The U.S. Department of Agriculture (USDA) updated its Plant Hardiness Zone Map. USDA’s Plant Hardiness Zone Map is the standard by which growers can determine which plants are most likely to thrive at a location. The USDA said this 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.
In addition to the map updates, the USDA expanded the Plant Hardiness Zone Map website to include a “Tips for Growers” section, which provides information about USDA ARS research programs of interest to those who grow and breed plants.
The 2023 map is based on 30-year averages of the lowest annual winter temperatures at specific locations. Like the 2012 map, the 2023 web version offers a geographic information system (GIS)-based interactive user-friendly format. 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 used for the 2012 map.
Plant hardiness zone designations represent the “average annual extreme minimum temperature” at a given location during a particular time period (in this instance, 30 years). The USDA said these 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 features 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.
The Plant Hardiness Map is available online at https://planthardiness.ars.usda.gov/.