Plant tomatoes outside after your last spring frost and when soil reaches 60°F
Tomatoes cannot survive frost. A single night below 32°F will kill seedlings or young plants, and even temperatures in the 40s will stunt their growth and make them vulnerable to disease. The safest time to move tomatoes into the garden is after your last frost date has passed and the soil has warmed to at least 60°F—ideally 65°F or higher.
Your last frost date is the average date of the final frost in spring for your specific location. This date varies dramatically by region: it might be mid-April in the South, late May in the Midwest, or early June in cold climates. Planting before this date is the single most common reason tomato plants fail or grow very slowly in the first weeks outdoors.
You can find your last frost date by searching online for "[your city] last frost date" or by contacting your local cooperative extension office. Once you know the date, mark it on a calendar and plan to transplant seedlings one to two weeks after it passes, once the soil has had time to warm.
Key Takeaways
- Tomatoes planted before the last frost date will be killed or severely damaged by cold nights, so waiting is more important than planting early.
- Your last frost date is specific to your location and can be found through a web search or your local cooperative extension office.
- Soil temperature matters as much as air temperature—wait until soil reaches 60°F before transplanting, even if daytime air is warm.
- Hardening off seedlings (gradually exposing them to outdoor conditions) for 7 to 10 days before planting reduces transplant shock and cold damage.
- In very short growing seasons, starting seeds indoors 6 to 8 weeks before the last frost date gives you mature plants ready to go the moment it is safe to plant.
How to Check Your Soil Temperature
A soil thermometer is inexpensive and takes the guesswork out of planting. Push the probe 4 inches into the soil in the spot where you plan to plant, wait 2 to 3 minutes, and read the temperature. Do this in the morning before the sun has warmed the surface, and check it on three separate days to make sure the warmth is consistent, not a one-day spike.
If you do not have a thermometer, you can use the hand test: wet your hand, push it 4 inches into the soil, and hold it there for one minute. If the soil feels cold or cool, it is below 60°F. If it feels neutral or slightly warm, it is probably ready. This method is less precise, but it works in a pinch.
Soil warms more slowly than air, especially in clay or wet soil. Even if daytime temperatures reach 70°F or 80°F, the soil may still be in the 50s. Planting into cold soil slows root growth, invites root rot, and can cause the plant to sit dormant for weeks instead of growing. Waiting for the soil to catch up is worth the delay.
Hardening Off Seedlings Before Transplanting
Seedlings started indoors are tender and will wilt or die if moved directly from a warm, sheltered windowsill to the outdoor garden. Hardening off means gradually exposing them to wind, direct sun, and temperature swings over 7 to 10 days so they toughen up and adjust to outdoor conditions.
Start by placing seedlings in a sheltered, shaded spot outdoors for 2 to 3 hours on the first day. Each day, increase the time outdoors and move them into more direct light. By day 7 or 8, they should be outside all day. If nighttime temperatures will stay above 50°F, leave them out overnight as well. Bring them inside if frost is forecast.
Hardened-off plants are stockier, darker green, and much less likely to go into shock when transplanted. Skipping this step is a common reason seedlings look pale and stunted for weeks after planting, or fail to grow at all.
Spacing and Planting Depth for Transplants
Dig a hole slightly deeper than the root ball of your seedling. Tomatoes have the ability to grow roots all along their buried stem, so you can plant them deeper than they were growing in their pot—bury the stem up to the first true leaves if the seedling is tall and leggy. This creates a stronger root system and helps the plant anchor itself in the soil.
Space plants 24 to 36 inches apart, depending on the variety. Determinate (bush) types can be closer; indeterminate (vining) types need more room for air circulation. Crowded plants are more prone to fungal disease because leaves stay wet longer after rain or watering. Water gently after planting and keep the soil consistently moist (not soggy) for the first two weeks while roots establish.
What to Do If Frost Is Forecast After Planting
If an unexpected frost is predicted within a few days of planting, cover plants with row covers, old sheets, or even upside-down buckets on the night of the frost. Remove the covers in the morning once temperatures rise above freezing. This straightforward step can save a crop that would otherwise be lost.
If plants are already in the ground and frost damage occurs, do not pull them out when ready. Wait a few days to see if they recover. Many tomato plants can bounce back from light frost damage, especially if the damage is only to the leaves and not the main stem. Remove any blackened or mushy leaves and let the plant regrow.
Regional Planting Windows
Planting dates vary widely depending on where you live. The table below shows approximate last frost dates for different regions, but your specific location may differ by a week or two. Use this as a starting point and confirm your exact date through a local search or extension office.
| Region | Approximate Last Frost Date | Typical Transplant Window |
|---|---|---|
| Deep South (zones 8–9) | Mid-April | Late April to early May |
| Mid-Atlantic and Upper South (zones 6–7) | Late April to early May | Mid-May to early June |
| Midwest (zones 5–6) | Mid-May | Late May to early June |
| Northeast (zones 4–5) | Late May to early June | Early to mid-June |
| Pacific Northwest (zones 8–9) | Mid-May | Late May to early June |
Starting Seeds Indoors to Extend Your Growing Season
If your growing season is short, start seeds indoors 6 to 8 weeks before your last frost date. This gives you mature, hardened-off seedlings ready to plant the moment conditions are right, rather than waiting to buy transplants or starting seeds outdoors. Tomato seeds germinate best at 70°F to 80°F and need bright light (a grow light or sunny windowsill) once they sprout to prevent them from becoming leggy.
Seedlings started indoors will be ready to transplant outside at the right time if you time the seed-starting date correctly. A seedling that is 6 to 8 inches tall with several sets of true leaves is ideal for transplanting. Anything taller or more mature may struggle after transplanting; anything smaller may not have enough root development to establish quickly.
Frequently Asked Questions
Can I plant tomatoes if the daytime temperature is warm but nights are still cold?
No. Nighttime temperature is what matters most. If nights are still dropping into the 40s or below, wait. Tomatoes will not grow in cold soil and are at high risk of disease. Warm days and cold nights create stress that stunts the plant for weeks. Wait until nighttime lows stay consistently above 50°F and soil is 60°F or warmer.
What happens if I plant tomatoes too early?
Early-planted tomatoes often sit dormant in cold soil for weeks, during which time they are vulnerable to root rot and fungal disease. Even if they survive, they grow very slowly and may never catch up to plants planted at the right time. The plant may also flower and set fruit late, reducing your total harvest before fall frost arrives.
Do I need to harden off seedlings if I buy transplants from a nursery?
Nursery-grown transplants are usually already hardened off or close to it, especially if they have been outside in a garden center. However, if they have been indoors under lights, give them 3 to 5 days of gradual outdoor exposure before planting. This is less critical than hardening off home-grown seedlings, but it still reduces transplant shock.
Is it ever too late to plant tomatoes?
Yes. Tomatoes need 60 to 85 days from transplanting to first ripe fruit, depending on the variety. If you plant after mid-summer in most climates, the plants may not mature before fall frost arrives. Check the days-to-maturity on the seed packet or transplant label and count backward from your average first fall frost date to know your latest safe planting date.
Can I plant tomatoes in containers if the ground is still too cold?
Containers warm up faster than ground soil, so this can work as a temporary solution. Use a dark-colored pot at least 5 gallons in size, fill it with potting soil (not garden soil), and place it in full sun. The soil will warm faster than the ground. Once ground soil reaches 60°F, you can transplant the container tomato into the garden if you wish, or leave it in the pot for the season.