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New Plant Hardiness Zone map released

An updated USDA Hardiness Zone Map was released

An updated USDA Hardiness Zone Map was released Jan. 26, 2012. Credit: U.S.D.A.

The U.S. Department of Agriculture unveiled its long-awaited update of its 1990 U.S. Plant Hardiness Zone Map Thursday at the National Arboretum in Washington. The map, which was revised to reflect changing climate patterns across the country, is vital to gardeners trying to determine which plants are most likely to thrive in a location. The new version reveals that some plants and trees can survive farther north than they could in the past.

In 2006, the Arbor Day Foundation issued its own revision of the old map, indicating  that zones were creeping northward, meaning that northern areas were falling into zones that previously had encompassed warmer, southern areas. In some cases, this meant plants that hadn't been able to survive winters in a region were becoming suitable for planting there.

 The new USDA map is based on the average annual minimum winter temperature and is divided into 10-degree Fahrenheit zones. In the works for several years, it replaces a 22-year-old version that was not easily accessible to the public. Gardeners were likely to have seen it only as it was printed in seed catalogs, and those versions often were too small to allow for pinpointing of an exact location. The only online version of the map could not be resized by users and was not searchable, so determining a  zone -- which can vary from town to town -- often was difficult. A new interactive functionality makes it a snap to find zones on the 2012 map simply by typing in a ZIP code. 

On the old map, most of Long Island fell into Zone 7, except for a strip in the center of Suffolk County around the Pine Barrens, which was in Zone 6. The update puts the majority of Long Island in Zone 7a, but the northern section of western and central Nassau, and the southern part of the Island from the Queens-Nassau border all the way east to the Gilgo Beach area is now part of 7b, which is warmer. A few small, scattered spots around Manorville, North Hampton and Baiting Hollow also now fall into 7b, with the rest of Suffolk, including the formerly 6a Pine Barrens region, in 7a.

Experts believe there will be more changes to come. “The northward march of the hardiness zones illustrates the continued warming that has occurred across the United States and around the globe in recent decades, particularly in winter," according to Art DeGaetano, climatologist, professor and director of the Cornell-based NOAA Northeast Regional Climate Center. "Projections for state-of-the-art climate models indicate that winter temperatures will continue to warm through the 21st century."

Additional updates and changes to the hardiness map will be necessary in years to come, DeGaetano said, adding that "by 2080, the hardiness zones that currently cover the area from southern Virginia to Northern Georgia may replace those that we see across New York in the current update.”

 William Miller, one of the world’s leading experts on floriculture and the physiology of ornamental plants, notes that “experienced gardeners are always pushing the envelope by trying new plants, and especially those that ‘aren't hardy’ in their area. Really crusty gardeners sometimes say that they need to kill a plant three times to be certain it won't grow in their area.

“Aside from global warming or simply more and better data leading to a more accurate map, there is always microclimate variation in any locale, and a few feet alteration in planting site, better drainage, locating a plant around a corner, presence of snow cover, mulch, or protection from wind can make a huge difference in winter hardiness," Miller said.

“Especially with herbaceous perennials, that are relatively inexpensive and in any case almost always a lesser investment than trees or shrubs, one should experiment and try to push the hardiness rating. You never know what might survive.”

Where are you now? Find your new zone here

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