When to Start Tomatoes Indoors by Zone
Start tomato seeds indoors about 6 weeks before your last spring frost. Use your zone or My Garden frost date, then harden off before transplant.
Published by ThriveThyme
tomato seed starting zones winter
When to Start Tomatoes Indoors by Zone
Start tomato seed 6 weeks before your last spring frost, then harden off and transplant about a week after that frost—not on a national average date.
Published draft 2026-09-29 Slug: when-to-start-tomatoes-indoors-by-zone Sources: New Bot seed-start v1 (a578c06)—tomato 6w before last frost, harden 14, transplantAfter 7; /api/seeds tomato soilTemp/depth/DTH; live seed-start calendar; existing indoor-start and September zone drafts for voice. Does not invent ZIP frost dates—use My Garden or Find My Zone. Catalog still has no indoorWeeks field.
When to Start Tomatoes Indoors
Count 6 weeks before your last spring frost. Set that frost in My Garden (or pick a USDA zone with Find My Zone), then open the live seed-start calendar to turn the lead time into calendar dates for your yard.
Full plant detail: Tomato. Trays and light: How to start seeds indoors. Hub: Winter.
Zones 5–9 Example
The method is the same in every zone. Only your last frost changes.
1. Set last spring frost in My Garden (or confirm zone with Find My Zone). 2. Count back 6 weeks—that is your indoor sow date for tomato. 3. Harden off for 14 days before you move plants to the bed (harden-off guide). 4. Transplant about 7 days after last frost, when nights and soil are ready for a warm-season crop.
Do not paste a ZIP’s frost date from memory into a national chart. Use My Garden or Find My Zone, then the seed-start calendar.
Catalog Notes (Tomato)
Catalog soil about 60–85 F; sow 1/4 inch; about 75 days to harvest from transplant timing in the catalog. Warm soil and strong light after sprouting keep seedlings stocky. Skip a heat mat once they are up if they stretch.
Next Steps
Set last frost in My Garden, open seed starting, sow tomato 6 weeks out, harden 14 days, and transplant about 7 days after last frost. Pair with pepper trays (8 weeks before last frost) if you want both warm-season crops in the same spring wave.