This week the USDA Agricultural Research Service released its new Plant Hardiness Zone Map. Strangely, I discovered this, not through the agriculture and gardening sites I follow, but through Mother Jones magazine's Blue Marble Blog. Julia Whitty points out:
The new map is interactive, which is cool, and based on a much finer data scale than the old one, which is great. And guess what. It shows that things are getting warmer. The USDA managed to pretty much bury that fact in Bureaucratese in their press release...Compared to the 1990 version, zone boundaries in this edition of the map have shifted in many areas. The new map is generally one 5-degree Fahrenheit half-zone warmer than the previous map throughout much of the United States. This is mostly a result of using temperature data from a longer and more recent time period; the new map uses data measured at weather stations during the 30-year period 1976-2005. In contrast, the 1990 map was based on temperature data from only a 13-year period of 1974-1986.
The interactive USDA Plant Hardiness Zone Map lets you select a state and "zoom in" to see surprisingly fine-grained detail. I've already zoomed in on every place I've ever tried to garden.