How to start seeds indoors (and actually get strong plants)
Timing, light, heat and hardening off: the steps that turn seeds into sturdy transplants.
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Starting your own seeds saves money and gets you varieties you'll never find at the garden center. Most failures come down to three things: starting too early, too little light, and skipping hardening off.
⭐ Top picks for this job
- Seedling heat matPeppers and tomatoes sprout in days instead of weeks.
- LED grow lightA windowsill isn't enough light in late winter.
- Seed trays with domesReusable 72-cell trays for starting dozens of plants.
Know your timing
Count back from your average last spring frost date. Peppers need about 8–10 weeks indoors, tomatoes 6–8 weeks, and fast crops like squash and cucumbers only 3–4 weeks. Starting too early gives you leggy plants that stall when they go outside. Our planting calendar works out the dates for you.
Use seed-starting mix, not garden soil
Seed-starting mix is fine, light and sterile, which helps prevent damping off, a fungus that makes seedlings collapse at the base.
Plant at the right depth
A good rule is to plant a seed about two to three times as deep as it is wide. Tiny seeds like lettuce barely need covering.
Give them warmth to sprout
Most vegetable seeds sprout fastest in soil around 70–85°F. A heat mat under the tray can cut pepper germination from weeks to days. Take it away once the seedlings are up.
Give them lots of light
This is the big one. A sunny window isn't enough in late winter. Hang an LED grow light 2–3 inches above the seedlings and run it 14–16 hours a day, raising it as they grow.
Water from the bottom
Pour water into the tray and let the cells soak it up. The soil surface stays drier, which also helps prevent damping off.
Harden them off
Seedlings raised indoors need 7–10 days to get used to sun and wind. Put them outside in shade for an hour or two, then a little longer and sunnier each day before transplanting.
Gear for this job
- Seedling heat mat: Peppers and tomatoes sprout in days instead of weeks.
- LED grow light: A windowsill isn't enough light in late winter.
- Seed trays with domes: Reusable 72-cell trays for starting dozens of plants.
- Seed-starting mix: Fine, sterile mix that prevents damping off.
- Grow light shelf: Start a whole garden's worth of plants in one corner.
- Plant labels: Know which tomato is which.