INDUSTRY NEWS
USDA unveils updated Plant Hardiness Zone Map
The U . S . Department of Agriculture ( USDA ) released a new version of its Plant Hardiness Zone Map ( PHZM ), updating this valuable tool for gardeners and researchers for the first time since 2012 . USDA ’ s 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 new map — jointly developed by USDA ’ s Agricultural Research Service ( ARS ) and Oregon State University ’ s ( OSU ) PRISM Climate Group — is more accurate and contains greater detail than prior versions .
It is available online at https :// planthardiness . ars . usda . gov /. In addition to the map updates , the Plant Hardiness Zone Map website was expanded in 2023 to include a “ Tips for Growers ” section , which provides information about USDA ARS research programs of interest to gardeners and others who grow and breed plants .
The 2023 map is based on 30-year averages of the lowest annual winter temperatures at specific locations , is divided into 10-degree Fahrenheit zones and further divided into 5-degree Fahrenheit halfzones . Like the 2012 map , the 2023 web version offers a Geographic Information System ( GIS ) -based interactive format and is specifically designed to be user-friendly . Notably , the 2023 map delivers to users several new , significant features and advances . The 2023 map incorporates data from 13,412 weather stations compared to the 7,983 that were used for the 2012 map .
Furthermore , the new map ’ s rendering for Alaska is now at a much more detailed resolution ( down from a 6-¼ -square-mile area of detail to a ¼ square mile ).
“ These updates reflect our ongoing commitment to ensuring the Plant Hardiness Zone Map remains a premier source of information that gardeners , growers and researchers alike can use , whether they ’ re located in the continental United States , Alaska , Hawaii or Puerto Rico ,” said ARS Administrator Dr . Simon Liu .
Approximately 80 million American gardeners and growers represent the most frequent users of the USDA Plant Hardiness Zone Map . However , they ’ re not the only ones with a need for this hardiness information . For example , the USDA Risk Management Agency refers
to the map ’ s plant hardiness zone designations to set certain crop insurance standards . Additionally , scientists incorporate the plant hardiness zones as a data layer in many research models , such as those modeling the spread of exotic weeds and insects .
Plant hardiness zone designations represent what ’ s known as the “ average annual extreme minimum temperature ” at a given location during a particular time period ( 30 years , in this instance ). Put another way , the designations 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 .
As with the 2012 map , the new version has 13 zones across the United States and its territories . Each zone is broken into half zones , designated as “ A ” and “ B .” For example , zone 7 is divided into 7a and 7b half zones . When compared to the 2012 map , the 2023 version reveals that about half of the country shifted to the next warmer half zone , and the other half of the country remained in the same half zone . That shift to the next warmer half zone means those areas warmed somewhere in the range of 0-5 degrees Fahrenheit ; however , some locations experienced warming in the range of 0-5 degrees Fahrenheit without moving to another half zone .
These national differences in zonal boundaries are mostly a result of incorporating temperature data from a more recent period . The 2023 map includes data measured at weather stations from 1991 to 2020 . Notably , the 2023 map for Alaska is “ warmer ” than the 2012 version . That ’ s mainly because the new map uses more data representing the state ’ s mountain regions where , during winter , warm air overlies cold air that settles into low-elevation valleys , creating warmer temperatures .
The annual extreme minimum temperature represents the coldest night of the year , which can be highly variable from year to year , depending on local weather patterns . Some changes in zonal boundaries are also the result of using increasingly sophisticated mapping methods and the
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