Your plants may have known it long before gardening maps declared it: the weather is a little toastier than it used to be. In recognition of warming temperatures, the U.S. Department of Agriculture revised its Plant Hardiness Zone Map in 2012. There are now 13 gardening zones, and each zone has inched northward. For many gardeners, this means about a half-zone change. If you were used to being in USDA Zone 6b, with an average wintertime low of -5 degrees to 0 F, you're probably now solidly in Zone 7a, which typically registers a low of 0 to 5 degrees.

A half-zone change can make a big difference in your garden. You may be able to grow plants that used to be too tender for your region; on the other hand, a plant that requires a certain amount of cold in the winter may not make it in your yard. Check plant tags before you buy; the zone information is spelled out as a range — for example, USDA Zones 5 to 8.

You can determine your gardening zone at the U.S. Dept. of Agriculture website. You can either enter your ZIP code or, for even more precision, use the interactive map to click down to within a half-mile of your home.