“Among the most important factors determining which plants can survive where is how cold the winter is. If you’re planting a garden this spring, this set of maps can help you see how planting zones across the country have shifted ever so subtly over the past few decades in response to warming climate. Click titles below maps to switch map view. The maps at right show average minimum winter temperatures across the contiguous United States divided into 10-degree planting zones for the most recent U.S. Climate Normals (1981-2010), the old Normals (1971-2000), and how the margins of the planting zones shifted between the two time periods as a result of warmer winter minimum temperatures. In these areas, warmer nights are allowing plant species to shift their range northward. Updated each decade, the U.S. Climate Normals from NOAA’s National Climatic Data Center are 30-year averages of many pieces of weather information collected from thousands of weather stations nationwide. Each time they are updated, an old decade is dropped, and a new one is added. The last update was in July 2011: the decade 1971-1980 was dropped, 2001-2010 was added, and the new 30-year window for the U.S. Climate Normals became 1981-2010.”