USDA Plant Hardiness Zone
Zone 1a Frost Dates & Planting Calendar
5 ZIP codes are in zone 1a in the ZIP-code listing of the 2023 USDA Plant Hardiness Zone Map; 0 of them have a frost-date page here.
- Zone
- 1a
- Coldest night, average
- -60 to -55°F
- Median Growing Season
- —
- ZIP codes in the listing
- 5
-51.1 to -48.3°C
What zone 1a actually tells you
The 2023 USDA Plant Hardiness Zone Map puts a place in zone 1a when the coldest night of the year averaged -60 to -55°F (-51.1 to -48.3°C) over 1991–2020. The zone says which perennials survive the winter, not when to plant in spring.
Frost dates answer the planting question, and they are read from the nearest NOAA station, not from the zone. The zone 1a ZIP codes here lie in 1 state; 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.
Zone 1a ZIP codes by state
Alaska
- 99720Allakaket
- 99788Chalkyitsik