On 27 Oct 05 at 10:41, John Bryan wrote: > I wonder what your opinions are about the USDA Climate Zones. > I also wonder why such zones cannot be linked with our zip > codes, or postal zones. Would they not then be better defined? The USDA zones were devised to assess the winter hardiness of woody material and are based solely on average winter low temperatures. They are not, iow, *climate* zones. Climate involves a great deal more than just the winter low temperatures. For example, consider rainfall. Not only is the annual rainfall important, but also its distribution over the course of the year. We get abt 20" of rain a year here, but it mostly falls in the Dec-Feb period and our summers, though cool, are usually bone dry. The same amount of water spread out over the year would give entirely different growing conditions. Concentrate it in the summer, not the winter, and we might even be able to grow those touchy east Asian plants that, if they don't desiccate into nothingness in August, rot away in February. (Tricyrtis in Victoria? A complete failure in my former swamp.) Other factors: wind; exposure to sudden sharp outbusts of severe weather (as in Portland, Oregon when vileness swoops down the Columbia River gorge or here, where we get "arctic outflows" of seriously cold weather). Also summer heat units (degree-days) and length of growing season (frost-free period). And others. Even your exposure affects climate: the north side of a hill often has a very different climate from the south side. -- Rodger Whitlock Victoria, British Columbia, Canada Maritime Zone 8, a cool Mediterranean climate on beautiful Vancouver Island