Most plants are adaptable to one degree or another and with a little manipulation in planting locations, many plants will do quite well in areas they normally would not grow. But, whether you plant varieties hardy in your area, manipulated the growing area or plant in movable containers, you still need to know the areas in which a plant grows well naturally. Through many years of research and observation, the prevailing weather patterns have been noted and plotted with average low temperatures. The map and corresponding key below shows the results of such observations and translates it into growing zones that can be further translated into areas where a particular plant will grow reliably or where the same plant can be expected to require special care or fail altogether. By knowing where you wish to grow a particular plant and correlating it to the map below, you can get a good estimation of the success you will have with that plant from a winter cold standpoint. It makes good gardening and landscaping sense to start with the "Plant Hardiness Zone Map" before making any decisions on plant choices for your area. 
Hardiness Zones -- Details  | 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 20 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 surrounding countryside. The map-contains as much detail as possible, considering the vast amount of data on which it is based and its size. |
USDA Hardiness Zones and Average Annual Minimum Temperature Range
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| 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 |
the "Hillbilly Gardener" |
