Seed Starting Date Calculator — When to Start Seeds Indoors by Last Frost

Your Last Frost Date & Plants

Last frost date (check your local extension office or use The Old Farmer's Almanac)

Select all plants you want to start indoors:

Harden off all transplants over 7–14 days before moving outdoors permanently. Start with 1 hour outside in shade, build up gradually.
Starting too early = leggy, root-bound seedlings that struggle after transplant. Bigger is not better with transplants.
Tomatoes and peppers need 65–75°F soil to germinate. Use a heat mat and aim for 6–8 weeks before transplant date, not frost date.
Celery, leeks, and onions have very slow germination — start 10–12 weeks early and be patient.
Marigolds and basil germinate quickly and don't need as much lead time. Start 4–6 weeks out.