Planting Guide · February 2025 · 5 min read
Starting seeds indoors gives you a significant head start on the growing season and access to a much wider selection of varieties than the garden center offers. Proper timing, lighting, and temperature are the keys to growing stocky, healthy transplants. With a few basic supplies and good technique, anyone can produce high-quality seedlings at home.
The most common mistake in seed starting is starting too early, which produces leggy, root-bound transplants. Determine your last expected frost date, then count backward based on each crop's recommended indoor growing period.
Seedlings need 14 to 16 hours of bright light per day. A south-facing window is rarely sufficient; invest in fluorescent or LED grow lights positioned 2 to 4 inches above the plant tops. Raise the lights as seedlings grow to prevent stretching.
Use a sterile seed-starting mix rather than garden soil, which can harbor disease organisms. Most vegetable seeds germinate best at soil temperatures of 70 to 80 degrees Fahrenheit. A heat mat under the trays significantly speeds germination, especially for tomatoes and peppers.
Keep the soil mix consistently moist but never soggy. Overwatering is the primary cause of damping off, a fungal disease that kills seedlings at the soil line. Water from the bottom when possible, and ensure containers have drainage holes.
Begin feeding with a dilute liquid fertilizer (quarter strength) once seedlings develop their first true leaves. Increase to half strength as plants grow. Good air circulation from a small fan reduces disease and strengthens stems.
🌱 Plan your planting dates with our free tool:
Try the Planting CalculatorSeedlings grown indoors must be gradually acclimated to outdoor conditions over 7 to 10 days before transplanting. Start by placing them outdoors in a sheltered, shady spot for 2 to 3 hours, gradually increasing exposure to sun and wind each day.
Bring seedlings inside if temperatures drop below 45 degrees Fahrenheit at night. By the end of the hardening-off period, plants should be spending full days and nights outdoors and are ready for transplanting into the garden or field.