grow · Grow

How to Start Seeds Indoors

Starting seeds indoors gives you a head start on the growing season and lets you grow varieties you can't find as seedlings. You need containers with drainage, seed starting mix, consistent warmth, and bright light. Most seeds germinate in 5-14 days and need 6-8 weeks indoors before transplanting outside after the last frost.

Ingredients

Step by step

  1. Choose your containers. Use seed trays, yogurt cups, or any container at least 2 inches deep with drainage holes. Clean containers with diluted bleach solution to prevent disease. Peat pots work well for plants that don't like root disturbance.
  2. Fill with seed starting mix. Use sterile seed starting mix, not garden soil or potting soil. These are too heavy and can harbor diseases. Fill containers to within half an inch of the rim and gently firm down. Water until evenly moist but not soaked.
  3. Plant seeds at proper depth. Plant seeds two to three times their diameter deep. Tiny seeds like lettuce barely need covering. Large seeds like beans go deeper. Drop 2-3 seeds per cell in case some don't germinate.
  4. Create warm conditions. Cover containers with plastic wrap or humidity domes to retain moisture. Place on a heat mat or warm surface like the top of a refrigerator. Most seeds need soil temperature between 65-75°F to germinate well.
  5. Provide light after germination. Remove plastic once seeds sprout. Place under grow lights 2-4 inches above seedlings for 12-16 hours daily, or in a south-facing window. Adjust light height as plants grow to prevent stretching.
  6. Water carefully. Water from the bottom by placing trays in shallow water, or use a spray bottle to avoid disturbing seedlings. Soil should stay consistently moist but never waterlogged. Seedlings are fragile and can damp off if conditions are too wet.
  7. Thin and transplant. When seedlings have their first true leaves, thin to the strongest one per cell. Cut weak ones with scissors rather than pulling. Transplant to larger pots when they outgrow their containers but before they become rootbound.

Tips & troubleshooting

Variations

Questions

When should I start seeds indoors?
Count backward from your last frost date. Most warm-season crops need 6-8 weeks indoors, cool-season crops need 4-6 weeks. Check seed packets for specific timing for each variety.
Why are my seedlings tall and weak?
They're stretching for light. Move lights closer or increase daily light exposure. Leggy seedlings can be saved by transplanting them deeper, burying part of the stem.
Can I use regular potting soil for starting seeds?
No, regular potting soil is too heavy and rich for seeds. Use sterile seed starting mix which drains better and has the right texture for germination.
How do I prevent damping off disease?
Use sterile containers and seed starting mix, provide good air circulation, avoid overwatering, and don't start seeds too early when indoor conditions are humid.
What if my seeds don't germinate?
Check if seeds are old, soil temperature is right, and moisture levels are consistent. Some seeds have low germination rates naturally. Plant extras to account for this.

Further reading