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USDA Hardiness Zones and Average Annual Minimum Temperature Range

Zones 2-10 in the map have been subdivided into light and dark colored sections (a and b) that represent 5° F (2.8° C) differences within the 10° F (5.6° C) zone. The light color of each zone represents the colder section; the dark color, the warmer section.
Zone 11 represents any area where the average annual minimum temperature is above 40° F (4.4° C).
The map shows twenty latitude and longitude lines. Areas above an arbitrary elevation are traditionally considered unsuitable for plant cropping and do not bear appropriate zone designations. There are also island zones that, because of elevation differences, are warmer or cooler than the surrounding areas and are given a different zone designation.
Note that many large urban areas carry a warmer zone designation than the surroundingcountryside.
The maps contain as much detail as possible, considering the vast amount of data on which it is based and its size.
Color Code for Plant Hardiness Zone Maps
  Zone     Fahrenheit       Celsius       Example Cities  
1  Below -50 F   Below -45.6 C Fairbanks, Alaska;   Resolute, Northwest Territories (Canada) 
2a -50 to -45 F   -42.8 to -45.5 C Prudhoe Bay, Alaska;   Flin Flon, Manitoba (Canada) 
2b -45 to -40 F -40.0 to -42.7 C Unalakleet, Alaska;   Pinecreek, Minnesota 
3a -40 to -35 F -37.3 to -39.9 C International Falls, Minnesota;   St. Michael, Alaska
3b -35 to -30 F -34.5 to -37.2 C Tomahawk, Wisconsin;   Sidney, Montana
4a -30 to -25 F -31.7 to -34.4 C Minneapolis/St.Paul, Minnesota;   Lewistown, Montana
4b -25 to -20 F -28.9 to -31.6 C Northwood, Iowa; Nebraska
5a -20 to -15 F -26.2 to -28.8 C Des Moines, Iowa;   Illinois
5b -15 to -10 F -23.4 to -26.1 C Columbia, Missouri;   Mansfield, Pennsylvania
6a -10 to -5 F -20.6 to -23.3 C St. Louis, Missouri; Lebanon, Pennsylvania
6b -5 to 0 F   -17.8 to -20.5 C McMinnville, Tennessee;   Branson, Missouri 
7a 0 to 5 F -15.0 to -17.7 C Oklahoma City, Oklahoma;   South Boston, Virginia
7b 5 to 10 F -12.3 to -14.9 C Little Rock, Arkansas;   Griffin, Georgia
8a  10 to 15 F -9.5 to -12.2 C Tifton, Georgia;   Dallas, Texas 
8b 15 to 20 F -6.7 to -9.4 C Austin, Texas;   Gainesville, Florida
9a 20 to 25 F -3.9 to -6.6 C Houston, Texas;   St. Augustine, Florida
9b 25 to 30 F -1.2 to -3.8 C Brownsville, Texas;   Fort Pierce, Florida
10a 30 to 35 F 1.6 to-1.1 C Naples, Florida;   Victorville, California
10b 35 to 40 F 4.4 to 1.7 C Miami, Florida;   Coral Gables, Florida
11 above 40 F above 4.5 C Honolulu, Hawaii;   Mazatlan, Mexico
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