Finding your U.S.D.A. Hardiness Zone and What Does It Mean?
The United States Department of Agriculture has developed a map dividing the country into different zones based on averages of minimum temperatures. In general, if you chose plants that are within your hardiness zone you will have more success growing them. This is only meant to be a guide.
There are many factors that influence plant hardiness. Microclimates, small-scale variations in climate, can cause changes in average temperatures. A sheltered, sunny spot next to a building will likely be warmer than average, while an exposed site at the top of a hill may be cooler. Hands on experience in your own garden will be your best guide.