Zone 1

USDA Zone Hardiness standards are based on the lowest average minimum temperatures for an area and are used by growers as a rough guide to select plants that are most likely to do well in their area.

Plants that are Zone 1 are known to be the most cold hardy for Interior Alaska, surviving extreme minimum temperatures of -60 to -50° F. This is not a guarantee of winter survival, but an indication of relative plant hardiness.

https://planthardiness.ars.usda.gov/PHZMWeb/#