Whenever you purchase a new perennial plant, shrub, or tree, you've probably noticed information about hardiness zones on the ...

Plant hardiness zone maps are, well, all over the map. Consider the number assigned to your zip code as a starting point. You may live right at the break between one zone and the other.

But what, exactly, does that mean? The numbers refer to the U.S. Department of Agriculture’s Plant Hardiness Zone Map, which divides the country into geographic zones that have similar average ...