Iowa climate

Iowa Plant Hardiness Zones

Iowa’s towns run from zone 4b to zone 6a: the average coldest winter night is -6.8°F at Keokuk and -21.8°F at Cresco.

Hardiness zones in Iowa

In USDA’s colors, neighboring states washed out. Zones follow elevation, coasts and cities down to half a mile. Drawn by WeatherOverTime from the USDA-ARS and Oregon State University PRISM Climate Group 2023 GIS data; this is not the official USDA Plant Hardiness Zone Map.

Map of the 2023 plant hardiness zones across Iowa, from zone 4b to zone 6a, with the state’s border drawn.
  • 4b
  • 5a
  • 5b
  • 6a

Open the live map with plant hardiness zones

Towns by zone

Each town’s 1991-2020 average annual extreme minimum at its center, read from the map’s 800 m grid. Warmest zone first.

6a Zone 6a, -10 to -5°F 14 towns

5b Zone 5b, -15 to -10°F 173 towns

5a Zone 5a, -20 to -15°F 266 towns

4b Zone 4b, -25 to -20°F 4 towns

Counties

At the county’s center; a county with hills or a coast spans several zones.

CountyZone at the centerAverage coldest night
Adair County5b-13.4°F
Adams County5b-13.6°F
Allamakee County5a-18.9°F
Appanoose County5b-11.5°F
Audubon County5a-15.6°F
Benton County5a-16.5°F
Black Hawk County5a-17.2°F
Boone County5a-15.4°F
Bremer County5a-18.4°F
Buchanan County5a-18.1°F
Buena Vista County5a-17.5°F
Butler County5a-17.1°F
Calhoun County5a-16.2°F
Carroll County5a-15.2°F
Cass County5a-15.1°F
Cedar County5a-15.5°F
Cerro Gordo County5a-18.6°F
Cherokee County5a-18.1°F
Chickasaw County5a-18.8°F
Clarke County5b-12.9°F
Clay County5a-18.9°F
Clayton County4b-20.4°F
Clinton County5a-15.6°F
Crawford County5a-15.1°F
Dallas County5b-14.6°F
Davis County5b-10.4°F
Decatur County5b-13.1°F
Delaware County5a-19.8°F
Des Moines County6a-10°F
Dickinson County5a-19°F
Dubuque County5a-17.7°F
Emmet County5a-18.3°F
Fayette County5a-19.9°F
Floyd County5a-18.3°F
Franklin County5a-17.4°F
Fremont County5b-11°F
Greene County5b-14.5°F
Grundy County5a-17.2°F
Guthrie County5a-18°F
Hamilton County5a-16.7°F
Hancock County5a-18.5°F
Hardin County5a-16.4°F
Harrison County5b-14.1°F
Henry County5b-10.6°F
Howard County4b-20.8°F
Humboldt County5a-17.4°F
Ida County5a-16.6°F
Iowa County5a-15.4°F
Jackson County5a-16.8°F
Jasper County5b-12.7°F
Jefferson County5b-11.1°F
Johnson County5b-12.8°F
Jones County5a-17.5°F
Keokuk County5b-12.2°F
Kossuth County5a-17.9°F
Lee County6a-7.8°F
Linn County5a-15.2°F
Louisa County5b-11.1°F
Lucas County5b-12.7°F
Lyon County5a-19.4°F
Madison County5b-14.2°F
Mahaska County5b-12.7°F
Marion County5b-11.8°F
Marshall County5a-15.7°F
Mills County5b-10.9°F
Mitchell County5a-18.9°F
Monona County5a-15.2°F
Monroe County5b-11.8°F
Montgomery County5b-14.6°F
Muscatine County5b-12.3°F
O'Brien County5a-18.9°F
Osceola County5a-20°F
Page County5b-13.3°F
Palo Alto County5a-17.7°F
Plymouth County5a-17.2°F
Pocahontas County5a-18.1°F
Polk County5b-13.3°F
Pottawattamie County5b-12.8°F
Poweshiek County5a-15.1°F
Ringgold County5b-13°F
Sac County5a-16.5°F
Scott County5b-13.3°F
Shelby County5b-14.2°F
Sioux County5a-19°F
Story County5b-14.8°F
Tama County5a-16.1°F
Taylor County5b-13.7°F
Union County5b-12.7°F
Van Buren County5b-10.4°F
Wapello County5b-10.9°F
Warren County5b-14.2°F
Washington County5b-12.3°F
Wayne County5b-12.6°F
Webster County5a-16.8°F
Winnebago County5a-19°F
Winneshiek County4b-20.6°F
Woodbury County5a-16.3°F
Worth County5a-19.6°F
Wright County5a-17.9°F

The zones

A plant hardiness zone is set by the average of each winter’s single coldest temperature, 1991 to 2020: zones are 10°F apart and each half zone, a and b, 5°F. It says how cold a winter night usually gets, not the coldest it has ever been, and nothing about summer heat, rain or soil. Plant labels give the coldest zone a perennial survives in.

ZoneAverage coldest nightIn Celsius
4b-25 to -20°F-31.7 to -28.9°C
5a-20 to -15°F-28.9 to -26.1°C
5b-15 to -10°F-26.1 to -23.3°C
6a-10 to -5°F-23.3 to -20.6°C

Sources

Hardiness zones: USDA Plant Hardiness Zone Map, 2023, Agricultural Research Service, U.S. Department of Agriculture, from the GIS data of the PRISM Climate Group, Oregon State University, which may be freely reproduced and redistributed. Drawn by WeatherOverTime from the USDA-ARS and Oregon State University PRISM Climate Group 2023 GIS data; this is not the official USDA Plant Hardiness Zone Map.