I have been recently hearing of “heat zones” in addtion to “hardiness zones” What is the difference?
The hardiness zones were established by the USDA to rate plants according to their cold hardiness. New “heat zones” have been developed by the American Horticulture Society to rate plants according to how much heat they can stand. There are 12 zones based on the average number of days the area experience temperatures above 86 degrees F. Not all plants have been classified yet, but if you do see a heat zone rating, Northeast Tennessee is rated a 5 in the mountains and a 6 elsewhere. That means that in heat zone 5 there are 31 to 45 days a year above 86 degrees and zone 6 has 46 to 60 days a year above 86 degrees F. By comparing the two charts, you can get a good idea of how particular plants will perform for you.
