Sunday, July 22, 2007

Climate change redraws the map for gardeners

Washington Post: If you live in the southern part of Northern Virginia, I've got news for you: You're now in North Carolina. If you live in Maryland, you're now in Virginia. No, your state boundaries haven't been redrawn. But something else has -- a map of plant hardiness zones in the United States.

As a gardener, you know that plants grow best in their comfort zone -- not too hot or too cold. For decades, landscape professionals, gardeners, foresters, and nursery and garden-center staff have relied on the Agriculture Department's hardiness zone map to determine which plants are appropriate for a given area. The map, developed by the National Arboretum, the American Horticultural Society and plant scientists across the country, was designed to help expand the range of plant materials that could be cultivated by predicting which flora would survive in specific locations.

However, many horticultural professionals think the map is out of date. The USDA last revised it in 1990, based on data from 1974 to 1986. But the climate has changed since the mid-1980s. The agency rejected a proposed update in 2003 and plans to release a new map as soon as this year.

Enter the National Arbor Day Foundation, whose members include arborists, urban and rural foresters, and homeowners who care about trees.

"The USDA map just doesn't seem right anymore," said Woody Nelson, vice president of communications for the foundation. "So we took it upon ourselves to do our own map." For an updated take on which plants are hardy in your region, look at the foundation's map online at

…The changes were startling. Many areas jumped one or two zones higher. "The climate has changed," Nelson said. "It has warmed."

...While the new map reflects recent reality, it's not a predictor of future climate conditions, and not everyone welcomes creeping heat. The Union of Concerned Scientists recently predicted that much warmer temperatures in the Northeast would kill the ski industry, lead to longer and more severe droughts, change the coastline and wipe out some fishing. But the report noted that recent efforts to reduce greenhouse gases in the area are a step toward maintaining a stable climate.

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