Growing Zones

Growing-zones help you select plants that are adapted to your seasonal climate. Plants are rated within a growing-range. For example, an azalea could be rated viable in "Zones 5-9". In this example "5" is the coldest zone where it can survive without winter protection, but it could receive occasional damage; "9" is the warmest zone where a typical winter will set the blooms. If the winter isn't cold enough and long enough, it won't bloom like it should.

The USDA developed hardiness-zones based on winter-temperatures over a 10 year period. There are micro-climates within the colder growing-zones where plants are more viable such as on a hill-top where colder air settles to a lower-elevation or in a large urban area where urban activity warms the air.

For example, Charlotte, NC is straddled between zone 7a and 7b which means the minimum winter-temperature should go to 5 degrees F in a typical year. In reality Charlotte only experiences single digits about half of the winter periods because urban-activity warms the air as much as 5 degrees compared to rural areas. Hence 5 degrees F is colder than a typical winter-minimum for Charlotte, and 8 to 10 F is more typical. The all-time record-low in Charlotte was -5 degrees F set in the early 1980s, breaking the previous record of 0 degrees F.

The table below has growing-zone maps for the lower48 states: