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USDA Plant Hardiness Zone Map
USDA Miscellaneous Publication No. 1475, Issued January 1990
The 1998 "Web Version" of the USDA Plant Hardiness Zone Map
Go to the USDA Hardiness Zone Map
This map supersedes U.S. Department of Agriculture Miscellaneous Publication 814, "Plant Hardiness Zone Map," which was revised in 1965. This 1990 version shows in detail the lowest temperatures that can be expected each year in the United States, Canada, and Mexico. These temperatures are referred to as "average annual minimum temperatures" and are based on the lowest temperatures recorded for each of the years 1974 to 1986 in the United States and Canada and 1971 to 1984 in Mexico. The map shows 10 different zones, each of which represents an area of winter hardiness for the plants of agriculture and our natural landscape. It also introduces zone 11 to represent areas that have average annual minimum temperatures above 40 °F (4.4 °C) and that are therefore essentially frost free.
How to Use the New Map
Zones 2-10 in the map have been subdivided into light- and dark-colored sections (a and b) that represent 5 °F (2.8 °C) differences within the 10 °F (5.6 °C) zone. The light color of each zone represents the colder section; the dark color, the warmer section. Zone 11 represents any area where the average annual minimum temperature is above 40 °F (4.4 °C). The map shows 20 latitude and longitude lines. Areas above an arbitrary elevation are traditionally considered unsuitable for plant cropping and do not bear appropriate zone designations. There are also island zones that, because of elevation differences, are warmer or cooler than the surrounding areas and are given a different zone designation. Note that many large urban areas carry a warmer zone designation than the surrounding countryside. The map-contains as much detail as possible, considering the vast amount of data on which it is based and its size.
In using the map to select a suitable environment for a landscape plant, today's gardeners should keep in mind the following:
Additional Helpful Information
Hardiness Zones -- Details
- Stress Factors. We became aware of additional stresses to plants during the 1970's. Acid rain, gaseous and particulate pollution, security lighting, and toxic wastes, among many other stress factors, have significantly increased the potential for unsatisfactory performance of landscape plants. We need to document the tolerances of plants to these factors.
- New Plant Management Systems. New techniques of planting, transplanting, watering, fertilizing, and providing pest control measures have done much to increase the vigor of landscape plants. But used unwisely, these same measures can reduce plant hardiness.
- Artificial Environments. We became aware of additional stresses to plants during the 1970's. Acid rain, gaseous and particulate pollution, security lighting, and toxic wastes, among many other stress factors, have significantly increased the potential for unsatisfactory performance of landscape plants. We need to document the tolerances of plants to these factors.
Indicator Plant Examples --
by zone. -- Names of representative plants listed under the
coldest zones in which they normally succeed.
alphabetically. -- Cold hardiness ratings (zones) for selected
Miscellaneous Publication No. 1475. Issued January 1990
by Henry M. Cathey while Director, U.S. National Arboretum
formatted and prepared for the US National Arboretum web site by Ramon
Jordan, March 1998
National Arboretum, Agricultural Research Service, U.S. Department of Agriculture,
Washington, DC 20002.
Updated and edited,
by Yankee Gardener, February 2001
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