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Most gardeners are familiar
with the U.S. Department of Agriculture's Plant
Hardiness Zone Map. This map was first published
in 1960 and updated in 1990. The map is based on
average annual minimum temperatures recorded throughout
North America. By using the map to find the zone
in which you live, you will be able to determine
what plants will "winter over" in your
garden, because they can withstand these average
minimum temperatures.
Although these zones are useful
as an indicator of a plant's likelihood for survival
in a given area, many factors, including soil type
and fertility, soil moisture and drainage, humidity,
and exposure to sun and wind determine a plant's
growth and success or failure in its enviroment.
Today, nearly all American reference books, nursery
catalogs, and gardening magazines describe plants
using USDA hardiness zones.
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