Frost Date Planner
Calculate transplant and seed-starting dates from your last spring frost date.
Returns timing for tomatoes, peppers, squash, herbs, and cool-season crops.
Frost date planning is the foundation of every vegetable garden calendar. The last spring frost date determines when tender plants can safely go outdoors; the first fall frost date tells you when to wrap up the season or bring plants inside. Getting these dates wrong can mean losing an entire crop overnight.
Core formulas:
Safe Outdoor Planting Date = Last Spring Frost Date + Weeks After Frost
Indoor Seed Start Date = Safe Outdoor Planting Date − Indoor Growing Weeks
Days to Harvest = Planting Date + Days to Maturity (from seed packet)
Growing Season Length = First Fall Frost Date − Last Spring Frost Date
Variable definitions:
- Last Spring Frost — the average date of the final below-32°F night in spring in your area
- First Fall Frost — the average date of the first below-32°F night in autumn
- Weeks After Frost — buffer time after the last frost before planting tender crops
- Indoor Growing Weeks — time seeds need indoors before they are large enough to transplant
Plant hardiness categories:
| Category | Examples | Planting Timing | Indoor Start |
|---|---|---|---|
| Hardy | Lettuce, peas, kale | 4 weeks before last frost | 6–8 weeks before planting |
| Semi-hardy | Broccoli, cabbage | 2 weeks before last frost | 6–8 weeks before planting |
| Tender | Tomatoes, peppers | 1–2 weeks after last frost | 6–8 weeks before planting |
| Very tender | Melons, basil | 3–4 weeks after last frost | 3–4 weeks before planting |
Worked example: Location: Chicago, Illinois. Last frost: May 15. First fall frost: October 10. Growing season = October 10 − May 15 = 148 days
For tomatoes (tender): Plant outdoors May 22–29 (1–2 weeks after frost). Start indoors = May 22 − 8 weeks = March 27
For peas (hardy): Plant outdoors April 17–May 1 (2–4 weeks before frost). Direct sow outdoors — no indoor start needed.
Frost probability tip: Frost dates are based on 30-year historical averages with a 50% probability of frost. For frost-sensitive crops, use the 10% probability date (usually 2–3 weeks later) as your safe planting target — local agricultural extension offices publish these tables by zip code.