Plant Hardiness Zone Map
The 2012 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, click here for the interactive map . The map is based on the average annual minimum winter temperature, divided into 10-degree F zones.
The USDA system was originally developed to aid gardeners and landscapers in the United States.
The map is available as an interactive GIS-based map, for which a for broadband Internet connection is recommended, and as static images for those with slower Internet access. Users may also simply type in a ZIP Code and find the hardiness zone for that area.
If you want an accurate map to not only provide general band guidelines for the USA but can also be so detailed that your town, down to the zip code, is reported on. The hardiness scales do not take into account the reliability of snow cover. Snow acts as an insulator against extreme cold, protecting the root system of hibernating plants.
The zones do not incorporate any information about summer temperature, thus sites which may have the same mean winter minima, but markedly different summer temperatures, will be accorded the same hardiness zone.
As the USDA system is based entirely on average annual extreme minimum temperature in an area, it is limited in its ability to describe the climatic conditions a gardener may have to account for in a particular area: there are many other factors that determine whether or not a given plant can survive in a given zone.