Plant Hardiness Zone Finder

A plant hardiness zone is not an average winter temperature. It is the average annual extreme minimum temperature: the coldest night of each winter, averaged over 30 years. The 2023 USDA Plant Hardiness Zone Map, produced with Oregon State University's PRISM Climate Group, uses the 1991 to 2020 record from more than 13,000 weather stations.

Zones run in 10 F steps from zone 1 (below -50 F) to zone 13 (60 to 70 F), and each zone splits into 5 F half zones. Zone 7a covers 0 to 5 F and 7b covers 5 to 10 F, so a garden in 7b should expect its coldest night of a typical year to bottom out between 5 and 10 F. This finder uses the official ZIP code table from that map for the contiguous US, all 39,921 ZIP codes, and converts temperatures directly for everywhere else.

A perennial rated for zones 5 to 9 should survive a typical winter anywhere from 5a to 9b. Gardeners who want margin often pick plants hardy to one full zone colder than their own, especially for trees and shrubs that take years to replace. Zones only describe cold. They say nothing about summer heat, humidity or rainfall, which is why a zone 8 garden in Seattle and one in Dallas grow very different plants.

Microclimates matter more than the map at small scale. A south-facing wall, a city center or a spot near a large lake can run half a zone warmer, while low frost pockets and exposed hilltops run colder. Snow cover insulates roots, so a mulched bed survives colder air than bare soil would.