Page Banner

United States Department of Agriculture

Agricultural Research Service

Related Topics


Location: Plant Introduction Research

2012 Annual Report

1a. Objectives (from AD-416):
The objective of this Specific Cooperative Agreement (hereinafter referred to as this Agreement) is to produce draft digital maps and grids (layers of map data) and associated data sets for the United States that use the best meteorological and technological information available, and which can be used to develop an approved, updated USDA-ARS Plant Hardiness Zone Map (PHZM) for the United States.

1b. Approach (from AD-416):
Using the PRISM climate modeling system, developed by the Cooperator, draft plant hardiness maps based on 1971-2000 temperature data for the conterminous U.S., Puerto Rico, Hawaii, and Alaska will be developed, accompanied by uncertainty analyses, variance maps, and separate maps for the periods 1971-1985 and 1986-2000. These layers of map data and data sets will be reviewed by the Technical Review Team, and their recommendations will be incorporated by the Coopertator into the final deliverables of this Agreement. At the completion of these tasks, it is the intent of USDA-ARS to use these deliverables to produce a final USDA-ARS PHZM that will fully acknowledge the contribution of the Cooperator in its development. Once the USDA-ARS PHZM map is produced, it is the intent of USDA-ARS to make it available to the public through a web portal. It is also the intent of ARS to allow the public to download the map and reproduce it without compensation in a wide variety of publications, such as journals, popular press magazines and product catalogues. The USDA-ARS PHZM may also be printed and sold by the National Technical Information Service, General Printing Office of the U.S. Government, or other Federal publishing offices. Therefore, ARS reserves a nonexclusive, irrevocable, royalty free license for the Federal government to publish the map or to authorize others to do so. Future applications of the USDA-ARS PHZM and the layers of map data contributing to it will be explored between USDA-ARS and the Cooperator, along with discussions about the creation of other digital climatological maps of interest to the USDA-ARS, such as solar radiation, evapotranspiration, and heat unit maps. If USDA-ARS and the Cooperator agree to develop mutually these future applications, this Agreement shall be modified to reflect additional objectives, tasks, deliverables and funding.

3. Progress Report:
The project has been fully accomplished with the web publication of the Plant Hardiness Zone Map and scientific journal publications regarding its development, the data layers, algorithms used, and analytical considerations. The U.S. Department of Agriculture released the new version of its Plant Hardiness Zone Map (PHZM) on January 25, 2012, updating a useful tool for gardeners and researchers for the first time since 1990 with greater accuracy and detail. Jointly developed with Oregon State University's (OSU) PRISM Climate Group, it is available online at 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. The 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 F) and 13 (60-70 degrees F). Each zone is a 10-degree Fahrenheit band, further divided into A and B 5-degree Fahrenheit zones. 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. Some of the changes in the zones, however, are a result of new, more sophisticated methods for mapping zones between weather stations. These include algorithms that considered for the first time such factors as changes in elevation, nearness to large bodies of water, and position on the terrain, such as valley bottoms and ridge tops. Also, the new map used temperature data from many more stations than did the 1990 map. These advances greatly improved the accuracy and detail of the map, especially in mountainous regions of the western United States. In some cases, advances resulted in changes to cooler, rather than warmer, zones. While about 80 million American gardeners, as well as those who grow and breed plants, are the largest users of the USDA Plant Hardiness Zone Map, researchers, educators, and nursery industry personnel need the hardiness zone information. In addition, the USDA Risk Management Agency uses the USDA plant hardiness zone designations to set some crop insurance standards. Scientists use the plant hardiness zones as a data layer in many research models such as modeling the spread of exotic weeds and insects.

4. Accomplishments

Last Modified: 2/23/2016
Footer Content Back to Top of Page