The USDA Plant Hardiness Zone Map divides the country by how cold winters get. It is the standard gardeners and nurseries use to decide which perennial plants can survive the winter in a location.
What a zone measures
A zone is based on the average annual extreme minimum temperature: the coldest temperature of each winter, averaged over 30 years. The 2023 map uses 1991–2020 data. Each full zone covers 10°F and is split into an “a” half (colder) and a “b” half (warmer) of 5°F each. For example, zone 6a is −10 to −5°F and zone 6b is −5 to 0°F.
The 2023 update
The 2023 map replaced the 2012 edition. It was produced by the USDA Agricultural Research Service with Oregon State University’s PRISM Climate Group. Because it uses a newer 30-year period, many locations moved into a warmer half zone.
Zones vs. frost dates
Zones tell you what can survive your winter; frost dates tell you when to plant. A tomato is an annual in most of the country, so its zone rating doesn’t matter, but the last spring frost date does.
How we use the data
We use the 2023 map’s published ZIP code table, which lists one zone per ZIP code. Large ZIP codes in hilly areas can contain several zones, so treat the ZIP value as a guide. We don’t reproduce or alter the official map; for the interactive map, visit the USDA Plant Hardiness Zone Map.
Source: 2023 USDA Plant Hardiness Zone GIS datasets, PRISM Climate Group, Oregon State University.