Have you ever seen a new or peculiar plant, and wondered if it would grow in your area? The most important factor limiting plant growth across large geographic regions (other than water availability) is a plant’s “hardiness” or ability to tolerate a range of temperatures. Luckily, the United States Department of Agriculture created an interactive tool that maps the average annual minimum temperature in any area, allowing professionals and hobbyist gardeners to describe plants with this system. Regions are split into zones based on their average annual low temperature. Each zone has a range of 10 degrees, and then is subdivided by 5 degree increments denoted by an “a” or “b.” The range of zones stretches from 1a to 13b. With zone 1a having an average low between -60˚ and -55˚F, and zone 13b with an average low between 65˚ and 70˚F.
Horticulturists use this tool to assign plants to a specific zone or range of zones, within which they are “hardy,” allowing an interested individual to determine where plants will thrive. You can check for this information when purchasing plants, as it is added to the tag of almost all commercial plants sold in-store and online.
Most of the state of Kentucky is located in Zone 6b, (average annual minimum between -5˚ and 0˚F) which includes us here at Bernheim. Southwestern Kentucky has zone 7a present while Northeastern parts of the state are in zone 6a. There are many trees and shrubs available to zone 6 growers that might surprise you, such as the Hardy Banana (Musa basjoo) or Trifoliate orange (Poncirus trifoliatum). To check what zone you’re located in, check out the USDA tool.
Matthew London, 2016 Horticulture Intern, Senior at Western Kentucky University