From philly.com:
The scientific evidence suggests spring arrives sooner across the United States, expanding the growing season. That is something the National Phenology Network, based in Arizona, has begun monitoring closely.
The expansion has not been linear, said Deke Arndt, a researcher at the government’s National Climate Data Center in Asheville, N.C. “Not all places have been seeing longer growing seasons,” he said. But the Mid-Atlantic region has.
On average, he said, the U.S. growing season has expanded about two days a decade since the end of World War II.
That’s the result of later first freezes in autumn and early winter, and earlier last freezes in late winter and spring.
What’s behind the trend? Probably the obvious.
All rhetoric, emotion, and politics attending climate change and its causes aside, the Earth indisputably has warmed subtly in recent decades. That is verified by surface and satellite observations, with the warming concentrated in the Arctic.