Extract seeds from a ripe tomato and dry them properly

You can grow new tomato plants from seeds inside a tomato you buy at the store or harvest from your garden. The process takes about two weeks of drying time, then another six to eight weeks before the seedlings are ready to move into soil outdoors. The key is removing the gel coating around each seed—this coating prevents germination, so you have to wash it away before the seeds will sprout.

Choose a fully ripe tomato. The tomato should be soft when you squeeze it gently, and the color should be deep red (or whatever the mature color is for that variety). Cut the tomato in half horizontally, across the middle rather than top to bottom. Squeeze the seeds and gel into a small bowl or cup—you'll get a pulpy mixture that looks like tomato juice with seeds floating in it.

Add a small amount of water to the bowl, just enough to cover the seeds by half an inch. Let this mixture sit at room temperature for two to three days. You'll see mold or a white film form on top—this is normal and actually helps break down the gel coating. Stir it once a day with a spoon.

Key Takeaways

  • Rinse seeds under running water in a fine strainer for two to three minutes to remove all gel coating, which blocks germination.
  • Spread cleaned seeds on a paper plate or coffee filter and let them dry completely in a warm, dry spot for 10 to 14 days before storing.
  • Plant dried seeds indoors six to eight weeks before your last spring frost, pressing them lightly into moist seed-starting mix and keeping soil warm.
  • Seeds need light to germinate, so cover them with only a thin layer of soil or leave them uncovered under grow lights or a sunny window.

Rinse and dry the seeds completely

After two to three days, pour the seed mixture into a fine-mesh strainer. Run cool water over the seeds while rubbing them gently with your finger to remove the gel coating. You'll feel the seeds become slippery as the gel washes away. Keep rinsing for two to three minutes until the seeds feel smooth and the water running through is clear, not cloudy.

Spread the clean seeds on a paper plate, coffee filter, or paper towel in a single layer. Do not use plastic—it traps moisture and can cause mold. Place the plate in a warm, dry spot with good air circulation: a windowsill, a shelf in a warm room, or near (but not directly on) a heating vent. Avoid direct sunlight during drying, as intense heat can damage the seeds.

The seeds should dry completely in 10 to 14 days. They're ready when they snap cleanly if you bend one—a fresh seed will bend without breaking. Once fully dry, store them in a paper envelope in a cool, dry place. A refrigerator works well. Properly dried seeds stay viable for three to four years.

Start seeds indoors six to eight weeks before the last frost

Tomato seeds need warmth and light to sprout. Start them indoors in late winter or early spring, timing it so seedlings are ready to move outside after the last frost date in your area. You can find your local frost date by searching "[your city] last spring frost date" online, or by asking at a local garden center.

Fill a seed tray, small pots, or even a yogurt cup with seed-starting mix—a light, sterile soil blend made for germination. Regular garden soil is too heavy and can rot seeds. Moisten the mix with water until it feels like a wrung-out sponge. Press one seed into the soil about one-quarter inch deep, or leave it on the surface and cover with just a dusting of mix. Tomato seeds need light to germinate, so they should not be buried deeply.

Place the tray or pots in a warm spot—ideally 70 to 80 degrees Fahrenheit. A heat mat under the tray speeds germination. Keep the soil moist but not waterlogged; check daily and mist with a spray bottle if the surface begins to dry. Seedlings should sprout in five to ten days.

Provide light and thin seedlings as they grow

Once seedlings emerge, they need strong light when ready. Place them under grow lights or in a very sunny south-facing window. Without enough light, seedlings become tall and spindly and won't grow into healthy plants. If using a window, rotate the tray daily so all seedlings get equal light.

When seedlings have two sets of true leaves—the second set that looks like actual tomato leaves, not the first rounded seed leaves—thin them out. If you planted multiple seeds in one pot, snip away the weaker seedlings with scissors, leaving the strongest one. This prevents crowding and competition for nutrients.

Keep the soil moist and the air temperature between 65 and 75 degrees during the day. Once seedlings are growing steadily, you can reduce watering slightly—the soil should dry out a bit between waterings to encourage strong roots. Feed seedlings with a diluted liquid fertilizer every two weeks.

Harden off seedlings before moving them outside

About two weeks before your last frost date, begin hardening off the seedlings. This means gradually exposing them to outdoor conditions so they adjust to wind, direct sun, and temperature changes. Start by placing the tray outside in a sheltered, shaded spot for one to two hours. Bring them back inside.

Each day, increase the time outside and gradually move them into more direct sunlight. By the end of one to two weeks, seedlings should spend the full day and night outside. Watch the weather forecast—if frost is predicted, bring them inside or cover them with a blanket.

Once the soil temperature reaches 60 degrees and nighttime temperatures stay above 50 degrees, the seedlings are ready to plant in the garden. Harden off seedlings even if you're moving them to a greenhouse or cold frame—the process prevents transplant shock and produces stronger plants.

Plant seedlings in the garden at the right depth

Dig a hole slightly deeper than the seedling's root ball. Tomato plants can be buried deeper than they grew in the pot—in fact, they should be. Bury the stem up to the lowest set of leaves. Roots will form all along the buried stem, creating a stronger root system. Gently firm the soil around the base and water well.

Space seedlings 24 to 36 inches apart, depending on the variety. Determinate (bush) tomatoes need less space; indeterminate (vining) varieties need more. Water deeply after planting and keep the soil consistently moist for the first two weeks while roots establish. Once plants are growing, water deeply but less frequently to encourage deep roots.

Common mistakes to avoid

The most common error is not removing the gel coating from seeds. Seeds with gel still attached will not sprout, no matter how long you wait. If you skip the fermentation step or don't rinse thoroughly, germination will be very poor or fail entirely.

Overwatering seedlings is the second major problem. Wet soil causes damping off, a fungal disease that kills seedlings at the soil line. The soil should be moist, not soggy. Water from below by setting pots in a tray of water rather than pouring from above, or water only when the surface begins to dry.

Starting seeds too early is also common. Seedlings started more than eight weeks before the last frost become overgrown and stressed indoors. They're harder to harden off and often don't transplant well. Stick to the six to eight week window for best results.

Frequently Asked Questions

Can I plant tomato seeds directly in the garden instead of starting them indoors?

Yes, but only in warm climates where the soil stays above 60 degrees for at least three months. In most regions, the growing season is too short. Starting indoors gives you a head start and produces fruit earlier in the season. Direct seeding works best in zones 9 and warmer.

What if my seedlings are tall and spindly?

This means they're not getting enough light. Move them closer to the light source or add a grow light. You can also bury the spindly stem deeper when transplanting—tomatoes will root along the buried stem and recover. In the future, provide light when ready after seedlings sprout.

Do seeds from hybrid tomatoes grow into the same tomato?

No. Seeds from hybrid tomatoes produce plants that are different from the parent plant—they may be smaller, a different color, or taste different. Seeds from heirloom or open-pollinated varieties will grow into plants that match the parent tomato. Check the seed packet or tomato label to see what type you have.

How long do tomato seeds stay viable if I store them?

Properly dried and stored seeds stay viable for three to four years. Store them in a paper envelope in a cool, dry place like a refrigerator or basement. Keep them away from moisture and heat. Write the variety and harvest date on the envelope so you know what you're planting.

Can I use seeds from a tomato that's been sitting in the refrigerator for weeks?

Yes, as long as the tomato hasn't molded or rotted. The seed viability doesn't change much during storage. However, very old tomatoes may have begun to break down internally, making it harder to extract clean seeds. Fresh tomatoes are easier to work with, but refrigerated ones will work.