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The Plant Hardiness Zone Map
The United States Department of Agriculture Plant Hardiness Zone Map is a generalized map of the average annual minimum temperatures in the United States and Canada. Its purpose is to show where the minimum winter temperature is, on average, within the limits of a particular plant's tolerance to cold. ![]()
Using the Map Within a zone, temperatures, including winter minimums, vary with elevation, proximity to water, and with microclimatic features. For example, on the coldest night of the year, plants along a south-facing wall can remain 10 degrees F warmer than plants along a north-facing wall. There are, of course, many factors that determine a plant's suitability to a particular region, but the USDA Hardiness Zone Map is the best single indicator for determining where a particular plant can tolerate the winters.
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