  Digitalseed IndexDigital ComposterWorldwide Gardener |
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Common Ground  Digital Gardener San Diego Gardener |
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Digitalseed IndexDigital ComposterWorldwide Gardener |
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Common Ground Digital Gardener San Diego Gardener |
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USDA Plant Hardiness ZonesSince hardiness or tolerance to cold extremes is a primary consideration for farming and gardening in much of the US, the United States Department of Agriculture (USDA) has, since 1960, maintained and published temperature data for the North American continent. Using this data, the continent was separated into eleven USDA Plant Hardiness Zones (often just called "USDA Zones"). The USDA Zones were determined by separating the continent into eleven zones based on 10 degree F differences in average annual minimum temperature. In 1990, the USDA Zone map was more finely divided into twenty zones separated by 5 degree F differences.
Shortcomings of the USDA Plant Hardiness ZonesCold tolerances are not the only environmental conditions that effect plant vitality. In fact, in much of California and the Southwestern United States (predominantly composed of USDA Zones 8-11), it often isn't even terribly significant. Other environmental requirements involve the amount and quality of sunlight, heat, water, soil pH, and of course nutrient availability. A better measure for western gardeners that takes into account some of these other conditions are the Generalized Western Plantclimate Zones.
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