Idaho Plant Hardiness Zones
Idaho’s towns run from zone 4b to zone 7b: the average coldest winter night is 9.8°F at Lewiston and -20.6°F at Victor.
Hardiness zones in Idaho
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.
- 3b
- 4a
- 4b
- 5a
- 5b
- 6a
- 6b
- 7a
- 7b
- 8a
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.
7b Zone 7b, 5 to 10°F 7 towns
7a Zone 7a, 0 to 5°F 32 towns
- Boise4.5°F
- Buhl0.4°F
- Caldwell3.8°F
- Coeur d'Alene1.6°F
- Eagle4.1°F
- Eagle Foothills2.9°F
- Emmett3.5°F
- Filer0.6°F
- Fruitland2.3°F
- Garden City4.6°F
- Genesee0.9°F
- Glenns Ferry1.2°F
- Greenleaf3.7°F
- Hagerman0.5°F
- Hidden Spring2.4°F
- Homedale3.1°F
- Horseshoe Bend3°F
- Kuna4.5°F
- Marsing4.2°F
- Melba4.7°F
- Meridian4.6°F
- Middleton3.9°F
- Mountain Home1.1°F
- Murphy3.5°F
- Nampa4.7°F
- New Plymouth2.3°F
- Notus3.4°F
- Parma2.9°F
- Payette2.7°F
- Star4.2°F
- Weiser1.9°F
- Wilder3.4°F
6b Zone 6b, -5 to 0°F 41 towns
- Athol-4.5°F
- Bonners Ferry-2.5°F
- Burley-4.6°F
- Clark Fork-2.6°F
- Cottonwood-3.7°F
- Dalton Gardens-0.7°F
- Deary-3.1°F
- Dover-2°F
- Gooding-2.4°F
- Grangeville-2.1°F
- Hansen-2°F
- Hauser-0.7°F
- Hayden-1.6°F
- Hayden Lake-1.4°F
- Hazelton-4°F
- Heyburn-4.7°F
- Jerome-1.5°F
- Kellogg-2°F
- Kimberly-1.1°F
- Kootenai-2.6°F
- Moscow-2.3°F
- Moyie Springs-2.1°F
- Mullan-3.8°F
- Nezperce-3.7°F
- Oakley-3.5°F
- Osburn-2.2°F
- Pinehurst-0.9°F
- Plummer-1.6°F
- Ponderay-2.3°F
- Post Falls-0.6°F
- Potlatch-2.5°F
- Priest River-4.5°F
- Rathdrum-1°F
- Saint Maries-0.5°F
- Sandpoint-2.1°F
- Shoshone-4.5°F
- Smelterville-0.8°F
- Troy-0.5°F
- Twin Falls-0.2°F
- Wallace-2.3°F
- Wendell-0.7°F
6a Zone 6a, -10 to -5°F 17 towns
- American Falls-8.7°F
- Arbon Valley-9.3°F
- Bellevue-9.7°F
- Chubbuck-8.3°F
- Council-7.3°F
- Fort Hall-9.9°F
- Franklin-8.8°F
- Hailey-8.8°F
- Idaho City-8.5°F
- Inkom-9.5°F
- Malad City-8.5°F
- Paul-5.4°F
- Pocatello-7.8°F
- Preston-8.6°F
- Rupert-6.4°F
- Spirit Lake-6°F
- Tyhee-8.7°F
5b Zone 5b, -15 to -10°F 23 towns
- Aberdeen-11.3°F
- Ammon-12.1°F
- Blackfoot-10.5°F
- Carey-10.8°F
- Cascade-14.9°F
- Challis-12.5°F
- Downey-11°F
- Dubois-14.2°F
- Groveland-10.5°F
- Idaho Falls-11.9°F
- Iona-12.8°F
- Ketchum-12.1°F
- Lincoln-12.7°F
- McCammon-10.4°F
- Menan-14.9°F
- Moreland-11°F
- Rigby-12.9°F
- Ririe-13.2°F
- Riverside-10.6°F
- Salmon-11.1°F
- Shelley-11.5°F
- Sun Valley-11.8°F
- Ucon-13.8°F
5a Zone 5a, -20 to -15°F 14 towns
- Arco-18°F
- Ashton-15.2°F
- Conda-18.3°F
- Driggs-19.8°F
- Fairfield-18.8°F
- Grace-15.3°F
- McCall-15.7°F
- Paris-18.3°F
- Rexburg-15.8°F
- Roberts-17.1°F
- Saint Anthony-17.4°F
- Soda Springs-18.5°F
- Sugar City-16.9°F
- Teton-17.4°F
4b Zone 4b, -25 to -20°F 2 towns
Counties
At the county’s center; a county with hills or a coast spans several zones.
| County | Zone at the center | Average coldest night |
|---|---|---|
| Ada County | 7a | 3.7°F |
| Adams County | 7a | 0.3°F |
| Bannock County | 5b | -10.1°F |
| Bear Lake County | 5a | -18.7°F |
| Benewah County | 6b | -1.8°F |
| Bingham County | 5b | -10.9°F |
| Blaine County | 6a | -8.1°F |
| Boise County | 6b | -2.9°F |
| Bonner County | 6b | -2.8°F |
| Bonneville County | 5b | -12°F |
| Boundary County | 6a | -7°F |
| Butte County | 6b | -4.9°F |
| Camas County | 6a | -7.6°F |
| Canyon County | 7a | 4.5°F |
| Caribou County | 5a | -19.4°F |
| Cassia County | 6b | -5°F |
| Clark County | 5b | -12.7°F |
| Clearwater County | 6b | -2.9°F |
| Custer County | 5a | -16.9°F |
| Elmore County | 6a | -7.5°F |
| Franklin County | 5b | -10.2°F |
| Fremont County | 5a | -18.8°F |
| Gem County | 7a | 3.7°F |
| Gooding County | 6b | -1.9°F |
| Idaho County | 5a | -16.4°F |
| Jefferson County | 5a | -19°F |
| Jerome County | 6b | -3.5°F |
| Kootenai County | 6b | -1.6°F |
| Latah County | 6b | -2.2°F |
| Lemhi County | 6a | -6.3°F |
| Lewis County | 6a | -5.2°F |
| Lincoln County | 6a | -8.6°F |
| Madison County | 5a | -17.2°F |
| Minidoka County | 6a | -7.8°F |
| Nez Perce County | 7a | 3.9°F |
| Oneida County | 6b | -1.9°F |
| Owyhee County | 6b | -4.1°F |
| Payette County | 7a | 2.2°F |
| Power County | 6a | -6°F |
| Shoshone County | 6b | -4.3°F |
| Teton County | 5a | -19.4°F |
| Twin Falls County | 6b | -3.2°F |
| Valley County | 5a | -15.5°F |
| Washington County | 6a | -7.4°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.
| Zone | Average coldest night | In 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 |
| 6b | -5 to 0°F | -20.6 to -17.8°C |
| 7a | 0 to 5°F | -17.8 to -15.0°C |
| 7b | 5 to 10°F | -15.0 to -12.2°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.