The USDA Plant Hardiness Zone Map is the go-to resource for many gardeners — and it shows it really is getting warmer across the U.S. How much warmer? The recently updated map shows, on average, temperatures 2.5 degrees warmer than the 2012 map, Chris Daly, director of the PRISM Climate Group at Oregon State University, told NPR. The map, showing which plants are most likely to survive the…