USDA Plant Hardiness Zone
Zone 3a Frost Dates & Planting Calendar
23 ZIP codes are in zone 3a in the ZIP-code listing of the 2023 USDA Plant Hardiness Zone Map; 3 of them have a frost-date page here.
- Zone
- 3a
- Coldest night, average
- -40 to -35°F
- Median Growing Season
- 113 days
- ZIP codes in the listing
- 23
-40.0 to -37.2°C
What zone 3a actually tells you
The 2023 USDA Plant Hardiness Zone Map puts a place in zone 3a when the coldest night of the year averaged -40 to -35°F (-40.0 to -37.2°C) over 1991–2020. The zone says which perennials survive the winter, not when to plant in spring.
Across the 3 NOAA stations behind zone 3a ZIP pages, the median 50% last spring frost is May 16 and the median first fall frost September 7; the last frost alone ranges from May 1 to May 17 from one station to another.
Frost dates answer the planting question, and they are read from the nearest NOAA station, not from the zone. The zone 3a ZIP codes here lie in 2 states; pick your own ZIP code below, or look up the zone of any ZIP code.
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.