Destroy the weak seedlings by cutting them off with a razor blade. Short, stocky, dark green seedlings are the best quality transplants. For best results, grow seedlings under fluorescent lights. The fluorescent lights should be no more than 4 to 6 inches above the plants. They should be lit 12 to 16 hours per day.
Plants grown in a window often become tall and spindly because of inadequate light.
Thoroughly water the seedlings when the soil surface becomes dry to the touch. Fertilize weekly with a one-quarter strength houseplant fertilizer. Finally, harden or condition the seedlings outdoors for several days before planting them into the garden. Iowa State University , Ames, Iowa. This information subject to a usage policy .