The Plant Hardiness Zone is a map created by the USDA and is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 10ºF zones.

The USDA Hardiness Zone Map divides North America into 11 separate planting zones; each growing zone is 10°F warmer (or colder) in an average winter than the adjacent zone. If you see a hardiness zone in a gardening catalog or plant description, chances are it refers to this USDA map.