Start seeds indoors 6 to 8 weeks before your last spring frost, or direct sow them outdoors after soil warms to 60°F

Cherry tomato seeds germinate fastest when soil stays between 70°F and 80°F, which is why most home growers start them indoors under lights in late winter. You can also plant seeds directly into garden soil once the ground has warmed up in late spring, though indoor starting gives you a head start on the growing season. Either way, seeds sprout in 5 to 10 days under the right conditions, and seedlings are ready to move outdoors 6 to 8 weeks later.

The difference between the two methods comes down to timing and space. Indoor starting works best if you live where spring arrives late or if you want to harvest earlier in the summer. Direct sowing is simpler if you have garden space ready and don't mind waiting a few extra weeks for fruit. Both methods produce healthy plants—choose based on what you have room for and when you want to pick tomatoes.

Key Takeaways

  • Cherry tomato seeds need soil between 70°F and 80°F to sprout reliably, which takes 5 to 10 days.
  • Indoor seeds started 6 to 8 weeks before your last frost date will be ready to transplant outdoors when soil reaches 60°F.
  • Use seed-starting mix (not garden soil) indoors to prevent disease and give seeds the loose, moist environment they need.
  • Seedlings need 14 to 16 hours of light daily from a grow light or sunny window to stay short and sturdy instead of tall and leggy.
  • Harden off indoor seedlings by gradually exposing them to outdoor sun and wind over 7 to 10 days before planting them in the garden.

What you need for indoor seed starting

Gather a seed-starting container with drainage holes (recycled yogurt cups work, or buy seed trays), seed-starting mix (a sterile blend of peat moss or coco coir and perlite—not garden soil), cherry tomato seeds, and a way to keep soil warm and moist. A heat mat under your seed tray speeds germination by keeping soil at 75°F, though a warm shelf indoors works if you don't have one. You'll also need a grow light or a very sunny south-facing window; without strong light, seedlings stretch tall and weak.

For direct sowing outdoors, you need only the seeds, garden soil warmed to at least 60°F, and a spot that gets 6 to 8 hours of direct sun daily. If your soil is heavy clay, mix in compost or aged manure to loosen it first so seeds don't sit in waterlogged ground.

How to start seeds indoors step by step

Fill your container with seed-starting mix and water it until it's moist but not soggy—squeeze a handful and it should hold together without dripping. Press the mix gently to settle it, then make a small hole about 1/4 inch deep with your finger or a pencil. Drop one or two seeds into each hole and cover lightly with mix. Label the container with the variety and date.

Place the container on a heat mat or warm shelf and cover it loosely with a humidity dome or plastic wrap to keep moisture in. Check daily; the soil should stay moist like a wrung-out sponge. Once you see the first green sprout (usually 5 to 10 days), remove the cover when ready and move the container under a grow light positioned 2 to 3 inches above the seedlings.

Run the grow light for 14 to 16 hours daily and keep it close to the seedlings as they grow—raise it as they get taller so it stays 2 to 3 inches above the leaves. Without enough light, seedlings become tall, thin, and pale. Water from below by setting the container in a tray of water for 10 minutes, then letting it drain; this keeps the soil moist without wetting the leaves, which can cause fungal disease.

Thin seedlings when they have their first true leaves (the second set of leaves that look like actual tomato leaves, not the round seed leaves). Snip away the weaker seedling with scissors rather than pulling it out, which can disturb the roots of the one you're keeping. This gives the survivor room to grow stocky and strong.

Direct sowing seeds outdoors

Wait until soil temperature reaches at least 60°F—use a soil thermometer to check, or wait until nighttime temperatures stay above 50°F for a week. Prepare the planting area by loosening soil to 8 inches deep and mixing in 2 to 3 inches of compost if your soil is compacted or clay-heavy.

Make a shallow furrow about 1/4 inch deep and sprinkle seeds along it about 1 inch apart. Cover with soil, water gently, and keep the area moist until sprouts appear in 7 to 14 days. Once seedlings have two true leaves, thin them to 12 inches apart by snipping the weaker ones. This spacing gives each plant room for roots to spread and air to circulate around the stems.

Hardening off seedlings before transplanting

Indoor seedlings are tender and will wilt or burn if moved straight into full outdoor sun. Begin hardening off about 7 to 10 days before your last frost date by setting seedlings outside in a sheltered, shaded spot for 1 to 2 hours. Each day, gradually increase their time outside and move them into more sun—by day 7 or 8, they should handle full sun and outdoor wind for the whole day.

Watch the weather forecast; if frost threatens, bring seedlings back indoors. Once nighttime temperatures stay above 50°F and seedlings have been outside in full sun for at least 3 days, they're ready to plant in the garden.

Transplanting seedlings into the garden

Choose a spot with 6 to 8 hours of direct sun daily. Dig a hole slightly deeper than the seedling's root ball and set the plant in so the lowest leaves are just above soil level—cherry tomatoes can root along buried stems, which strengthens them. Space plants 18 to 24 inches apart so air flows between them and disease doesn't spread.

Water gently after planting and keep soil consistently moist (about 1 inch per week) for the first 2 to 3 weeks while roots establish. Once plants are growing steadily, you can back off to watering when the top inch of soil feels dry. Mulch around the base with 2 inches of straw or shredded leaves to keep soil temperature steady and reduce watering needs.

Common mistakes and how to avoid them

Using garden soil instead of seed-starting mix indoors compacts around seeds and traps moisture, causing rot before germination. Seed-starting mix is loose and sterile—it's worth buying. Planting seeds too deep means they exhaust their energy before reaching light; keep seeds 1/4 inch deep. Overwatering is the fastest way to kill seedlings—soil should be moist, not waterlogged.

Skipping the hardening-off step causes seedlings to collapse or turn purple when moved outdoors suddenly. The gradual transition takes only a week and makes the difference between plants that thrive and ones that struggle all season. Planting outdoors too early when soil is still cold slows germination and can cause seeds to rot; wait until soil reaches 60°F even if the air feels warm.

Frequently Asked Questions

Can I use a sunny windowsill instead of a grow light?

A south-facing window works if it gets at least 14 hours of bright, direct sun daily, but most home windows don't provide enough light. Seedlings grown in windows often become tall and leggy as they stretch toward the light. A grow light is inexpensive and gives you control over timing and intensity, so seedlings stay short and sturdy.

How long do cherry tomato seeds stay viable?

Cherry tomato seeds stay viable for 4 to 6 years when stored in a cool, dry place—a sealed jar in the refrigerator works well. Old seeds germinate more slowly and at lower rates, so if your seeds are more than 3 years old, plant a few extra to account for lower germination.

What if my seedlings are tall and spindly?

Tall, weak seedlings mean insufficient light or too much heat. Move the grow light closer (2 to 3 inches above the leaves), run it for 14 to 16 hours daily, and lower the temperature to 65°F to 70°F if possible. You can also bury the seedling deeper when transplanting—tomatoes root along buried stems and will develop a stronger root system.

Do I need to fertilize seedlings?

Seed-starting mix contains few nutrients, so seedlings benefit from a diluted fertilizer once they have their first true leaves. Use a balanced liquid fertilizer at half strength every 2 weeks, or switch to a richer mix when seedlings are 4 to 6 weeks old. Stop fertilizing a week before transplanting outdoors so plants aren't too soft.

Can I save seeds from my cherry tomatoes?

Yes, but only from open-pollinated or heirloom varieties—seeds from hybrid cherry tomatoes won't grow plants identical to the parent. Scoop seeds and gel into a cup, 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, then store in a cool, dry place.