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As of the most recent release, the November 2023 map has the US broken into 13 cold hardiness zones in 10-degree Fahrenheit intervals, with each zone further broken into “a” (the warmer half ...
The 2023 USDA plant hardiness zone map, which shows which areas of the country are suitable for growing plants and crops based on the lowest temperatures during the growing season.
That compares to the fewer than 8,000 stations used for the 2012 map, according to the USDA. The new 2023 map also is divided into 10-degree Fahrenheit zones and further divided into 5-degree ...
In November 2023, the USDA released another updated version of their plant hardiness map, based on 1991–2020 weather data across the United States. The updated map shows continued northward movement of hardiness zones, reflecting a continued warming trend in the United States' climate.
The USDA rejected the AHS 2003 draft map; the agency stated it would create its own map in an interactive computer format. As of August 2010 the AHS and the National Arboretum websites still present the 1990 map as current. In 2006, the US National Arbor Day Foundation completed an extensive updating of U.S. Hardiness Zones. It used essentially ...
Hardiness of plants is defined by their native extent's geographic location: longitude, latitude and elevation. These attributes are often simplified to a hardiness zone. In temperate latitudes, the term most often describes resistance to cold, or "cold-hardiness", and is generally measured by the lowest temperature a plant can withstand.
For example, Seattle, Washington, and the city of Austin, Texas, are both in the USDA hardiness zone 9a because the map is a measure of the coldest temperature a plant can handle.
Hopkins' bioclimatic law states that in North America east of the Rockies, a 130-m (400-foot) increase in elevation, a 4° change in latitude North (444.48 km), or a 10° change in longitude East (two-thirds of a time zone) will cause a biological event to occur four days later in the spring or four days earlier in the fall. [1]