New Plant Hardiness Zone Map Reflects Warming Trends
Thursday, Jan. 26, 2012, 3:45 p.m. EST
The U.S. Department of Agriculture released a new version of its Plant Hardiness Zone Map, the first update of the map since 1990.
Jointly developed by the USDA’s Agricultural Research Service and Oregon State University, the new Plant Hardiness Zone Map adds two new warm zones: zone 12 (50-60 degrees Fahrenheit) and zone 13 (60-70 degrees Fahrenheit). The 1990 Plant Hardiness Zone Map had 11 zones, with zone 11 being anything warmer than 40 degrees Fahrenheit.
In addition, zone boundaries shifted in many areas, with the new Plant Hardiness Zone Map generally 5 degrees warmer than the previous map for much of the country, the USDA reported, although some areas changed to cooler zones.
The changes came because the Plant Hardiness Zone Map used a longer and more recent data collection period and the mapmakers used more sophisticated methods for mapping zones, such as algorithms that considered changes in elevation, nearness to large bodies of water and relative position on the terrain (such as valley bottoms versus ridge tops), the USDA reported. The Plant Hardiness Zone Map also uses data from more weather stations, presumable increasing its accuracy.
The zone designations represent the average annual extreme minimum temperatures at a given location during a particular time period as low temperature during the winter is a crucial factor in plant survival, according to the USDA.
The new Plant Hardiness Zone Map reflects data collected over the 30-year period 1976-2005; the 1990 version was based on a 13-year period from 1974-1986.
“This is the most sophisticated Plant Hardiness Zone Map yet for the United States,” said Catherine Woteki, USDA under secretary for research, education and economics. “The increases in accuracy and detail that this map represents will be extremely useful for gardeners and researchers.”
The new Plant Hardiness Zone Map was designed for the Internet and uses an interactive format based on a geographic information system. The Plant Hardiness Zone Map website allows users to find their zone by zip code feature and can be downloaded for free.
The USDA will not print a poster-sized version of the Plant Hardiness Zone Map for purchase as it had with previous versions.
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New Plant Hardiness Zone Map Reflects Warming Trends
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