According to the USDA, the plant hardiness index for
Background Information How the map was started
Every plant can adapt to a range of environments. Gardeners have learned through
experience where the great variety of landscape plants can be grown.
Over the years many schemes have been proposed to help gardeners locate
those environments when they introduce new species, forms, and cultivars.
The pooling of many of these schemes culminated in the development of the widely used
'Plant Hardiness Zone Map,' under the supervision of Henry T. Skinner, the second director
of the U.S. National Arboretum. In cooperation with the American Horticultural Society,
he worked with horticulral scientists throughout the United States to incorporate
pertinent horticultural and meteorlogical information into the map.
Indicator Plant Examples
The following are names of representative persistent plants listed under the coldest zones
in which they normally succeed. Such plants may serve as useful indicators of the cultural possibilites
of each zone.