Plant tomatoes outside after your last 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 date of the final frost in your area. Tomatoes cannot survive frost. They stop growing below 50°F at night and suffer damage or death at 32°F and below. Planting too early is the most common reason tomato seedlings fail.
You can find your last frost date by searching "last frost date [your city]" or by entering your zip code at almanac.com/gardening/frostdates. The date varies dramatically by location—it might be mid-April in Georgia, late May in Michigan, or early June in Montana. Do not guess or use a neighboring state's date.
Beyond frost safety, wait until soil temperature reaches at least 60°F. Cold soil slows root growth and invites root rot. You can measure soil temperature with a soil thermometer (available at any garden center for $10–15) or check your local cooperative extension website, which often posts weekly soil temperatures for your county.
Key Takeaways
- Your last frost date is the hard important date—tomatoes planted before it will likely die, even if seedlings look healthy.
- Soil temperature matters as much as air temperature; wait until soil reaches 60°F, which usually happens 1–2 weeks after the last frost date.
- Hardening off seedlings (gradually exposing them to outdoor conditions over 7–10 days) prevents transplant shock and sunburn.
- Planting too early in cold soil causes root rot and stunted growth that cannot be fixed later, so waiting an extra week is safer than rushing.
How to Find Your Exact Last Frost Date
Your last frost date is specific to your location, not your state or region. Two towns 20 miles apart can have frost dates two weeks different because of elevation, proximity to water, and local geography. Using the wrong date is a common mistake that costs gardeners their entire crop.
The fastest way to find it is to search "last frost date [your city, state]" in any search engine. The USDA Hardiness Zone Map and the Almanac's frost date tool both appear in the top results. If you live in a rural area or small town, search your county name instead—your county cooperative extension office maintains frost date data and often posts it on their website.
Write down the date and mark it on a calendar. This is the earliest safe day to plant tomatoes in the ground. If you plant seedlings before this date and frost arrives, the plants will die regardless of how healthy they looked in the nursery.
Checking Soil Temperature Before Planting
Even after your last frost date passes, the soil may still be too cold. Tomato roots grow slowly in soil below 60°F, and the plant becomes vulnerable to root rot and fungal diseases. Waiting for warm soil prevents these problems and actually gets your tomatoes growing faster in the long run.
Buy a soil thermometer at a garden center or online for $10–20. Push it 4 inches into the soil in the morning, wait 2 minutes, and read the temperature. Check the same spot for three days in a row. If it reads 60°F or higher on all three days, the soil is warm enough. If it dips below 50°F at night, wait another week and check again.
If you do not want to buy a thermometer, contact your local cooperative extension office. They test soil temperature weekly during spring and post the results online. Search "[your county] cooperative extension soil temperature" to find the data for your area.
Hardening Off Seedlings Before Transplanting
Seedlings started indoors are soft—they have never felt wind, direct sun, or temperature swings. Moving them straight from a warm windowsill to the garden will shock them and stunt their growth or kill them. Hardening off means gradually exposing seedlings to outdoor conditions over 7–10 days so they toughen up.
Start by placing seedlings outside in a sheltered spot (against a wall, under an eave) for 2–3 hours on the first day. Each day, leave them out longer and move them to a slightly more exposed location. By day 7–10, they should spend the full day and night outside. Then they are ready to plant in the ground.
If you skip hardening off and plant seedlings directly in the garden, they often wilt, turn purple or yellow, stop growing, or die within a week. The extra 10 days of gradual exposure saves weeks of recovery time later.
Regional Planting Windows
Planting dates vary widely across North America. The table below shows typical windows, but always use your own last frost date and soil temperature—these are averages and your location may differ.
| Region | Typical Last Frost Date | Typical Soil Warm Enough | Typical Outdoor Planting Window |
|---|---|---|---|
| Deep South (Georgia, Alabama, Louisiana) | Mid-April | Late April | Late April–May |
| Mid-Atlantic (Virginia, Maryland, Pennsylvania) | Mid-May | Late May | Late May–early June |
| Midwest (Ohio, Indiana, Illinois) | Late May | Early June | Early–mid-June |
| Northern states (Michigan, Wisconsin, Minnesota) | Late May–early June | Mid-June | Mid-late June |
| Mountain West (Colorado, Utah, Wyoming) | Late May–early June | Mid-late June | Late June–early July |
| Pacific Northwest (Oregon, Washington) | Late April–early May | Mid-May | Mid-late May |
What Happens If You Plant Too Early
Planting tomatoes in cold soil or before the last frost date causes several problems. Seedlings may survive a light frost but will be severely damaged—leaves turn black, stems split, and the plant rarely recovers. Even if frost does not arrive, cold soil slows root growth so much that the plant sits stunted for weeks while waiting for warmth.
Cold soil also invites root rot and damping-off disease, which kill seedlings from the soil up. Once root rot starts, no amount of watering or fertilizer fixes it. The plant dies, and the disease can linger in the soil. Waiting until soil is warm prevents these diseases entirely.
The temptation to plant early is strong—garden centers sell seedlings in March and April, and neighbors may plant before you. Resist it. Planting two weeks late in warm soil produces healthier, faster-growing plants than planting early in cold soil. You will harvest tomatoes at nearly the same time or earlier because the plants grow so much faster once they are warm.
Frequently Asked Questions
Can I plant tomatoes if the forecast shows frost after I plant them?
No. If frost is in the forecast within the next week, wait. Even a light frost kills tomato seedlings. Check the 10-day forecast before planting, and if frost appears anywhere in that window, delay planting until the frost risk is gone.
What if I planted too early and frost is coming?
Cover the plants with blankets, cardboard, or frost cloth the night before frost arrives. Remove the cover the next morning when temperatures rise above 50°F. This buys you a few days, but it is not a long-term solution—if multiple frosts are forecast, it is better to wait and replant after the danger passes.
Does it matter if I plant in the morning or evening?
Evening is slightly better because seedlings have all night to recover from transplant shock before facing full sun the next day. Morning planting works fine if you water well and shade the plants for a few days. Avoid planting in the hottest part of the afternoon.
Can I plant tomatoes in containers earlier than in the ground?
Slightly earlier, because you can move containers to shelter if frost threatens. But soil temperature still matters—container soil warms faster than ground soil, so you may be able to plant 1–2 weeks earlier. Still wait until soil temperature reaches 60°F and your last frost date has passed.
What if my area has two frost dates—spring and fall?
Use the spring last frost date to plant. The fall first frost date tells you when to stop planting new seedlings (usually 8–10 weeks before the first fall frost), but it does not affect when you plant in spring.