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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
When using the map to locate plants that will grow in your area there are some factors to be aware of. Some years the temperature may fall below the average minimum for a particular zone, and, of course, it is such extreme low temperatures, not averages, that kill sensitive plants.

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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