No need to re-invent the wheel here, Gary. There are two sources I can think of that you should look at for this purpose:
The US Dept. of Agriculture has their plant hardiness zone maps. They aren't all that useful for gardeners as they were intended for farmers to use. But growers of nursery plants for home gardeners use their hardiness zones as a beginner reference.
http://www.planthardiness.ars....
Sunset Magazine came up with a much better, more informative map for gardeners:
http://www.sunset.com/garden/c...
