USDA Hardiness Zones
The USDA Plant Hardiness Zone map is the standard for gardeners to determine what plants will grow in specific areas. The map divides the United States into 11 distinct zones based on regional temperature. Each zone border is 10°F warmer (or colder) during an average winter than the adjoining zone.
USDA Plant Hardiness Zone Map, 2012. Agricultural Research Service, U.S. Department of Agriculture. Accessed from https://planthardiness.ars.usda.gov.