Starting seeds indoors
Timing, light and care for strong, stocky seedlings
Get the timing right
Find your local last spring frost date, then count back by the weeks each crop needs indoors. Seed packets give the number. Starting too early gives you tall, crowded plants long before it's warm enough outside.
- Peppers: about 8–10 weeks before the last frost.
- Tomatoes and eggplant: about 6–8 weeks.
- Broccoli, cabbage and cauliflower: about 4–6 weeks.
- Cucumbers, squash and melons: only 3–5 weeks, or sow them outside.
- Beans, corn, carrots, peas and radishes: sow these straight outside.
Gather your supplies
Any clean container works if it drains well and is at least 2 inches (5 cm) deep. Fill it with a fresh, sterile seed-starting mix, not garden soil or topsoil. Label every tray with the plant and the date.
Sow and wait
Moisten the mix before you sow. Plant seeds about twice as deep as they are wide, or as the packet says; tiny seeds are just pressed onto the surface.
Most vegetable seeds sprout best when the mix stays at 65–75°F (18–24°C). Cover the tray with clear plastic that doesn't touch the mix, and take it off as soon as sprouts appear.
Light is everything
A windowsill is seldom bright enough, and seedlings there grow tall and leggy. Hang grow lights 2–4 inches (5–10 cm) above the tops for 14 to 16 hours a day, raising them as plants grow.
Once they're up, grow seedlings a little cooler, about 65–70°F (18–21°C) by day and 55–60°F (13–16°C) at night, so they stay stocky.
Water, air and food
Steady care from here keeps seedlings healthy.
- Keep the mix evenly moist but never soggy. Soggy mix invites damping-off, which can wipe out a whole tray.
- Keep air moving and don't sow too thickly, which also helps prevent damping-off.
- Where several seeds came up in one cell, keep the strongest and snip off the rest at the soil.
- Most bagged mixes feed seedlings for 5 to 6 weeks. In a mix without fertilizer, start feeding at the first true leaves, following the label.
Before planting out
Seedlings raised indoors need hardening off before they go into the garden: a gradual introduction to sun, wind and cool nights. Our guide to hardening off has a day-by-day plan.
Related plant problems
Sources
- University of Maryland Extension: Starting Vegetable Seeds Indoors
- Clemson HGIC: Starting Seeds Indoors
- Clemson HGIC: FAQs about Starting Vegetable Seeds Indoors
- RHS: Damping off
General guidance, not a diagnosis. Written by PlantWiz in our own words from the sources above.