Hardiness Zones, Gardening Zones, Growing Zones and Plant Zones refer to defined geographic regions that can support specific plants, flowers and trees. The zones define a minimum range of temperatures that a plant or tree can survive safely in that zone. The most commonly used Hardiness Zones were defined by the USDA. The USDA provides a hard copy map that displays these zone throughout the US. The last update to this map covers minimum temperatures from 1961 to 1990. An updated map is currently in production, but has not been released yet. Plant Maps provides the only interactive version of the USDA hardiness zone map available on the internet.