That's why the USDA has released an updated plant zone map informing the public what plants can be grown in what areas of the country. Unfortunately the latest map, the first update since 1990, is already obsolete.
The new USDA Plant Hardiness Zone Map, which predicts which trees and perennials can survive the winter in a given region, was a long time coming. Temperature boundaries shown in the latest version have shifted northward since the last one appeared in 1990. But the true zones have moved even further, according to [City University of New York] Professor [Nir] Krakauer’s calculations.
“Over one-third of the country has already shifted half-zones compared to the current release, and over one-fifth has shifted full zones,” Professor Krakauer wrote this summer in the journal “Advances in Meteorology.”
This means that fig trees, once challenged by frosty temperatures above North Carolina, are already weathering New York City winters thanks to changing temperatures and the insulating effect of the metropolis. Camellias, once happiest south of Ohio, may now be able to shrug off Detroit winters.
...“What is happening is that the winter is warming faster than the summer. Since [my] hardiness temperatures are based on minimum temperatures each year, they are changing faster than the average temperatures,” Professor Krakauer said. He found that these lowest yearly temperatures warmed roughly two and a half times faster than the average temperatures.
His analysis also showed that the country is changing unevenly; more warming is occurring over the eastern interior and less in the Southwest.
