The 2012 USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 10-degree F zones.
The U.S. Department of Agriculture (USDA) released the new version of its Plant Hardiness Zone Map (PHZM) on January 25, updating a useful tool for gardeners and researchers for the first time since 1990 with greater accuracy and detail. The new map—jointly developed by USDA's Agricultural Research Service (ARS) and Oregon State University's (OSU) PRISM Climate Group—is available online at www.planthardiness.ars.usda.gov. ARS is the chief intramural scientific research agency of USDA.
For the first time, the new map offers a Geographic Information System (GIS)-based interactive format and is specifically designed to be Internet-friendly. The map website also incorporates a "find your zone by ZIP code" function. Static images of national, regional and state maps have also been included to ensure the map is readily accessible to those who lack broadband Internet access.
Compared to the 1990 version, zone boundaries in this edition of the map have shifted in many areas. The new map is generally one 5-degree Fahrenheit half-zone warmer than the previous map throughout much of the United States. This is mostly a result of using temperature data from a longer and more recent time period; the new map uses data measured at weather stations during the 30-year period 1976-2005. In contrast, the 1990 map was based on temperature data from only a 13-year period of 1974-1986.
No posters of the USDA Plant Hardiness Zone Map have been printed. But state, regional, and national images of the map can be downloaded and printed in a variety of sizes and resolutions. To view the map for the entire United States, go to http://planthardiness.ars.usda.gov/PHZMWeb/
Read the full press release from USDA regarding the release and development of the map at http://www.usda.gov/wps/portal/usda/usdahome?contentidonly=true&contentid=2012/01/0022.xml
For information about gardening contact your University of Arizona County Cooperative Extension office and ask to speak to a Master Gardener.