From a USDA Announcement:
The U.S. Department of Agriculture (USDA) today released the new version of its Plant Hardiness Zone Map (PHZM), 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’sy (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 also have been included to ensure the map is readily accessible to those who lack broadband Internet access.
“This is the most sophisticated Plant Hardiness Zone Map yet for the United States,” said Catherine Woteki, USDA Under Secretary for Research, Education and Economics. “The increases in accuracy and detail that this map represents will be extremely useful for gardeners and researchers.”
Plant hardiness zone designations represent the average annual extreme minimum temperatures at a given location during a particular time period. They do not reflect the coldest it has ever been or ever will be at a specific location, but simply the average lowest winter temperature for the location over a specified time. Low temperature during the winter is a crucial factor in the survival of plants at specific locations.
The new version of the map includes 13 zones, with the addition for the first time of zones 12 (50-60 degrees Fahrenheit) and 13 (60-70 degrees Fahrenheit). Each zone is a 10-degree Fahrenheit band, further divided into 5-degree Fahrenheit zones “A” and “B”.
Direct to New Plant Hardiness Map