Plant seedlings outdoors after the last frost date in your area, spacing them 24 to 36 inches apart and burying the stem deeper than it grew in the pot

Tomato seedlings are ready to move outside once they have at least two sets of true leaves (the leaves that look like actual tomato leaves, not the smooth oval seed leaves) and the soil temperature stays above 50°F at night. The safest timing is one to two weeks after your area's last spring frost date — you can find this date through your local cooperative extension office or by searching "[your city] last frost date." Planting too early into cold soil will stunt the seedling or kill it.

When you plant, bury the seedling deeper than it grew in its pot. Tomatoes develop roots all along the buried stem, which makes them stronger. Remove the lower leaves, then plant so only the top few leaves are above soil. Space seedlings 24 to 36 inches apart depending on the variety — check the seed packet or plant label for the mature width. Closer spacing works for determinate (bush) types; indeterminate (vining) types need more room.

Key Takeaways

  • Wait until soil temperature is consistently above 50°F at night and your area's last frost date has passed before moving seedlings outdoors.
  • Bury the seedling stem deeper than it was in the pot, removing lower leaves so only the top leaves show above ground.
  • Space seedlings 24 to 36 inches apart, with wider spacing for vining varieties that will sprawl across the garden.
  • Water seedlings thoroughly after planting and keep soil consistently moist for the first two weeks while roots establish.
  • Harden off seedlings by exposing them to outdoor conditions gradually over 7 to 10 days before permanent planting.

Hardening off seedlings before planting outside

Hardening off means gradually exposing seedlings to outdoor sun, wind, and temperature swings so they don't wilt or burn when planted. Start this process 7 to 10 days before your planned planting date. Place seedlings in a sheltered spot outdoors (against a wall, under a porch, or in a cold frame) for 2 to 3 hours on the first day, then bring them back inside.

Each day, increase outdoor time by 1 to 2 hours and move them into more direct sun. By day 7 or 8, seedlings should spend the full day outside. If nighttime temperatures drop below 50°F, bring them inside or cover them with a frost cloth. On the final day or two before planting, leave them out overnight if temperatures stay above 50°F. This toughens the stems and leaves so they handle wind and sun without shock.

Choosing a planting location and preparing the soil

Tomatoes need at least 6 to 8 hours of direct sun daily — more sun produces more fruit and better flavor. Choose a spot that gets morning sun, which dries dew and reduces disease. Avoid planting in the same spot where tomatoes, peppers, or potatoes grew in the past two years, because soil-borne diseases can linger.

Before planting, work compost or aged manure into the top 8 to 10 inches of soil. Tomatoes are heavy feeders and benefit from organic matter that holds moisture and nutrients. If your soil is very poor, mix in a balanced fertilizer (such as 5-10-10) at the rate listed on the package. Test your soil pH if possible — tomatoes prefer slightly acidic soil between 6.0 and 6.8, though they tolerate a wider range.

Planting depth and spacing for strong root systems

The single most important step is planting depth. Remove the seedling from its pot and pinch off the lowest leaves, leaving only the top 3 to 4 sets of leaves. Dig a hole deep enough so you can bury the seedling up to the lowest remaining leaves. The buried stem will sprout roots, creating a stronger root system that anchors the plant and absorbs more water and nutrients.

For spacing, measure from the center of one seedling to the center of the next. Determinate (bush) varieties can be 24 inches apart; indeterminate (vining) varieties need 30 to 36 inches. Crowding seedlings reduces air circulation, which invites fungal diseases like early blight. If you are planting in containers, use a pot at least 5 gallons for determinate types and 10 gallons for indeterminate types, and plant only one seedling per pot.

Watering and mulching after planting

Water seedlings thoroughly when ready after planting so soil settles around the roots and eliminates air pockets. For the first two weeks, keep soil consistently moist but not waterlogged — aim for moisture at the depth of your finger when you press into the soil. Once roots establish and new growth appears, you can water less frequently but more deeply, soaking the root zone once or twice weekly depending on rainfall and temperature.

explore 2 to 3 inches of mulch (straw, shredded leaves, or wood chips) around each seedling, keeping it 2 inches away from the stem. Mulch retains soil moisture, keeps roots cooler, and suppresses weeds. As the season progresses and seedlings grow, you may need to add support — stakes, cages, or strings — especially for indeterminate varieties that will grow tall and heavy with fruit.

Protecting seedlings from pests and weather stress

Young seedlings are vulnerable to cutworms, which sever stems at soil level. Create a barrier by placing a toilet paper tube or small cardboard collar around each seedling, pressing it 1 inch into the soil and extending 2 inches above. Remove the collar once the seedling is 4 to 6 inches tall and has hardened off.

If an unexpected cold snap or frost threatens after planting, cover seedlings with frost cloth, row covers, or even old sheets anchored at the corners. Remove the cover once temperatures rise above 50°F during the day. If seedlings show signs of stress — wilting, yellowing, or stunted growth — check soil moisture and temperature first, then look for pests or disease. Most stress in the first few weeks comes from cold soil, inconsistent watering, or insufficient hardening off.

Container planting for seedlings

If you are planting in containers rather than garden beds, use a pot with drainage holes and fill it with potting mix (not garden soil, which compacts in containers). A 5-gallon pot works for determinate varieties; indeterminate varieties do better in 10-gallon pots or larger. Plant the seedling at the same depth as you would in the ground — bury the stem up to the lowest leaves.

Container plants dry out faster than garden beds, so check soil moisture every 2 to 3 days during hot weather. Water until it drains from the bottom, then empty the saucer so roots do not sit in standing water. Container tomatoes benefit from a balanced fertilizer every 2 to 3 weeks once they start flowering, because frequent watering leaches nutrients from the limited soil volume.

Frequently Asked Questions

Can I plant seedlings deeper if they are tall and leggy?

Yes. Leggy seedlings (tall with long spaces between leaves) often result from insufficient light indoors. Bury them even deeper than normal, removing all but the top 2 to 3 sets of leaves. The extra buried stem will root and create a stronger plant, though it may take an extra week or two to recover from transplant stress.

What should I do if my seedlings wilt after planting?

Wilting usually means the soil is too dry or too cold. Check soil moisture by pressing your finger 2 inches into the soil — if it is dry, water thoroughly. If soil is moist but seedlings still wilt, the problem is likely cold soil or transplant shock. Wait a few days; most seedlings recover once roots establish. If wilting persists and soil is wet, the seedling may have root rot from waterlogging.

How long before seedlings start growing after planting?

Seedlings usually show new growth within 1 to 2 weeks, though growth is slow the first week as roots establish. If a seedling shows no new growth after three weeks, it may be struggling with cold soil, poor drainage, or pests. Check soil temperature and moisture, and inspect the stem and soil surface for cutworms or other damage.

Can I plant seedlings in a cold frame instead of hardening them off outdoors?

Yes. A cold frame (a box with a transparent lid) protects seedlings while exposing them to outdoor light and temperature fluctuations. Open the lid during warm days and close it at night for the first week, then leave it open during the day and closed at night for another week. This achieves hardening off while reducing wind damage and pest exposure.

What is the difference between determinate and indeterminate tomatoes for spacing?

Determinate (bush) tomatoes grow to a fixed height, usually 3 to 4 feet, and can be planted 24 inches apart. Indeterminate (vining) tomatoes grow continuously and can reach 6 to 10 feet, so they need 30 to 36 inches of space and benefit from more robust support. Check your seed packet or plant label to know which type you have.