United States Department of Agriculture Plant Hardiness Zone Map

United States Department of Agriculture Plant Hardiness Zone Map
Name	United States Department of Agriculture Plant Hardiness Zone Map
Caption	2012 USDA Plant Hardiness Zone Map
Jurisdiction	United States
Agency	United States Department of Agriculture
Formed	1960
Website	USDA Plant Hardiness

United States Department of Agriculture Plant Hardiness Zone Map is a cartographic product produced by the United States Department of Agriculture to designate climatic zones across the United States based on average annual minimum winter temperatures. Developed for horticultural and agricultural use, the map influences planting recommendations, nursery labeling, landscape planning, and botanical research across federal and state institutions. It connects to a lineage of climatological and botanical projects involving national laboratories, universities, and scientific societies.

History and development

The map traces origins to early 20th-century work by the United States Department of Agriculture and contributions from scientists at the Smithsonian Institution, United States Weather Bureau, and researchers affiliated with the University of Minnesota, Iowa State University, Cornell University, University of California, Davis, and Texas A&M University. The original 1960 map synthesized data and guidance from regional horticulturalists, extension services such as the Cooperative Extension Service and botanical gardens including the United States Botanic Garden and New York Botanical Garden. Subsequent iterations incorporated efforts by climatologists at the National Oceanic and Atmospheric Administration and the National Weather Service, with academic input from institutions like Harvard University and University of Washington. The map’s dissemination involved partnerships with professional organizations such as the American Society for Horticultural Science, American Nursery & Landscape Association, and the Royal Horticultural Society for comparative work.

Methodology and data sources

Methodology for the map has relied on temperature observations from the National Climatic Data Center, station networks maintained by the National Oceanic and Atmospheric Administration, and gridded climate products produced by research groups at Princeton University and the National Center for Atmospheric Research. Data processing has employed spatial interpolation methods used in projects at the Lawrence Berkeley National Laboratory and algorithms developed by researchers at the Massachusetts Institute of Technology, Stanford University, and University of Illinois Urbana-Champaign. Historical climate normals and extremes came from archives at the Library of Congress and datasets curated by the National Archives and Records Administration and NOAA Paleoclimatology Program. The 2012 update incorporated high-resolution temperature grids produced with guidance from the Oak Ridge National Laboratory and mapping expertise informed by the United States Geological Survey.

Zone definitions and map interpretation

Zones are defined by 10 °F (5.6 °C) increments of average annual extreme minimum temperature, with subzones "a" and "b" for finer discrimination, mirroring classification practices used by botanical institutions such as the Royal Botanical Gardens, Kew and research gardens at the Missouri Botanical Garden. Interpreting the map often involves cross-referencing with plant hardiness lists maintained by the United States National Arboretum, seed companies like Burpee Seeds, and university extension catalogs from Pennsylvania State University Extension and University of Florida IFAS Extension. Horticulturists and landscape architects from firms registered with the American Society of Landscape Architects use the zone classifications alongside phenological data from networks like the USA National Phenology Network and observational records from the Audubon Society.

Updates and revisions

Major revisions occurred in 1990 and 2012, with the latter relying on 1976–2005 temperature normals and digital mapping techniques advanced by teams at Michigan State University and the University of California, Berkeley. Updates have been coordinated with federal entities including the Environmental Protection Agency for climatological context and the Department of Energy for modeling input, while international comparisons involved agencies such as Environment Canada and research centers like the Met Office in the United Kingdom. Ongoing revision efforts draw on climate modeling expertise at Columbia University’s Lamont–Doherty Earth Observatory and the Scripps Institution of Oceanography.

Criticisms and limitations

Critiques have come from scholars at Yale University, University of Colorado Boulder, and Duke University noting that reliance on historical normals can lag shifting climates documented by the Intergovernmental Panel on Climate Change and modeled by groups at the National Center for Atmospheric Research and the Geophysical Fluid Dynamics Laboratory. Limitations include coarse resolution for microclimates emphasized by urban planners in New York City and researchers at the USDA Forest Service, and inadequate representation of factors like snow cover, soil temperature, and heat islands studied by teams at the Urban Climate Lab at CUNY. Legal and policy stakeholders in agencies such as the Fish and Wildlife Service and the National Park Service have also raised concerns about applying static zones to dynamic restoration and conservation projects.

Applications and impact

The map is used by nurseries such as Monrovia Growers, seed companies like Johnny's Selected Seeds, and landscape firms working with the Trust for Public Land and the National Arbor Day Foundation to guide plant selection, procurement, and labeling. Agricultural extension services at Oregon State University and University of Georgia integrate the map into programming for growers and master gardener programs run in partnership with the Smithsonian Gardens. Researchers at the United States Department of Energy and National Renewable Energy Laboratory use zone data in bioenergy crop planning, while conservationists at the Nature Conservancy and World Wildlife Fund reference zones for assisted migration and restoration planning.

International and comparative systems

Comparable hardiness and climatic classification systems include maps and schemes produced by Environment Canada, the Met Office (UK) hardiness guidance, the Royal Horticultural Society hardiness ratings, and the Köppen–Geiger classifications developed by climatologists associated with University of Marburg and the Max Planck Institute for Meteorology. Botanical gardens such as Kew Gardens, the Royal Botanic Garden Edinburgh, and the Singapore Botanic Gardens use analogous frameworks, while academic comparisons have involved collaborators from ETH Zurich, Wageningen University, and CSIRO in Australia.

Category:United States Department of Agriculture Category:Climatology