North America has a wide variety of climates from tropical Florida to icy Alaska and there are no plants that will happily survive everywhere. In particular, some plants will endure the coldest of winters, while some will be killed by the lightest frost. But how do we know which plants will survive where? And how we know which plants will survive the winter temperatures in our yard?
To help gardeners and farmers understand all this, the USDA has collated records of the average coldest winter temperatures from thousands of weather stations all over the country. This data has all been plotted on a map and the country divided into thirteen zones which are displayed on the USDA Hardiness Zone map and numbered zone 1 (the coldest) to zone 11 (the warmest). There are two more warmer zones (Z12 and Z13), but these cover tiny tropical areas.
