A few years ago the USDA changed the hardiness zone map. Many of us in the horticultural industry were skeptical, yet warmer weather plants began showing up in nurseries. This winter, we have blown that revised map out of the water. Isolated rural areas of Ohio, Indiana AND Kentucky got into zone 3b and 4a territory this winter (Wisconsin), and we can expect to see plant damage as a result. Zone 5a and 5b temperatures were widespread this winter in Ohio, Kentucky, and Indiana (Chicago and northern Indiana on the new map).
USDA 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. The map is based on the average annual minimum winter temperature, divided into 10-degree F zones.
For the first time, the map is available as an interactive GIS-based map, for which a 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.
No posters of the USDA Plant Hardiness Zone Map have been printed. But state, regional, and national images of the map can be downloaded and printed in a variety of sizes and resolutions.