When to Start Tomatoes Indoors
Perfect timing for strong transplants
Quick Answer
Start tomato seeds indoors 6-8 weeks before your last frost date. This gives seedlings enough time to develop strong roots and stems while avoiding overgrown, leggy plants. Transplant outdoors 1-2 weeks after last frost when soil is warm.
Seed Starting Timeline by Zone
| Zone | Last Frost | Start Seeds | Transplant |
|---|---|---|---|
| Zone 4 | May 15-30 | March 15-April 1 | May 25-June 10 |
| Zone 5 | April 30-May 15 | March 1-15 | May 10-25 |
| Zone 6 | April 15-30 | Feb 15-March 1 | April 25-May 10 |
| Zone 7 | April 1-15 | Feb 1-15 | April 10-25 |
| Zone 8 | March 15-30 | Jan 15-Feb 1 | March 25-April 10 |
Frequently Asked Questions
What happens if I start tomato seeds too early?
Starting too early creates leggy, root-bound seedlings that struggle after transplanting. Overgrown transplants are stressed and take longer to produce fruit. Stick to 6-8 weeks before transplant date for best results.
What temperature do tomato seeds need to germinate?
Tomato seeds germinate best at 70-85°F soil temperature. Use a heat mat to maintain consistent warmth. At optimal temperatures, seeds germinate in 5-10 days. Below 60°F, germination is slow and spotty.
Do tomato seedlings need light immediately?
Yes! Once seeds sprout, they need 14-16 hours of strong light daily to prevent legginess. Use grow lights positioned 2-4 inches above seedlings. A sunny south window may work but often isn't bright enough.
When should I transplant tomato seedlings to larger pots?
Transplant to 4-inch pots when seedlings have 2-3 sets of true leaves, typically 3-4 weeks after germination. Bury stems up to the first leaves - tomatoes develop roots along buried stems, making stronger plants.