A hardiness zone is a geographically defined area in which a specific category of plant life is capable of growing, as defined by climatic conditions, including its ability to withstand the minimum temperatures of the zone. For example, a plant that is described as "hardy to USDA Zone 10" means that the plant can withstand a minimum temperature of 30-35 degrees F. A more resilient plant that is "hardy to USDA Zone 4" can tolerate a minimum temperature of -25 to -30 degrees F. First developed for the United States by the Department of Agriculture (USDA), the use of the zones has been adopted by other nations.

If you live in the western U.S., you'll find that nurseries, garden centers, and other western gardeners often refer to the Sunset Climate Zones rather than the USDA plant hardiness zones.

The Gardenality website uses the USDA Hardiness Zones. For the convenience of those who live and garden outside the U.S., the minimum temperature is also provided along side the USDA Zone.

Questions About Temperature & Hardiness Zones