USDA Plant Hardiness Zone
Zone 4b Frost Dates & Planting Calendar
1,138 ZIP codes across 17 states fall in zone 4b.
- Zone
- 4b
- Average Annual Low
- -25 to -20°F
- Typical Growing Season
- 136 days
- ZIP Codes
- 1,138
What zone 4b actually tells you
A hardiness zone describes one thing: the average coldest night of the year, which in zone 4b falls between -25 to -20°F. It answers whether a perennial will survive the winter — not when to plant in spring.
Frost dates answer the planting question, and they vary widely inside a single zone. Zone 4b spans 17 states, and a coastal ZIP can differ from an inland one by three weeks despite sharing the zone. Pick your own ZIP code below rather than planting by zone alone.