Planting zones show the areas in which specific plants are known to grow well, explains the National Gardening Association. These zones typically are depicted on maps used by gardeners to see where plants can adapt. The most common planting zones are based on coldest temperatures, heat days and climate.
The USDA Plant Hardiness Zone Map, considered the standard by which gardeners can determine a plant's likelihood of thriving in a particular region of the United States, is divided into 10-degree zones, according to the United States Department of Agriculture. Zones are determined by the average annual minimum winter temperature.
The AHS Plant Heat Zone Map is based on the average number of days each year that an area experiences temperatures over 86 degrees, which are known as heat days, explains the American Horticultural Society. The heat zone map is divided into 12 zones; Zone 1 averages less than one heat day a year, and Zone 12 averages more than 210 heat days.
The Western magazine Sunset states that its climate zone maps consider more than just temperature. These maps, which divide the United States into many sub-regions, account for the total climate, which includes the temperatures as well as the length of the growing season, rainfall patterns, wind and humidity. Additionally, Sunset's climate zone maps make adjustments for geographical variations in latitude, elevation, ocean influence, continental air influence and topography.