Plant tomatoes outside after your last spring frost and when soil reaches 60°F
The safest time to move tomato seedlings into the garden is when nighttime temperatures stay above 50°F and your soil has warmed to at least 60°F. Most gardeners plant between two and four weeks after their region's last spring frost date. Tomatoes are frost-sensitive plants—a single cold night below 50°F will stall their growth, and frost will kill them outright. Planting too early wastes the seedling's energy on survival rather than growth.
Your last spring frost date is the average date when frost stops occurring in your area. You can find this date through your local cooperative extension office, which publishes frost calendars for each county. Search "[your county] cooperative extension frost date" or visit your state's extension website directly. This date is not a may provide—frost can arrive after it—but it marks the statistical boundary most gardeners use to decide when the risk is low enough.
Key Takeaways
- Find your last spring frost date through your county's cooperative extension office, which publishes frost calendars specific to your area.
- Wait until nighttime temperatures consistently stay above 50°F and soil temperature reaches 60°F, which usually happens one to four weeks after the frost date.
- Plant in the morning or on an overcast day to reduce transplant shock, and harden off seedlings by exposing them to outdoor conditions for seven to ten days first.
- A soil thermometer costs under $10 and removes guesswork—stick it 4 inches into the ground in the morning to check actual soil temperature.
- If you plant too early and frost threatens, cover plants with blankets or row covers the night before and remove them the next morning.
How to find your last frost date
Your county cooperative extension is the official source for frost dates in your area. Search online for "[your state] cooperative extension" plus your county name, or go directly to your state's land-grant university extension website. Once you find the office, look for a frost date calendar or frost date tool. Some states publish interactive maps where you enter your zip code and get the exact date.
If you cannot locate the date online, call your local extension office directly—they answer this question constantly and can tell you over the phone. The frost date is usually listed as a single date in spring (when frost stops) and another in fall (when it returns). Write both down; the spring date tells you when to plant tomatoes, and the fall date helps you know when to harvest before cold arrives.
Online tools like the Almanac's frost date finder or Gardening Know How's frost calculator also work if you enter your zip code, though the cooperative extension remains the most reliable source for your specific location.
Checking soil temperature before planting
Soil temperature matters more than air temperature. Tomato roots will not absorb water or nutrients efficiently in cold soil, even if the air feels warm during the day. Buy a soil thermometer—they cost $8 to $15 and last for years. Push the probe 4 inches into the ground in the morning, wait 30 seconds, and read the temperature. Do this in the spot where you plan to plant, not in a shaded area or near a building.
Soil warms slowly in spring, especially in clay or wet soil. If your frost date has passed but soil is still below 60°F, wait another week or two. Planting into cold soil causes seedlings to sit dormant, which stresses them and invites root rot. Once soil reaches 60°F and stays there, your tomatoes will grow steadily. Ideally, soil should be 65°F to 70°F for fastest growth, but 60°F is the minimum threshold.
Hardening off seedlings before moving them outside
Seedlings grown indoors under lights are tender and will wilt or burn if moved directly into full sun and wind. Harden them off by gradually exposing them to outdoor conditions over seven to ten days. Start by placing seedlings in a sheltered, shaded spot outdoors for two to three hours on day one. Each day, increase the time outside and gradually move them into brighter light.
By day seven or eight, seedlings should spend the full day outside in dappled shade or morning sun. On the final days before planting, leave them out overnight if temperatures stay above 50°F. This process toughens the plant tissue and prepares the seedling for the stress of transplanting. Skipping this step often results in stunted growth or leaf damage that takes weeks to recover from.
Planting technique and timing of day
Plant in the early morning or on an overcast day to reduce transplant shock. Dig a hole slightly larger than the seedling's root ball and set the plant at the same depth it was growing in its pot—or slightly deeper if the seedling is tall and leggy, since tomatoes can root along buried stems. Water thoroughly after planting and keep the soil consistently moist for the first two weeks while roots establish.
Space plants 24 to 36 inches apart depending on the variety. Determinate (bush) types can be closer; indeterminate (vining) types need more room. Avoid planting on hot, sunny afternoons when the seedling is already stressed from the move. Morning planting gives roots time to settle before the heat of the day.
What to do if frost threatens after planting
If frost is forecast within a week of planting, your young seedlings are at risk. Cover plants with blankets, row covers, or even large pots the evening before frost arrives. find the cover so wind does not blow it away, and remove it the next morning once temperatures rise above freezing. This straightforward step can save a crop that would otherwise be lost.
If you have already planted and a hard frost (below 28°F) arrives unexpectedly, the plants will likely die. To avoid this, many gardeners wait until two weeks after the frost date before planting, which gives a safety margin. Others plant earlier but keep row covers or frost blankets on hand and ready to deploy.
Regional timing examples
Timing varies widely by location. In the upper Midwest and Northeast, last frost dates typically fall between May 10 and May 31, so outdoor planting happens in late May or early June. In the Mid-Atlantic, frost dates are usually April 20 to May 10, allowing planting in mid-to-late May. In the South and Southwest, frost dates arrive in March or early April, so planting can begin in April or even late March.
Gardeners in frost-free zones (southern Florida, southern California, southern Texas) can plant tomatoes in fall or winter instead, since their concern is heat and drought rather than frost. Check your specific frost date rather than assuming your region follows a national pattern.
Frequently Asked Questions
Can I plant tomatoes before the last frost date if I use row covers?
Yes, row covers provide some frost protection and can extend your planting window by one to three weeks. However, they also trap heat and moisture, so monitor plants closely and remove covers on warm days to prevent overheating. This method works best for gardeners willing to manage covers actively rather than set them and forget them.
What if my seedlings are already tall and leggy indoors?
Bury the stem deeper than it was growing in the pot—tomatoes root along buried stems and will develop a stronger root system. Plant it at an angle if needed. This does not solve the problem of weak growth indoors, but it helps the plant recover once it is outside in full light.
How long after planting will tomatoes start producing fruit?
Most varieties begin flowering four to six weeks after planting and produce ripe fruit eight to ten weeks after that, so expect your first harvest in mid-to-late summer. Early varieties are faster; late-season varieties take longer. This timeline assumes consistent warmth, water, and sunlight.
Is it better to plant from seed directly in the garden or start seedlings indoors?
Starting indoors six to eight weeks before your frost date gives you larger plants that fruit earlier. Direct seeding in the garden works but delays harvest by several weeks since seeds take time to germinate and grow. Most home gardeners start indoors for faster results.
What happens if I plant tomatoes in soil that is still too cold?
Cold soil slows root growth and water uptake, causing seedlings to sit dormant or decline. Roots may rot if soil stays wet and cold. The plant will eventually grow once soil warms, but you lose weeks of growing time and stress the seedling unnecessarily.