Federal agriculture officials have updated a valuable tool for gardeners and researchers for the first time since 2012.
The Plant Hardiness Zone Map (PHZM) provided by the U.S. Department of Agriculture (USDA) is an important tool for the approximately 80 million American gardeners and growers – its most frequent users.
The map helps them determine the best plants to grow in their specific location by considering the low winter temperatures, which are a vital factor for the survival of plants.
The agency, along with Oregon State University’s PRISM Climate Group, jointly developed the most accurate and detailed map ever released by the USDA’s Agricultural Research Service. It incorporates data from 13,412 weather stations compared to the 7,983 used for the 2012 map.
"The addition of many new stations and more sophisticated mapping techniques using the latest PRISM technology led to a more accurate and detailed Plant Hardiness Zone Map but also produced localized changes that are not climate-related," said Christopher Daly, director of the PRISM Climate Group and the map’s lead author.
The map is based on 30-year averages (1991-2020) for the lowest annual winter temperatures within specified locations. The 2012 edition was based on averages from 1976-2005.
"Overall, the 2023 map is about 2.5 degrees warmer than the 2012 map across the conterminous United States," Daly said. "This translated into about half of the country shifting to a warmer 5-degree half zone, and half remaining in the same half zone. The central Plains and Midwest generally warmed the most, with the southwestern U.S. warming very little."
Although a paper version of the new map will not be available for purchase from the government, anyone may download the new map free of charge and print copies as needed.
Original article source: New hardiness zone map released by USDA to help 80 million US gardeners prepare for winter