California climate

California Plant Hardiness Zones

California’s towns run from zone 6a to zone 11a: the average coldest winter night is 41.8°F at Las Flores and -8.5°F at June Lake.

Hardiness zones in California

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 California, from zone 5a to zone 11a, with the state’s border drawn.
  • 5a
  • 5b
  • 6a
  • 6b
  • 7a
  • 7b
  • 8a
  • 8b
  • 9a
  • 9b
  • 10a
  • 10b
  • 11a

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.

11a Zone 11a, 40 to 45°F 9 towns

10b Zone 10b, 35 to 40°F 175 towns

10a Zone 10a, 30 to 35°F 278 towns

9b Zone 9b, 25 to 30°F 498 towns

9a Zone 9a, 20 to 25°F 156 towns

8b Zone 8b, 15 to 20°F 63 towns

8a Zone 8a, 10 to 15°F 21 towns

7b Zone 7b, 5 to 10°F 7 towns

7a Zone 7a, 0 to 5°F 16 towns

6b Zone 6b, -5 to 0°F 12 towns

6a Zone 6a, -10 to -5°F 5 towns

Counties

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

CountyZone at the centerAverage coldest night
Alameda County10a30.3°F
Alpine County6b-2°F
Amador County9a23.5°F
Butte County9b27.5°F
Calaveras County9a22.7°F
City and County of San Francisco10b36.7°F
Colusa County9b25.5°F
Contra Costa County9b29.4°F
Del Norte County8b19.8°F
El Dorado County8b19.6°F
Fresno County9b27.1°F
Glenn County9a24.6°F
Humboldt County9a24.7°F
Imperial County9b28.8°F
Inyo County8b16.5°F
Kern County9b28.4°F
Kings County9a24.9°F
Lake County9a24.5°F
Lassen County7a3.7°F
Los Angeles County10a33.9°F
Madera County9b26.3°F
Marin County9b28.9°F
Mariposa County8b19.4°F
Mendocino County9a21.7°F
Merced County9a23.7°F
Modoc County7a1.2°F
Mono County6b-2.5°F
Monterey County9a24.8°F
Napa County9b26.5°F
Nevada County8b17.9°F
Orange County10b35.1°F
Placer County9a22.2°F
Plumas County7b8.6°F
Riverside County9a24.5°F
Sacramento County9b26.6°F
San Benito County9b25.1°F
San Bernardino County9a24.3°F
San Diego County9b29.3°F
San Joaquin County9b25.6°F
San Luis Obispo County9a21.7°F
San Mateo County10a30.9°F
Santa Barbara County10a32.6°F
Santa Clara County10a30.3°F
Santa Cruz County9b27.6°F
Shasta County9a24.6°F
Sierra County7a4.4°F
Siskiyou County8a10.6°F
Solano County9b25.8°F
Sonoma County10a30°F
Stanislaus County9b26°F
Sutter County9b25.5°F
Tehama County9b25.1°F
Trinity County8a13.6°F
Tulare County9b25.6°F
Tuolumne County8a10.5°F
Ventura County9b29.6°F
Yolo County9b27.2°F
Yuba County9b27°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
6a-10 to -5°F-23.3 to -20.6°C
6b-5 to 0°F-20.6 to -17.8°C
7a0 to 5°F-17.8 to -15.0°C
7b5 to 10°F-15.0 to -12.2°C
8a10 to 15°F-12.2 to -9.4°C
8b15 to 20°F-9.4 to -6.7°C
9a20 to 25°F-6.7 to -3.9°C
9b25 to 30°F-3.9 to -1.1°C
10a30 to 35°F-1.1 to 1.7°C
10b35 to 40°F1.7 to 4.4°C
11a40 to 45°F4.4 to 7.2°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.