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Generalized Western Plantclimate Zones
(Sunset Zones)
Because of the shortcomings of USDA Zones, most Western US gardeners and farmers use the so-called "Sunset Zones." The Sunset Zones (or more accurately, the Generalized Western Plantclimate Zones) are based on and adapted from the California Plantclimates developed by the University of California Cooperative Extension. These are often called Sunset Zones after the Sunset New Western Garden Book (Lane Publishing Co.) which popularized their usage. Four factors combine to make up the Western Plantclimate Zones:
- Latitude
(Effects day-length, average temparature, and severity and length of winter),
- Elevation
(Effects night temperatures and severity and length of winter),
- Ocean vs. continental air mass influence
(Effects severity of weather fluctuations and influences seasonal rainfall patterns; Major criteria is distance from the ocean and presence of mountain and hill barriers),
- Local terrain topology
(Effects the movement of cold air; Cold air is heavier than warm air; Hillsides and tilted valley floors which allow easy drainage of cold air are called thermal belts; Lowlands, valley centers, and river bottoms which tend to collect and trap the cold air are called cold-air basins; Above the thermal belts, winter temperatures can be even lower than in the cold-air basins)
Note: Unless otherwise noted, all zone references on this site shall refer to the Generalized Western Plantclimate Zones.
Shortcomings of the Plantclimate Zones
Local climatic variations caused by terrain topology and the presence of man-made structures are often significant but would be terribly impractical to document or map in any useful way. Serious gardeners use the local Plantclimate Zone designation as a starting point to help determine the local neighborhood microclimates and the microclimatic variations within their own backyards.
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Digitalseed Index
