The USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location.
The hardiness zone map is a geographically zoned map used to indicate the persistence of particular plant species for each individual zone. Gardeners commonly use zones as a way to classify plants, indicating their ability to carry out a natural life cycle with one season or the capability of a biennial or perennial to thrive from season to season. The zones of the plant hardiness map are defined by the lowest mean temperature over a five year period. Plant species are then assigned the classification of the lowest zone they will persist. Elements that influence hardiness zones or minimum yearly temperatures are altitude, latitude and proximity to the sea coast or a large body of water. The plant hardiness zone map is only intended as a basic guideline and does not take into consideration many factors such as mean temperature highs, humidity, snow cover, number of frost days per season.