When gardening and planting trees up here in northern Wisconsin, I pay a lot of attention to United States Department of Agriculture (USDA) hardiness zones.
My general region is rated Zone 4, which means it’s too cold for many popular trees and plants to survive the winters. When perusing plants catalogs and websites, I always check to see which zones the plants are rated to handle. If one says “Zones 5-9,” for example, I’m forced to choose a different option.
I know I’m not alone in seeking zone-appropriate plants for my region. You’ve likely done the same. The question is, what do the USDA hardiness zones actually define? And are they the be-all end-all when it comes to determining whether a given plant will grow in a particular region?
Before we dig into our soil for to start gardening, let’s dig into the USDA hardiness zones and learn more.
What are the USDA hardiness zones?
In order to help farmers and gardeners determine which plants are suitable for their region, the USDA has divided the U.S. (and Puerto Rico) into 13 zones based on temperature. The result is a color-coded map with each color representing a different zone.
The zones are further subdivided into “a” and “b” categories. So “Zone 7” technically encompasses “Zone 7a” and “Zone 7b,” with the “a” zone being slightly colder.
Takeaways from the USDA hardiness zones
Despite their shortcomings, USDA hardiness zones provide solid guidelines for choosing plants based on winter hardiness. And if you’re growing plants rated a zone or two hardier than the zone you occupy (for example, growing Zone 3 and 4 plants in Zone 5), you should be pretty much good to go.
But with a little thought and care, you might be able to stretch the rated hardiness of plants further than you might imagine.
Proper mulching, protection from windbreaks, consistent snow cover, and planting near buildings can all improve the chances of a plant surviving in a hardiness zone on the edge of what it’s rated to handle.
Have fun planting!
