This is the most recently updated USDA Zone Map, showing the average annual minimum temperatures in the United States. The data on which the map is based was gathered over a period of 60 years. The map is divided into 10 different zones*, each of which represents an area of winter hardiness for plants, in 10°F increments. It also now includes Zone 11, which represents areas with average annual minimum temps above 40°F (4.4°C) and are essentially frost free. The lighter color of each zone represents the COLDER section; the darker color, the WARMER section. Zones 2-10 have been subdivided into light- and dark-colored sections (a & b) that represent 5°F (2.8°C) differences within each 10°F (5.6°C) zone. *Almost all zones have been upped one zone in warmth. Please click on map and color chart for larger images. ©2010 Mini Forests by SKY. All Rights Reserved.