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California Institute of Technology Landscape Master Plan
USDA Unveils New Plant Hardiness Zone Map

USDA Unveils New Plant Hardiness Zone Map

The U.S. Department of Agriculture has released a new version of its Plant Hardiness Zone Map, the first time since 1990. The map developers, USDA's Agricultural Research Service and Oregon State University's PRISM Climate Group, say it has greater accuracy and detail.

 

The map offers a Geographic Information System-based interactive format, specifically designed to be internet-friendly. The map website includes a "find your zone by ZIP code" function.

There are 13 zones, an addition for the first time of zones 12 (50-60 degrees F) and 13 (60-70 degrees F). Each zone is a 10-degree Fahrenheit band, further divided into A and B 5-degree Fahrenheit zones. The map uses data measured at weather stations from 1976 to 2005. The old map was based on temperature data for only the 1974-1986 period.

More sophisticated methods for mapping zones between weather stations include algorithms that considered changes in elevation, nearness to large bodies of water, and position on the terrain, such as valley bottoms and ridge tops.

The new Plant Hardiness Zone Map is available at http://www.planthardiness.ars.usda.gov/.

 
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