Zone 1a
In USDA zone 1a the coldest night of an average winter reaches −60 to −55 °F (−51.1 to −48.3 °C). 5 ZIP codes (0.0% of all) are in this zone.
Frost dates vary within zone 1a
For the middle half of zone-1a ZIP codes the last spring frost falls between May 25 and May 28, and the first fall frost between Aug 26 and Aug 26. The zone measures winter cold, not season length: humid Eastern and dry Western towns in the same zone can be weeks apart. Use your ZIP code for a planting date.
States with zone 1a
Questions
What is the temperature range of zone 1a?
Zone 1a covers places where the coldest night of an average winter (the annual extreme minimum averaged over 1991–2020) is −60 to −55 °F, or −51.1 to −48.3 °C.
When is the last frost in zone 1a?
Across ZIP codes in zone 1a, the median last spring frost falls between May 25 and May 28 for the middle half of places. Zone alone doesn't set the frost date — check your ZIP code.
Which states have zone 1a?
Zone 1a occurs in 1 state; the most ZIP codes are in Alaska.
What can I grow in zone 1a?
Perennials, shrubs and trees labeled hardy to zone 1a or a lower (colder) number should survive a typical winter. Annual vegetables depend on frost dates rather than zone.
Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.