Starting seeds indoors
Start seeds indoors with correct timing, adequate light, and practices that prevent damping-off and transplant shock.
12 min · beginner
You will learn
- Calculate indoor sowing dates from frost dates and packet instructions
- Provide adequate light to prevent leggy seedlings
- Harden off transplants for two weeks before setting them outdoors
Timing your starts
Count backward from your transplant date using weeks listed on the seed packet, typically four to eight weeks for tomatoes and peppers. Starting too early produces leggy, root-bound plants that struggle after transplant. Starting too late means small plants that lag behind direct-sown neighbors. Write sowing dates on a calendar keyed to your last frost date.
Light requirements
Window light alone rarely provides enough intensity for stocky seedlings. University of Minnesota Extension recommends grow lights positioned two to four inches above foliage for 12 to 16 hours daily. Raise lights as plants grow to prevent stretching. Leggy seedlings with long internodes signal insufficient light.
Preventing damping-off
Damping-off is a fungal disease that collapses seedlings at the soil line. University of Minnesota Extension advises using sterile seed-starting mix, not garden soil. Water from below when possible, and avoid keeping media constantly saturated. Good air circulation and moderate temperatures reduce risk. Thin overcrowded flats promptly so stems do not stay wet against neighbors.
Hardening off before transplant
Plants grown indoors lack the toughness to handle sun and wind immediately. University of Minnesota Extension recommends hardening off for about two weeks before transplant by gradually increasing outdoor time and sun exposure. Begin in shade and bring plants in if frost threatens. Transplant on a cloudy day or late afternoon to reduce wilting stress.