BY USING THIS WEBSITE OR THE CONTENT THEREIN, YOU AGREE TO THE TERMS OF USE. Growers can determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 10-degree F zones.Plant Hardiness Zones derived the USDA. Data generalized by Oakland County IT/GIS for viewing at larger scales.
From the USDA:
USDA Plant Hardiness Zone Map
The 2012 USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 10-degree F zones.More information can be found here: http://planthardiness.ars.usda.gov/PHZMWeb/About.aspx