The temperatures shown on the garden zones map 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 planting zones, each of which represents an area of winter hardiness for the plants of agriculture and the 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.

Find the USDA Hardiness Zone you are in by using THIS MAP:

 

Garden 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) planting zones. 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 planting zone designations. There are also island planting zones that, because of elevation differences, are warmer or cooler than the surrounding areas and are given a different planting zone designation. Note that many large urban areas carry a warmer planting 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.

In using the Planting/Garden Zone map to select a suitable environment for a landscape plant, today’s gardeners should keep in mind the following:

• Stress Factors. Acid rain, gaseous and particulate pollution, security lighting, and toxic wastes, among many other stress factors, have significantly increased the potential for unsatisfactory performance of landscape plants. We need to document the tolerances of plants to these factors.
• 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. But used unwisely, these same measures can reduce plant hardiness.
• Artificial Environments. The use of plants has been pushed 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. The assortment of plants that can adapt to such environments is proving to be very restricted. Hardiness ratings alone are inadequate to guide landscapers in selecting the most successful plants.

The USDA Hardiness Zone Map divides North America into 11 separate zones; each zone is 10°F warmer (or colder) in an average winter than the adjacent zone. If you see a hardiness zone in a catalog or plant description, chances are it refers to the USDA map. To find your USDA Hardiness Zone, enter your zip code or use the map below. Click here for more information about hardiness maps.