How to start vegetable seeds indoors

Starting seeds indoors gives warm-season crops a head start and costs far less than buying plants.

Reviewed October 2026

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What you need

• Trays or small pots with drainage holes, set in a waterproof tray so you can water from below.
• Sterile, lightweight seed-starting mix. Garden soil is too heavy and can carry disease.
• Lights. LED or fluorescent grow lights give sturdier seedlings than a windowsill, which is often drafty, chilly and dim. Lights around 5000K work well.
• A spray bottle for gentle watering.

When to start

Count back from your planting-out date. Peppers and eggplant need 8 to 10 weeks, tomatoes and basil 6 to 8, lettuce 4 to 5, and cucumbers and squash only 3 to 4. The planting calendar works out the dates once you enter your frost date.

Warmth, light and water

1. Keep seeds and seedlings at a steady 60 to 70°F. A basement or spare room is often better than a windowsill. A heat mat helps warmth-loving seeds like peppers sprout.
2. Keep lights just a few inches above the seedlings, and raise them as plants grow. Seedlings that stretch and lean are asking for more light.
3. Water gently and often enough to keep the mix moist but not soggy. Bottom-watering keeps the surface drier, which helps prevent seedlings rotting at the base.

Harden off before planting out

Seedlings raised indoors need to toughen up before they face sun and wind. Over 7 to 10 days, start with a couple of hours outside in the shade, then gradually increase their time outdoors and their exposure to direct sun. Don't skip this step: unhardened seedlings can scorch or stall.