The United States Department of Agriculture (USDA) created this map to give gardeners a helpful tool for selecting and cultivating plants. The map divides North America into 11 zones based on each area’s average minimum winter temperature. Zone 1 is the coldest and Zone 11 the warmest. Recently, the zones were further divided into “a” and “b”, with “a” being the colder portion. To locate your zone, refer to the map here, or for the most up-to-date information, visit the National Arbor Day Foundation’s Web site: www.arborday.org/media/zones.cfm.