Start seeds indoors 6 to 8 weeks before your last spring frost

The fastest way to grow tomatoes is to buy transplants from a garden center, but starting from seed gives you more varieties to choose from and costs less per plant. Fill a seed tray or small pots with seed-starting mix—not garden soil, which compacts and holds too much water. Plant one seed per cell, about a quarter inch deep, and keep the soil moist but not waterlogged.

Place the tray in a warm spot (70 to 75 degrees Fahrenheit is ideal) and cover it loosely with plastic wrap or a humidity dome to hold moisture. Seeds sprout in 5 to 10 days. Once they emerge, remove the cover and move the tray to a bright window or under grow lights positioned 2 to 3 inches above the seedlings. Without enough light, seedlings become leggy and weak.

Water from below by setting the tray in a shallow pan of water for 10 minutes, then draining it. This keeps the soil moist without wetting the leaves. When seedlings develop their first true leaves (the second set to appear), thin them so each has its own cell, or transplant them into individual small pots.

Key Takeaways

  • Seeds started indoors 6 to 8 weeks before your last frost date will be ready to plant outside when soil warms to 60 degrees Fahrenheit.
  • Seedlings need bright light for 14 to 16 hours daily and soil that stays moist but never soggy, or they will rot or become weak.
  • Harden off seedlings by gradually exposing them to outdoor conditions over 7 to 10 days before planting them in the garden.
  • Tomatoes need full sun (at least 6 to 8 hours daily), warm soil, and consistent water to produce fruit without cracking or rotting.
  • Determinate varieties grow to a fixed size and fruit all at once; indeterminate varieties grow tall and produce fruit until frost, so choose based on your space and canning plans.

Harden off seedlings before moving them outside

Seedlings grown indoors are tender and will wilt or die if moved directly into the garden. About 7 to 10 days before your last frost date, begin hardening them off—gradually exposing them to outdoor conditions. On day one, place seedlings in a sheltered, shaded spot outside for 1 to 2 hours. Bring them back inside.

Each day, increase their time outside and gradually move them into more direct sun. By day 7 or 8, they should spend the full day outside. If frost threatens, bring them in at night. This process toughens the leaves and stems so they can handle wind, direct sun, and temperature swings without shock.

Plant seedlings in warm soil with full sun and support

Wait until soil temperature reaches at least 60 degrees Fahrenheit and nighttime temperatures stay above 50 degrees—usually 1 to 2 weeks after your last frost date. Tomatoes planted in cold soil will sit dormant and may rot. Choose a spot that gets at least 6 to 8 hours of direct sun daily; more is better for fruit production and disease prevention.

Dig a hole slightly deeper than the seedling's root ball and bury the stem up to the first true leaves. Tomatoes can develop roots all along the buried stem, creating a stronger plant. Space plants 24 to 36 inches apart depending on the variety—determinate types stay compact, while indeterminate types grow tall and need more room.

Install a cage, stake, or trellis at planting time so you do not damage roots later. Determinate varieties (bush types) need a sturdy cage. Indeterminate varieties (vining types) do better on a tall stake or string trellis where you can tie the main stem as it grows and prune side shoots for better air flow.

Water deeply and consistently, especially once fruit sets

Tomatoes need 1 to 2 inches of water per week, delivered as deeply and infrequently as possible rather than daily sprinkles. Deep watering encourages roots to grow down into the soil. Water at the base of the plant in the early morning so leaves dry quickly and fungal diseases have less chance to take hold.

Once flowers appear and fruit begins to set, consistent water becomes critical. Irregular watering—dry spells followed by heavy rain or watering—causes fruit to crack, split, or develop blossom-end rot (a dark, sunken spot on the bottom of the fruit caused by calcium deficiency linked to inconsistent moisture). Mulch around plants with 2 to 3 inches of straw or shredded leaves to keep soil temperature steady and reduce water loss.

