Growing Zones

 

What Is a Hardiness Zone?

Using historical temperature data, the USDA has divided the country into 13 hardiness zones, ranging from 1 (coldest) to 13 (warmest). Each of these zones is further divided into “A” and “B” for greater accuracy, with A being colder than B. These zones are defined by average annual minimum temperature. For example, a zip code in which the average annual minimum temperature is between -15 and -10 Fahrenheit is assigned to hardiness zone 5B.

The idea behind the zones is that gardeners can look up their hardiness zone and use it to identify plants which will thrive in their area. For example, a gardener in Northwest Connecticut (hardiness zone 5) will confidently plant a variety that has been rated hardy to zone 4, but would generally not plant a variety that is only rated hardy to zone 6, because the zone 6 plant would not likely survive their typical winter.

 

 

Zone Fahrenheit Celsius Example Cities
1a -60 to -55 F -48.3 to -51.1 C Fairbanks, Alaska; Resolute, Northwest Territories (Canada)
1b -55 to -50 F -45.6 to -48.3 C North Slope, Alaska
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 San Diego, California; Coral Gables, Florida
11a 40 to 45 F 4.4 to 7.2 C Miami, Florida; Mazatlan, Mexico
11b 45 to 50 F 7.2 to 10 C Marathon, Florida; Florida Keys
12a 50 to 55 F 10 to 12.8 C Portuguese Azores; Spanish Canary Islands
12b 55 to 60 F 12.8 to 15.6 C San Juan, Puerto Rico; Honolulu, Hawaii
13a 60 to 65 F 15.6 to 18.3 C Los Angeles, Califorina; Kaneohe, Hawaii
13b 65 to 70 F 18.3 to 21.1 C Carolina, Puerto Rico; Puerto Rico