Zones. Every zone on this site comes straight from the official 2023 USDA Plant Hardiness Zone Map ZIP code listings published by the PRISM Climate Group at Oregon State University, which produced the map with the USDA Agricultural Research Service. We use the data unaltered. This site is not the official USDA map; see planthardiness.ars.usda.gov for the official interactive map.
City and state names. ZIP code place names come from GeoNames postal code data, used under a Creative Commons Attribution 4.0 license (geonames.org). A city page lists every ZIP code GeoNames assigns to that city name, which can include PO box ZIP codes.
Plant guide. The hardiness ranges, light, water, size and bloom times in our plant guide are typical figures for each plant as published by university extension services and botanic garden plant records. A named variety can be hardier or taller than the species, so the tag on the plant you buy wins. Planting dates are worked out from each zone's median frost dates (NOAA 1991 to 2020 climate normals, the same dates shown on our zone pages): perennials and shrubs from two weeks before the last spring frost to six weeks after it, or six to ten weeks before the first fall frost; tender annuals from a week after the last frost; hardy annuals up to four weeks before it; spring bulbs from about four weeks before the first fall frost; vegetables by Purdue Extension's planting groups.
Background. Facts about the map come from the USDA Agricultural Research Service announcement of November 15, 2023.
Checked November 7, 2026.