Prune indeterminate varieties and watch for common pests

Indeterminate tomatoes grow indefinitely and produce side shoots (suckers) that branch off between the main stem and leaf branches. Removing these suckers directs energy into fruit production and improves air flow, which reduces disease. Pinch off suckers when they are small—less than 2 inches long—by hand or with pruning shears. Leave determinate bush varieties unpruned; they are bred to produce a compact plant.

Watch for hornworms (large green caterpillars that eat leaves and fruit), spider mites (tiny pests that cause yellowing and webbing), and early blight (brown spots with concentric rings on lower leaves). Remove hornworms by hand or spray with spinosad, an organic insecticide. For spider mites, spray leaves with water or neem oil. For early blight, remove affected leaves and improve air flow by pruning lower branches and spacing plants farther apart.

Harvest fruit when it reaches full color

Tomatoes ripen from the inside out. Pick them when they reach full color for their variety—deep red, orange, yellow, or whatever the seed packet shows—and give slightly to gentle pressure. Fruit picked at this stage will be sweeter and have better flavor than fruit picked green and ripened indoors.

In late summer, when frost is 4 to 6 weeks away, pinch off new flower clusters so the plant puts energy into ripening existing fruit rather than starting new fruit that will not mature. If frost arrives before all fruit ripens, pick all remaining tomatoes—green or partially colored—and ripen them indoors on a windowsill or in a paper bag with a ripe banana, which releases ethylene gas and speeds ripening.

Choose determinate or indeterminate based on your goals

Determinate varieties (also called bush types) grow to a fixed height, usually 3 to 4 feet, and produce most of their fruit within a 2 to 3 week window. They need less pruning and are ideal for small spaces, containers, and canning because the harvest is concentrated. Common determinate varieties include Roma, San Marzano, and Mountain Magic.

Indeterminate varieties (vining types) grow continuously until frost and produce fruit throughout the season in smaller waves. They reach 6 feet or taller and need staking, tying, and pruning. They are better for fresh eating because you get tomatoes over many weeks. Common indeterminate varieties include Brandywine, Cherokee Purple, and Sungold.

Check the seed packet or plant label—it will say "determinate" or "indeterminate," or use the abbreviation "D" or "I." If you are new to growing tomatoes, determinate varieties are often easier because they require less maintenance and produce a predictable harvest.

Frequently Asked Questions

Can I plant tomatoes in a container?

Yes. Use a pot at least 5 gallons for determinate varieties and 10 gallons for indeterminate types. Fill it with potting mix, not garden soil. Container tomatoes dry out faster, so check soil moisture daily and water when the top inch feels dry. Feed every 2 to 3 weeks with a balanced fertilizer because nutrients leach out with frequent watering.

What causes blossom-end rot on tomatoes?

Blossom-end rot is a dark, sunken spot on the bottom of the fruit caused by calcium deficiency, which happens when soil moisture is inconsistent. Water deeply and regularly to keep soil evenly moist. Mulch to reduce water loss. If the problem appears mid-season, it usually stops once watering becomes consistent, though affected fruit cannot be saved.

Should I fertilize tomatoes?

Tomatoes benefit from fertilizer, but too much nitrogen produces leafy plants with few flowers and little fruit. Use a balanced fertilizer like 10-10-10 or a tomato-specific formula when planting, then feed every 3 to 4 weeks once flowers appear. Follow the package directions for amount. Avoid high-nitrogen lawn fertilizers.

Why are my tomato leaves turning yellow?

Yellow lower leaves are often normal as the plant matures and shades them. Remove them to improve air flow. Yellow leaves higher up can signal overwatering, poor drainage, nitrogen deficiency, or disease. Check soil moisture—it should feel like a wrung-out sponge. If soil is soggy, improve drainage. If it is dry, water more deeply.

Can I save seeds from my tomatoes?

Yes, but only from heirloom and open-pollinated varieties. Hybrid tomatoes (marked F1 on the seed packet) will not produce seeds that grow into plants like the parent. Scoop seeds and gel into a jar, add a little water, and let them ferment for 2 to 3 days to remove the gel coating. Rinse, dry on a paper towel for 2 to 3 weeks, and store in a cool, dry place.