Palm trees popping up in Knoxville? Sub-tropical flowers thriving in Pennsylvania? Mangoes aren't growing in Manhattan yet, but it may be a bizarre glimpse of the future.

The New York Times, which has been tracking the impact of climate change on American life in their Warming Trends series, reports that the subtropical plants are marching north.

As a result of global warming, gardeners are starting to grow plants in their backyards that would never have survived the winter a decade ago. In fact, the native flora and fauna that we use to define parts of country is changing right before our eyes.

It's wreaking havoc with the nation's plant hardiness zones -- the system gardeners use to figure out which plants can handle which climate. Gardeners are on the front-lines of the shift (and have been for years) seem to have been the among the first to notice the differences. If you've got a green thumb, download the Gardeners' Guide to Global Warming file posted at the National Wildlife Federation website.

The option to grow subtropical plants is good news for people who've always dreamed of a palm tree in their backyard. But, of course, there are a lot of downsides as these eco-systems change. For instance, warmer temperatures also mean people can expect new and different pests. The carbon dioxide from greenhouse gases cause poison ivy and invasive vines, such as kudzu, to grow much more aggressively.

And, perhaps the real shocker is that state flowers, such as sunflowers in Kansas or magnolias in Mississippi, may become obselete. According to the National Wildlife Federation, 28 states will no longer be able to grow their official state tree or flower by the end of the century.

The article reminded me a conversation I had a couple years ago with very helpful guy at my local nursery. I wanted a xeric shade tree for my patio, and he directed me to a Mexican Buckeye.

The tag made one thing clear: This species was zoned for balmy Dallas, not the much colder high deserts of New Mexico. But the nursery guy just told me to ignore the plant zones.

"It'll be perfect," he assured me confidently. "It wouldn't have made it 20 years ago, but they do great out here now."

Turned out that he was right. That little tree is thriving and should reach maturity in about eight years. I just hope that I won't be growing bananas and coconuts in my backyard by then.