Zone 1b
In USDA zone 1b the coldest night of an average winter reaches −55 to −50 °F (−48.3 to −45.6 °C). 11 ZIP codes (0.0% of all) are in this zone.
Frost dates vary within zone 1b
For the middle half of zone-1b ZIP codes the last spring frost falls between May 22 and May 29, and the first fall frost between Aug 24 and Aug 28. 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 1b
← Zone 1a (colder)Zone 2a (warmer) →
Questions
What is the temperature range of zone 1b?
Zone 1b covers places where the coldest night of an average winter (the annual extreme minimum averaged over 1991–2020) is −55 to −50 °F, or −48.3 to −45.6 °C.
When is the last frost in zone 1b?
Across ZIP codes in zone 1b, the median last spring frost falls between May 22 and May 29 for the middle half of places. Zone alone doesn't set the frost date — check your ZIP code.
Which states have zone 1b?
Zone 1b occurs in 1 state; the most ZIP codes are in Alaska.
What can I grow in zone 1b?
Perennials, shrubs and trees labeled hardy to zone 1b 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.