As winter retreats northward across the nation, gardeners are cleaning tools and turning attention to spring planting. But climate change is adding a new wrinkle, and now a standard reference – the U.S. Department of Agriculture's Plant Hardiness Zone Map – is about to make very clear how much rising temperatures have shifted planting zones northward.
The guide, last updated in 1990, shows where various species can be expected to thrive. A revision is expected sometime this year, and while the agency hasn't released details, horticulturalists and experts who have helped with the revision expect the new map to extend plants' northern ranges and paint a sharp picture of the continent's gradual warming over the past few decades. The new version will have a wide audience: the National Gardening Association estimates 82 million U.S. households do some form of gardening, a number expected to increase as more Americans plant vegetable gardens to cut food costs.
Read the rest of the article; it's quite interesting about the problems with the current map, and what they plan to include in the new map.