A plant “hardiness zone” is the average lowest temperature range for an area. The map has 13 of these areas called zones. Each zone has a defined temperature span of 10 degrees Fahrenheit. The zones are broken down even further, into 5 degree Fahrenheit ranges with letters “a” and “b.”
To use the zones, let’s create an example. If your zip code is 20001, (Washington D.C.) your plant hardiness zone is 7a. This means you can grow plants that do well in zone 7 and warmer (zones 7-13). Roses thrive in plant hardiness zones 5-8. This means you can grow them. If, however, you want to grow ‘Meyer’ lemons, you are out of luck. They do best in zones 8 and warmer.
If you move to an area and aren’t sure what to grow, the plant hardiness zones can help. Horticulture books will list the plants that do best in your zone. You can also visit a local nursery or garden center and ask a certified nurseryperson. If you are lucky enough to have a Cooperative Extension Office in your area, ask their Master Gardeners for information.