens the plant. Space plants 24 to 36 inches apart depending on variety. Determinate (bush) types need less space; indeterminate (vining) types need more.
Water well after planting and keep soil consistently moist but not waterlogged for the first two weeks. A drip line or soaker hose works better than overhead watering because it keeps leaves dry and reduces disease.
Regional timing differences
In the northern United States (zones 3 to 5), last frost dates fall between May 1 and June 1. Soil does not warm to 60°F until late May or early June. Plant transplants rather than seeds directly in the ground, because the growing season is short and you need plants that are already established.
In the mid-Atlantic and Midwest (zones 5 to 7), last frost dates range from April 15 to May 15. You can direct-seed or transplant, but transplants give you a head start. Many gardeners plant twice—once in late spring and again in early summer for a fall harvest.
In the South and Southwest (zones 8 to 10), spring frost is rare or nonexistent. The constraint is heat, not cold. Plant in late winter or early spring so tomatoes mature before extreme summer heat arrives. In some areas, you can plant a second crop in late summer for a fall harvest.
What happens if you plant too early or too late
Plant too early and frost will kill the plant, or cold soil will cause roots to rot and leaves to yellow. The plant may survive but will be stunted for weeks. Plant too late and the tomato will not have enough warm growing days to produce fruit before fall frost arrives. In short seasons, a late start means no harvest.
If an unexpected frost is forecast after you have planted, cover plants with a sheet, blanket, or frost cloth the night before. Remove the cover the next morning when temperature rises. This buys you a few degrees of protection.
Frequently Asked Questions
Can I plant tomatoes before the last frost date if I use a frost cloth or row cover?
Frost cloth provides a few degrees of protection but is not reliable for hard freezes. It works best for light frosts (28°F to 32°F). If your area gets hard freezes below 25°F, wait until after the last frost date. If you do plant early with protection, monitor the forecast closely and be ready to cover plants every night.
What if my soil is still cold but the air is warm?
Wait for soil to warm. Air temperature and soil temperature are different. Soil warms slowly because it holds cold longer. Planting into cold soil causes root rot and stunted growth. Use a soil thermometer to check, and wait until it reads 60°F or higher.
Can I plant tomatoes in containers earlier than in the ground?
Yes, slightly. Container soil warms faster than ground soil because it is exposed to sun on all sides. You can plant containers one to two weeks before the last frost date if you are willing to move them indoors or cover them if frost threatens. Once nighttime lows stay above 50°F, leave containers outside permanently.
Do I need to wait for the last frost date if I live in a warm climate with no frost?
No. In frost-free zones, plant when soil reaches 60°F, which is usually late winter or early spring. The real constraint in warm climates is heat—tomatoes stop setting fruit when temperatures stay above 90°F at night. Plant early so the plant matures before peak summer heat.
What if I plant and then a cold snap happens?
Cover plants with a sheet or frost cloth the night before the freeze. Leave the cover on until midday when temperature rises. If the plant is already wilted or blackened by frost, it is dead and should be removed. Plant a replacement once the danger passes.