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| USDA Plant Hardiness Zone | |
|---|---|
| Name | USDA Plant Hardiness Zone |
| Established | 1960s |
| Agency | United States Department of Agriculture |
| Purpose | Determining plant cold tolerance |
USDA Plant Hardiness Zone is a horticultural standard used to indicate which plants are most likely to thrive at a location based on minimum winter temperatures. It is maintained by the United States Department of Agriculture and used widely across the United States for gardening, landscaping, agriculture, and nursery trade. The system informs decisions by connecting climatic data to plant cold hardiness, influencing practice in botanical gardens, arboreta, and commercial nurseries.
The system divides the contiguous United States, Alaska, Hawaii, and territories into numbered zones based on average annual extreme minimum temperatures; related mapping efforts intersect with work by the National Oceanic and Atmospheric Administration, National Climatic Data Center, and regional offices of the United States Department of Agriculture. Landscape architects, extension services at institutions like the University of California, Davis and Texas A&M University rely on zone classifications alongside resources from the Smithsonian Institution and the United States Botanic Garden. Professional societies such as the American Society of Landscape Architects and the Royal Horticultural Society (for comparison) reference analogous data when advising plant selection or conservation. The zones are often cited in publications by the Missouri Botanical Garden, Brooklyn Botanic Garden, and plant societies including the American Rhododendron Society.
Origins trace to mid-20th century climatology and agricultural extension work influenced by agencies including the Soil Conservation Service and the Forest Service; the first widely distributed zone map appeared in the 1960s under the United States Department of Agriculture. Key updates have been informed by datasets from the National Weather Service, analyses at the National Center for Atmospheric Research, and climate researchers associated with NASA and the Intergovernmental Panel on Climate Change. The map’s development intersected with botanical research at the New York Botanical Garden, breeding programs at institutions like Iowa State University and Cornell University, and policy discussions involving the Environmental Protection Agency and state agricultural experiment stations.
Zones are computed from historical temperature records compiled by the National Climatic Data Center and gridded with methods developed by climate scientists at organizations such as the Princeton University geosciences group and the University Corporation for Atmospheric Research. The USDA map uses 10°F banding increments for primary zone numbers and 5°F subzones (a/b) reflecting average annual extreme minima; mapping techniques draw on interpolation methods used by the US Geological Survey and climatological mapping by the NOAA National Centers for Environmental Information. The 2012 revision incorporated modern digital elevation models from the United States Geological Survey and climate normals coordinated with the World Meteorological Organization standards. Visual and GIS dissemination involves platforms maintained by the National Agricultural Library and cooperative extension networks at land-grant universities such as Pennsylvania State University.
Nurseries, botanical institutions like the Missouri Botanical Garden and public gardens including the United States Botanic Garden use zones to label plant hardiness for consumers and professionals. Extension publications from University of Florida IFAS, Oregon State University, and Michigan State University integrate zone data into pest management, cultivar selection, and production scheduling. Landscape architects collaborating with the American Society of Landscape Architects and urban foresters from agencies like the United States Forest Service apply zone information for species selection in urban forestry programs and restoration projects overseen by organizations such as the National Park Service and The Nature Conservancy.
Critics including climatologists at Columbia University and ecologists at Duke University note the zone system emphasizes minimum temperature but neglects factors like heat stress, precipitation patterns, growing season length, microclimates, and soil conditions emphasized in work by the Natural Resources Conservation Service and researchers at the Smithsonian Tropical Research Institute. Agronomists at Rutgers University and plant physiologists at University of California, Davis highlight that reliance on zones can mislead gardeners regarding humidity-sensitive species or those affected by winter rainfall patterns studied by the Scripps Institution of Oceanography. Conservation biologists at University of Michigan and Yale University point to limitations for assisted migration and climate adaptation planning cited in reports by the Intergovernmental Panel on Climate Change.
Major revisions occurred in 1990 and 2012, driven by updated climate normals and improved spatial interpolation methods contributed by scientists at NOAA and academic partners including University of Washington and Colorado State University. Ongoing updates incorporate datasets from the National Centers for Environmental Information and climate monitoring by NASA Earth Science programs; policy and outreach for revisions have engaged stakeholders such as state extension services, botanical gardens like the New York Botanical Garden, and professional societies including the American Horticultural Society.
Comparable frameworks include the Royal Horticultural Society’s hardiness ratings, the Canadian Plant Hardiness Zone system maintained by Natural Resources Canada, and bioclimatic classification systems developed by researchers at the European Environment Agency and the Intergovernmental Panel on Climate Change. Alternative metrics that address criticisms include heat-zone mapping promoted by institutions like the Arid Lands Information Center and multi-factor indices used in studies from ETH Zurich, CSIRO, and Commonwealth Scientific and Industrial Research Organisation for Australia. Botanical gardens such as Kew Gardens and research centers at Max Planck Society institutions contribute comparative studies that guide international planting and conservation strategies.
Category:Plant hardiness