http://www.sunset.com/sunset/garden/article/0,20633,845227,00.html

ZONE 1. Coldest Winters in the West and Western Prairie States
Growing season: early June through Aug., but with some variation—the longest seasons are usually found near this zone’s large bodies of water. Frost can come any night of the year. Winters are snowy and intensely cold, due to latitude, elevation, and/or influence of continental air mass. There’s some summer rainfall.

ZONE 2. Second-coldest Western Climate
Growing season: early May through Sept. Winters are cold (lows run from -3 degrees to -34 degrees F/-19 degrees to -37 degrees C), but less so than in Zone 1. In northern and interior areas, lower elevations fall into Zone 2, higher areas into Zone 1.

ZONE 3. West’s Mildest High-elevation and Interior Regions
Growing season: early May to late Sept.—shorter than in Zone 2, but offset by milder winters (lows from 13 degrees to -24 degrees F/-11 degrees to -31 degrees C). This is fine territory for plants needing winter chill and dry, hot summers.

ZONE 5. Ocean-influenced Northwest Coast and Puget Sound
Growing season: mid-April to Nov., typically with cool temperatures throughout. Less rain falls here than in Zone 4; winter lows range from 28 degrees to 1 degree F/-2 degrees to -17 degrees C. This “English garden” climate is ideal for rhododendrons and many rock garden plants.

ZONE 6. Oregon’s Willamette Valley
Growing season: mid-Mar. to mid-Nov., with somewhat warmer temperatures than in Zone 5. Ocean influence keeps winter lows about the same as in Zone 5. Climate suits all but tender plants and those needing hot or dry summers.

ZONE 7. Oregon’s Rogue River Valley, California’s High Foothills
Growing season: May to early Oct. Summers are hot and dry; typical winter lows run from 23 degrees to 9 degrees F/-5 degrees to -13 degrees C. The summer-winter contrast suits plants that need dry, hot summers and moist, only moderately cold winters.

ZONE 17. Oceanside Northern and Central California and Southernmost Oregon
Growing season: late Feb. to early Dec. Coolness and fog are hallmarks; summer highs seldom top 75 degrees F/24 degrees C, while winter lows run from 36 degrees to 23 degrees F/2 degrees to -5 degrees C. Heat-loving plants disappoint or dwindle here.