Plant tomatoes outside after your last spring frost and when soil reaches 60°F

The single most important date for outdoor tomatoes is your last spring frost date. Tomato plants die when exposed to frost, so planting before that date means starting over. You can find your frost date by searching "[your city or zip code] last frost date" — the National Weather Service publishes these for every region in the United States, and they vary by weeks depending on where you live.

Even after frost danger passes, 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, ideally 65°F or warmer. You can check soil temperature with a straightforward soil thermometer from any garden center — push it 4 inches into the ground in the morning. If you do not have a thermometer, a practical rule is to wait until nighttime temperatures stay above 50°F for a week.

The combination of these two conditions — no frost risk and warm soil — is what determines your planting window. In warm climates like southern Florida or southern Texas, this might be January or February. In cooler regions like Minnesota or Maine, it might not arrive until late May or early June.

Key Takeaways

  • Your last spring frost date is the hard important date — tomatoes planted before it will be killed by frost, so check your local date before you plant.
  • Soil temperature must reach 60°F or higher; cold soil causes seeds to rot and transplants to sit dormant and stressed.
  • Nighttime air temperature staying above 50°F for a week is a practical signal that soil has warmed enough, if you do not have a soil thermometer.
  • Hardening off transplants — gradually exposing them to outdoor conditions over 7 to 10 days — prevents shock and wilting when you move them outside.

How to find your last frost date

The easiest method is to search your location online. The National Weather Service maintains frost date data for thousands of locations across the country. Type "[your city] last frost date" or "[your zip code] last frost date" into a search engine and you will get a specific date or date range.

If you live in a rural area or a small town, search for the nearest larger city or your county seat instead. Frost dates shift by elevation and proximity to water, so if you live in the mountains or near a large lake, your actual date may be a week or two later than the nearest town. Local garden centers and county extension offices also have this information and can account for your specific location.

Why soil temperature is just as important as air temperature

Tomato seeds need soil at least 60°F to germinate reliably. Below that, they either do not sprout or sit in the ground long enough to rot from fungal diseases. Transplants planted into cold soil experience transplant shock — they stop growing, leaves yellow, and they become vulnerable to root diseases. Even if they survive, they grow slowly and produce less fruit later in the season.

A soil thermometer costs $10 to $20 and takes the guesswork out of planting. Push it 4 inches into the soil in the morning, wait 2 minutes, and read the temperature. Check it in the spot where you plan to plant, because soil in a sunny bed warms faster than soil in shade. If you are planting multiple beds, check each one.

Hardening off transplants before moving them outside

If you started tomato seedlings indoors under lights, they are adapted to stable indoor conditions — no wind, consistent temperature, and filtered light. Moving them directly outside is shock. Hardening off means gradually exposing them to outdoor conditions over 7 to 10 days so they toughen up.

Start by placing transplants in a sheltered spot outdoors for 2 to 3 hours on the first day — a porch, against a wall, or under a tree. Bring them back inside. Each day, add 2 to 3 hours of outdoor time and gradually move them to a sunnier, windier spot. By day 7 or 8, they can stay outside overnight if temperatures stay above 50°F. By day 10, they are ready to plant in the garden.

Skipping this step often results in wilted, bleached, or stunted plants that take weeks to recover. The few extra days of hardening off pay back in stronger growth and earlier fruit.

Planting depth and spacing for transplants

Bury tomato transplants deeper than they grew in their pots — up to the first true leaves. Tomato stems develop roots all along their buried length, creating a stronger root system. This is one of the few plants where deep planting is an advantage, not a mistake.

Space transplants 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 diseases because leaves stay wet longer after rain or watering.

What to do if frost threatens after you plant

If an unexpected frost is forecast after you have planted, cover plants with blankets, cardboard, or frost cloth before sunset. Anchor the cover to the ground so cold air does not slip underneath. Remove the cover the next morning once temperatures rise above freezing. This works for light frosts (28°F to 32°F) but not for hard freezes.

If a hard freeze is forecast and you have already planted, there is no reliable way to save the plants. Some gardeners in frost-prone areas wait an extra week or two past the official frost date to reduce this risk, even though it means a slightly shorter growing season.

Regional planting windows across the United States

Planting dates vary widely by region. The Pacific Northwest typically plants in late May or early June. The upper Midwest and Northeast plant in late May through early June. The mid-Atlantic and upper South plant in mid-May. The lower South and Gulf Coast plant in March or April. Southern Florida and southern Texas can plant in late winter or early spring.

These are general ranges — your specific date depends on your exact location, elevation, and proximity to water. A county extension office in your state can give you a more precise date for your area and can also advise on varieties that perform well in your climate.

Frequently Asked Questions

Can I plant tomatoes before the last frost date if I use row covers?

Row covers slow heat loss and can protect against light frosts, but they do not reliably protect against a hard freeze. Waiting until after the frost date is safer. If you do plant early with covers, monitor the forecast closely and be ready to add extra layers if temperatures drop below 28°F.

What if my soil is still cold but the frost date has passed?

Wait for soil to warm. A few extra weeks of delay costs you less than planting into cold soil, which causes root rot and stunts growth for the whole season. You can warm soil faster by laying black plastic mulch over the bed for a week or two before planting.

Do I need to harden off transplants if I buy them from a garden center?

Garden center transplants are usually already hardened off because they have been outdoors. You can plant them directly if they have been outside for at least a few days. If they came from a greenhouse and went straight into a car, give them 3 to 5 days of gradual outdoor exposure before planting.

Can I plant tomatoes in containers instead of the ground?

Yes. Containers warm faster than ground soil, so you can plant a week or two earlier. Use a large pot — at least 5 gallons for determinate types, 10 gallons for indeterminate — and fill it with potting mix, not garden soil. Container soil dries faster, so you will water more often.

What happens if I plant too early and frost kills my plants?

You can replant if you have time before the end of the growing season. Count backward from your first fall frost date to see how many days you have left. Most tomato varieties need 60 to 85 days to produce fruit, so if you have fewer than 70 days left, replanting may not give you a harvest before frost.