Plant tomatoes after the last frost date in your area, when soil temperature reaches 60°F or higher

The single most important rule for tomato planting is this: wait until the danger of frost has passed. A hard freeze will kill tomato seedlings and young plants outright. Your last frost date — the average date of the final frost in spring — is the earliest you should move tomatoes into the ground. In most of the United States, this falls between mid-April and late May, depending on where you live.

Soil temperature matters as much as air temperature. Tomatoes germinate poorly and grow slowly in cold soil. Wait until soil reaches at least 60°F before planting, and ideally 65°F or warmer. You can check soil temperature with a straightforward soil thermometer from any garden centre. Cold soil slows root development and invites fungal disease. Warm soil — 70°F and above — produces faster growth and stronger plants.

If you start seeds indoors under lights, begin them six to eight weeks before your last frost date. This gives seedlings time to grow sturdy before transplanting. If you buy seedlings from a nursery, you can plant them directly into the garden once conditions are right, without the indoor seed-starting step.

Key Takeaways

  • Plant tomatoes outdoors only after your area's last frost date has passed and soil temperature is at least 60°F.
  • If you start seeds indoors, sow them six to eight weeks before your last frost date so seedlings are ready to transplant.
  • Tomato seedlings need hardening off — gradual exposure to outdoor conditions — for seven to ten days before planting in the ground.
  • In hot climates, you may plant a second crop in late summer for a fall harvest, timing it so plants mature before the first frost.

How to find your last frost date

Your last frost date is specific to your location and changes year to year slightly, but averages are published for every region. The easiest way to find it is to search online for "last frost date" plus your city or zip code. The Almanac, local university extension offices, and garden websites all maintain searchable databases.

Once you know the date, mark it on your calendar. This is your signal to start seeds indoors if you are growing from seed, or to begin checking soil temperature if you are buying seedlings. Many gardeners also note their first frost date in fall — the average date of the first killing frost — because this determines when you must harvest all remaining tomatoes before they freeze.

Starting seeds indoors versus buying seedlings

Starting from seed indoors gives you more variety choices and costs less per plant, but requires grow lights, a warm spot, and attention to watering. Sow seeds indoors six to eight weeks before your last frost date in a seed-starting mix under fluorescent or LED lights. Keep soil warm — around 70°F — and moist but not waterlogged. Seedlings should emerge in five to ten days.

Buying seedlings from a nursery is faster and requires no equipment. You skip the indoor phase entirely and plant seedlings directly into the garden once conditions are right. Choose stocky, dark-green seedlings with no flowers yet. Leggy, pale seedlings or those already flowering often struggle after transplanting.

Either way, seedlings need hardening off before planting in the ground. This means gradually exposing them to outdoor sun, wind, and temperature swings over seven to ten days. Start by placing them outside in shade for an hour, then increase sun exposure and time outdoors each day. This toughens the plants and prevents transplant shock.

Soil preparation before planting

Tomatoes are heavy feeders and need rich, well-draining soil. Before planting, work compost or aged manure into the top six to eight inches of soil. This improves drainage, adds nutrients, and creates a loose texture that roots can penetrate easily. If your soil is clay-heavy or compacted, amending it now prevents waterlogging and root rot later.

Test your soil pH if possible. Tomatoes prefer slightly acidic soil between 6.0 and 6.8. If your soil is very alkaline or very acidic, you can adjust it, but this takes time. If you are planting in spring and soil pH is off, add sulfur to lower pH or lime to raise it, and wait a few weeks before planting so the amendment can work.

Spacing and depth when transplanting

Space tomato plants 24 to 36 inches apart, depending on the variety. Determinate types (bush tomatoes) can be closer; indeterminate types (vining tomatoes) need more room for air circulation. Poor spacing traps moisture and invites fungal disease.

Plant seedlings deeper than they grew in their pots. Bury the stem up to the first set of true leaves — tomatoes will root all along the buried stem, creating a stronger root system. This is one of the few cases where planting deeper is actually beneficial. Water well after planting and keep soil consistently moist for the first two weeks while roots establish.

Timing for warm climates and fall crops

In hot climates where summer temperatures exceed 90°F regularly, tomatoes may stop flowering and drop fruit. If this is your situation, you may have better success planting in late summer for a fall harvest. Count backward from your first frost date — tomatoes need 60 to 85 days from transplant to first ripe fruit, depending on variety. Plant seedlings in late July or August so they mature as temperatures cool in fall.

Some gardeners in mild climates grow tomatoes year-round, planting in spring for summer harvest and again in late summer for winter harvest. Check your local extension office for variety recommendations suited to fall and winter growing in your area.

Common planting mistakes to avoid

Planting too early is the most common mistake. Cold soil and frost kill seedlings or stunt them severely. Patience pays off — waiting two weeks longer usually results in faster growth overall because the plant is not struggling against cold.

Overcrowding is the second mistake. Plants packed too close together create humid conditions that encourage powdery mildew, early blight, and other fungal problems. Space them properly from the start.

Planting in the same spot year after year depletes soil and allows soil-borne diseases to build up. Rotate tomatoes to a different bed each season, or at least three years apart in the same location.

Frequently Asked Questions

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

Row covers do provide some frost protection, but they are not reliable enough for tomatoes. A hard freeze can still kill plants under covers, and tomatoes are sensitive to cold soil regardless of air protection. It is safer to wait until soil is warm and frost danger has truly passed.

What if my seedlings are already flowering when it is time to plant?

Pinch off the flowers before planting. Seedlings that flower indoors are stressed and will produce better if you remove flowers and let them focus on root and leaf growth after transplanting. The plant will flower again once it is established in the garden.

How do I know if soil is warm enough without a thermometer?

A rough guide: soil is usually warm enough when you can comfortably hold your bare hand in it for several seconds. A soil thermometer costs five to ten dollars and is more reliable. Many garden centres will test soil temperature for you if you bring a sample.

Can I plant tomatoes in containers instead of the ground?

Yes. Container tomatoes follow the same timing rules — plant after last frost and when soil temperature is adequate. Use a pot at least five gallons for determinate varieties and ten gallons for indeterminate types. Container soil warms faster than ground soil, so you may be able to plant a week or two earlier.

What happens if I plant tomatoes too close together?

Crowded plants have poor air circulation, which traps moisture and creates conditions for fungal diseases like early blight and powdery mildew. Leaves stay wet longer after rain or watering, and spores spread easily between plants. Proper spacing from the start prevents most fungal problems.