USDA Hardiness Zones and Average Annual Minimum Temperature Range
In addition to the USDA Zone Map below, you may find a climate zone map published by Sunset Magazine helpful. It contains detailed climate information on dozens of well-defined regions throughout the continental U.S. To view the map, click here.

Why does Seeds of Change only list zone information for perennials and not annuals?

Basic Zone Chart Annual seed can generally be planted in any garden in any area of the world. The maturity of the plant will depend on the length of the growing season in specific areas. If you know how long your growing season is you can choose plants that have enough time to mature by looking at "Days to Maturity" listed on each seedpack and in each seed description, for example (60-90 days).

Successful perennial gardening requires an understanding of the hardiness zone in your specific microclimate. An easy way to find your zone is by knowing what your minimum temperature is during the wintertime. Once you know your zone you'll know if your perennial plant will be able to over-winter in your garden without dying.

The USDA provides a Hardiness Zone Map, as well as a chart to find the Average Minimum Temperature in your area. Please remember that this is a general zone chart and does not necessarily take into account the specific microclimate where you have your garden. Coldframes, south-facing slopes, heavy winter mulches, etc. can allow plants to survive in a colder zone than is indicated.
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
If you would like more information about the USDA Hardiness Zones and Average Annual Minimum Temperature Range please go to their website at The United States National Arboretum. On their site you will be able to see more detail on specific regions by state.