1990 version shows in detail the lowest temperatures that can be expected each year in the United States, Canada, and Mexico.
These temperatures are referred to as "average annual minimum temperatures" and are based on the lowest temperatures recorded
for each of the years 1974 to 1986 in the United States and Canada and 1971 to 1984 in Mexico. The map shows 10 different
zones, each of which represents an area of winter hardiness for the plants of agriculture and our natural landscape.
It also introduces zone 11 to represent areas that have average annual minimum temperatures above 40 F (4.4 C) and that are
therefore essentially frost free.
How to Use the New Map 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.
Below -50 F
Resolute, NT (Canada)
-50 to -45 F
Prudhoe Bay, Alaska; Flin Flon, Manitoba
-45 to -40 F
Unalakleet, Alaska; Pinecreek, Minnesota
-40 to -35 F
International Falls, MN; St. Michael, Alaska
-35 to -30 F
Wisconsin; Sidney, Montana
-30 to -25 F
Minneapolis, MN; Lewistown, Montana
-25 to -20 F
Northwood, Iowa; Nebraska
-20 to -15 F
Des Moines, Iowa; Illinois
Columbia, Missouri; Mansfield, PA
St. Louis, Missouri; Lebanon, PA
-5 to 0 F
McMinnville, Tennessee; Branson, MS
0 to 5 F
Oklahoma City, OK; South Boston, VA
5 to 10 F
Little Rock, Arkansas; Griffin, Georgia
10 to 15 F
Tifton, Georgia; Dallas, Texas
15 to 20 F
Austin, Texas; Gainesville, Florida
20 to 25 F
Houston, Texas; St. Augustine, Florida
25 to 30 F
Brownsville, Texas; Fort Pierce, Florida
30 to 35 F
Naples, Florida; Victorville, California
35 to 40 F
Miami, Florida; Coral Gables, Florida
above 40 F
Honolulu, Hawaii; Key West, Florida
In using the
map to select a suitable environment for a landscape plant, today's gardeners should keep in mind the following:
New Plant Management Systems.
New techniques of planting, transplanting, watering, fertilizing, and providing pest control measures
have done much to increase the vigor of landscape plants.
We have pushed the use of plants into totally artificial environments such as expressways, malls,
elevated decks, and buildings where plant roots are totally removed from the ground and its warming influence.