Hello Gardeners, I’m Amanda McNulty with Clemson Extension and Making It Grow. Plant cold hardiness zones give us the average lowest winter temperature we might expect in a particular part of the country. Statisticians use thirty years of records to get what meaningful number. The USDA plant cold hardiness zone map is based on the average annual minimum winter temperature, divided into different 10-degree Fahrenheit zones. The continental United States encompasses 9 zones, with zone three being the coldest and 10 the warmest. Now this doesn’t mean you can’t get colder weather than what your zone lists; it‘s an average and as our climate changes extremes in weather events are what we can expect. It’s important to know your zone when you are selecting plants; the tags that accompany plants will list the range of zones in which that plant should be able to survive the average lowest temperature.