New USDA Hardiness Zone Map Shows Warming Trend

In addition to being used for quick-reference by many gardeners, the map also helps set policies for crop insurance. The overall shift to warmer zones may spark some innovation in U.S. farming, says David Wolfe, a soils and crops scientist at Cornell University. “It makes a gardener or farmer a little bit more comfortable with experiments,” Wolfe says.

Many farmers haven’t waited for the new map to take chances, instead utilizing the warming trend that has continued since the 1970s. In central New York, Wolfe says, entrepreneurs began growing European wine grapes, betting correctly that the local climate would continue to be warm enough to sustain them. And soybean production has increased in northern New York from 40,000 acres to 250,000 acres in recent years, which has only been possible with the warmer temperatures, Wolfe says. When farmers need to replace old orchard trees or grape vines, they now might choose to consider varieties that do well in warmer climates.

But as warmer hardiness zones creep northward, so will new weeds and pests that previously had been confined down South. Worse, farmers won’t be able to count on natural predators to appear and keep a new pest in check, he says.

Farmers still will need to check other weather-condition yardsticks, like soil temperature and long-term weather forecasts, before planting less-hardy crops, says Lynda Prim, a fruit and vegetable technical adviser with the Northeast Organic Farming Association of Vermont. She also recommends farmers plan for surprise weather events that may come with the warm temperatures, as weather patterns have proven unstable in recent years.

A question remains whether the new weather model, although vastly more detailed, provides a complete picture of temperature patterns. There is some concern that the new map, which reaches back 30 years, overlaps with the information found in the 1990 map, and therefore may not reflect fully the reality of increasing temperatures in recent years.

While happy with the new USDA Plant Hardiness Zone Map, Daly says there is always room for improvement. He hopes the PRISM program will work to continuously improve the hardiness zone map’s accuracy.

“We hope our (2012) maps look antiquated in another 10 or 20 years,” Daly says.

Check out the new map on the USDA Plant Hardiness Zone Map page.