Hardiness Zones

Assuming a gardener provides the right amount of light, water and nutrients, the one remaining intangible in ensuring plant growth is temperature, especially cold temperatures. The United States Department of Agriculture (USDA) has developed a standardized Hardiness Zone Map to assist gardeners in identifying the average annual minimum temperature for their location and plants that are adapted to their particular Hardiness Zone.

The following pages describe the methodology used to develop Hardiness Zone Maps, recent proposals to change the USDA Hardiness Zone Map and alternative approaches to determining the optimum growing climate for a plant. There are few authoritative references on the Internet that provide a complete discussion of Hardiness Zone Maps, so the following is an attempt to consolidate the sources. Since I've likely made some mistakes or over looked some important data, I'd appreciate any suggestions for changes.

1. What is a Hardiness Zone?
2. The 1990 USDA Hardiness Zone Map and Its Predecessors
3. Proposed Changes to the 1990 USDA Map -
• American Horticultural Society (AHS) draft changes
• Other Approaches
4. Evolution of hardiness zone maps for Florida
5. What does the future, especially the threat of global warming, hold in store?