Hardiness zone

A hardiness zone (a subcategory of vertical zonation) is a geographically defined area in which a specific category of plant life is capable of growing, as defined by climatic conditions, including its ability to withstand the minimum temperatures of the zone (see the scale on the right or the table below). For example, a plant that is described as "hardy to zone 10" means that the plant can withstand a minimum temperature of −1 °C (30 °F). A more resilient plant that is "hardy to zone 9" can tolerate a minimum temperature of −7 °C (19 °F). First developed by the United States Department of Agriculture (USDA), the use of the zones has been adopted by other countries.