How to Start Tomato Seeds Indoors
Grow healthier plants and save money by starting tomatoes from seed
Step-by-Step Guide
Prepare Your Containers
Use cell trays, peat pots, or recycled containers with drainage holes. Fill with moistened seed-starting mix (not potting soil).
Plant Seeds
Plant 2-3 seeds per cell, 1/4 inch deep. Cover lightly and mist with water. Label varieties and planting date.
Provide Heat
Place on a heat mat or warm surface (70-80°F). Cover with a humidity dome or plastic wrap until seeds sprout.
Add Light Immediately
When seeds sprout, remove the dome and place under grow lights 2-4 inches above seedlings for 12-16 hours daily.
Thin Seedlings
When seedlings have 2 true leaves, thin to one plant per cell. Snip weak ones at soil level; don't pull.
Pot Up
When seedlings outgrow cells (usually 3-4 weeks), transplant to 4" pots. Bury stems up to lowest leaves - they'll grow more roots!
Harden Off
1-2 weeks before transplanting, gradually expose seedlings to outdoor conditions. Start with 1 hour of shade, increase daily.
Common Mistakes to Avoid
- • Starting too early: Leggy, weak seedlings that struggle at transplant
- • Not enough light: Causes stretched, weak stems
- • Overwatering: Leads to damping off disease
- • Skipping hardening off: Causes transplant shock
Frequently Asked Questions
When should I start tomato seeds indoors?
Start tomato seeds 6-8 weeks before your last expected frost date. In most areas, this means February-March for spring planting. Use our planting calendar for your specific zone.
How deep do you plant tomato seeds?
Plant tomato seeds 1/4 inch (6mm) deep. Cover lightly with seed starting mix and gently firm the soil. Keep moist but not waterlogged until germination.
Do tomato seeds need light to germinate?
No, tomato seeds germinate in darkness. However, once they sprout, they need 12-16 hours of bright light daily. Move to grow lights immediately after sprouting.
What temperature do tomato seeds need to germinate?
Tomato seeds germinate best at 70-80°F (21-27°C). Use a heat mat to maintain consistent warmth. Below 60°F, germination is slow or fails entirely.
Why are my tomato seedlings leggy?
Leggy seedlings result from insufficient light. Move lights closer (2-4 inches from tops) or increase light duration. Also ensure good air circulation and don't over-fertilize.