Regional Climate Guide
A USDA zone screens winter cold tolerance. Your region adds summer heat, rainfall, frost timing, wind, soil, and the length of the usable season.
Two yards can share a hardiness number while receiving different rain, summer heat, wind, and frost windows.
Mediterranean rainfall patterns and strong local microclimates make summer water, elevation, coast exposure, and fire conditions decisive.
California
Each full zone spans 10°F. Local a and b subzones divide that band into 5°F steps.
The number comes from average annual extreme minimum temperature, not an average winter day.
Trees, shrubs, and returning perennials need a winter band that matches their cold tolerance.
Summer heat, humidity, rainfall, drainage, and microclimates can still remove a plant from the shortlist.
Use the ranges below as regional planning windows. A local extension source gives the closer date for your address.
A long season can support repeated sowings. A short season needs fast varieties, transplants, or protection.
Watch local soil temperature and late frost risk before moving tender starts outside.
Heat, rainfall, and root-zone moisture decide whether a cold-hardy plant can stay healthy.
Finish establishment before the ground freezes and protect roots during temperature swings.
