A blogger I follow, Skippy's Vegetable Garden, posted today that her planting zone had changed. The USDA just upgraded its plant zone hardiness map, shifting its zones slightly northward. The map measures average annual extreme minimum temperature. Her zone changed from 6a (avg -10 degrees) to 6b (avg -5 degrees). We knew it was coming, but it's eery to see global warming in action. Check out your new zone here.