Sean Barry at the Arbor Day Foundation isn't surprised to see the changes. Horticulturists started asking the foundation for new data years ago because they felt the 1990 map was no longer relevant, he said.
"In most cases it's been a shift of half a zone, which isn't really a large magnitude," he pointed out. "But a couple of places at the margins [between zones] have been really interesting."
For example, Cleveland, Ohio has shifted its zone to a warmer winter rating of 6. Noelle Akin at Cleveland's Petitti Garden Center said they're telling their customers to stick to zone-5 rated plants as they always have, but expects they'll see more Ohioans trying their hand at plants from southern states.
"Gardening is a lot of experimenting," she said. "If you're a true gardener, you'll try new things. Just be aware this isn't a drastic change."
And it's not all good news for gardeners. Fungi and other diseases are more prominent in some areas, affecting cold weather trees like Colorado blue spruces in Ohio, Akin said. A bacterial infection that chokes vining grapes has been spreading north and west in Virginia, says Wolf. And the warmer winters have caused insect populations, such as beetles which destroy crops and trees, to swell.
The growing season in Virginia has expanded an extra three to four weeks, which means more time spent fighting the pests and diseases that pop up with the buds each spring, making the longer season more of a problem than a profit, Wolf said.
The sugar collection season for maple trees has shortened by 10 percent over the last forty years, said Timothy Perkins of the University of Vermont. If these warming trends continue, cold-loving trees like the paper birch could start migrating north, said Lois Berg Stack, professor of sustainable agriculture at the University of Maine.
But Stack warns gardeners against what she calls "zone envy."
"It's very tempting to look at the map and see a warming trend and try to grow different plants...but it's not a guarantee."
From PBSNewshour (find the original story here); reprinted with permission.