Daily Green: You can grow Southern magnolia in Pennsylvania and kiwis in Oklahoma, but you wouldn’t know that from the USDA’s old hardiness zone map that gardeners use to plan their plantings, as USA Today details. They haven’t been updated since 1990, and the past two decades have been marked by increasingly obvious climate changes. In 2006, the Arbor Day Foundation took it upon itself to update those hardiness zone maps, and the results were shocking in their breadth, even if many gardeners had …