Plants know best: Does a new gardening map reflect climate change?
by Brett Buckner
brettbuckner@ymail.com
Mar 18, 2012 | 3399 views |  0 comments | 6 6 recommendations | email to a friend | print
Photo: Bill Wilson/The Anniston Star
Photo: Bill Wilson/The Anniston Star
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Deep in the night, or perhaps early in the morning of Jan. 25, Calhoun County moved … or rather “shifted” to use the proper idiom of those in charge of such things.

In fact, all of Alabama, as well as the entirety of the United States, shifted.

However, no seismic activity was recorded.

Truth be told, nobody much noticed at all, save for those whose job — or hobby — it is to know such things, namely America’s 80 million-plus gardeners.

This year, the U.S. Department of Agriculture released an updated version of its Plant Hardiness Zone Map for the first time in 22 years.

According to this $500,000 project, created in conjunction with Oregon State University, some things have changed — or returned to the way they were, depending on one’s perspective.

The map, which is used by gardeners to identify where particular plants will thrive, shows most of the country getting warmer.

But Calhoun County moved from zone 8a to 7b (with a sliver of the county remaining in 8b) — meaning that it’s getting colder in our neck of the woods, as our average winters dip down to 10-15 degrees.

Alabama, Florida and Georgia all trended slightly colder. This is largely due to researchers using temperature data from a longer and more recent time period. The new map uses data measured at weather stations during the 30-year period 1976-2005. The previous map, published in 1990, was based on temperature data from only a 13-year period, 1974-1986.

Some folks have proclaimed the map is proof of climate change. But USDA Agricultural Research Service spokesperson Kim Kaplan issued a word of warning: The plant hardiness map tracks weather, not climate, by looking strictly at average yearly lows, rather than overall temperature changes.

“It’s not a good instrument for trying to prove global warming,” Kaplan said. “It does not cover a long enough period. Climatologists like to talk in terms of a minimum of 50-100 years. We only have 30 years here.”

In truth, this latest map simply proves that the only constant for gardeners is change.

Zeroing in on Calhoun County

So what does this mean for the yard warriors of Calhoun County? Not much, said Hayes Jackson, urban renewal extension agent for the Alabama Extension Service.

These maps are something of a pet peeve for Jackson.

“They call it a ‘plant hardiness map,’ but that’s really misleading,” he said on a recent rainy afternoon that left him trapped in his office finishing paperwork. “We’re talking about an average winter minimum temperature … cold intensity. That has nothing to do with plant hardiness.”

Meaning the map doesn’t take into account duration or frequency of the cold weather.

“So you’re potentially basing your climate zone on one night of the year,” Jackson said. “As a plant person, that’s not a good thing.”

For Calhoun County Master Gardener Sherry Blanton, the release of the updated map doesn’t mean a whole lot, either.

“They can change it all they want, but I want to live through it first,” she said. “For us, I just don’t think it makes much difference at all. It’s really more about cold weather than it is about the heat. Heat does, of course, matter to plants — like rhododendron or lilac that really can’t stand our heat. But for us in Calhoun County, we’re not going to see a change in what can survive here and what can’t.”

The oleander warning

Sitting in a large pot on the back deck of Mindy Connor’s Oxford home is a long-dead pink oleander. Its intertwined trunk has numerous scratches and deep gouges where Connor used her fingernails to see if there was any green beneath the bark.

“But it was dead,” she said. “I knew it was dead, but kept holding out hope.”

There were other oleander planted in her yard — all of which were bought locally. They’re dead now, too. The oleander in the pot serves as a reminder of a lesson learned: Just because it’s pretty in the summer doesn’t mean it’ll survive through the winter.

“I remember being so excited when I bought them,” she said. “I went a little nuts, but they were blooming, and it made me think of the beach.”

Therein was the problem. Save for certain hardier types, oleander is recommended for USDA zones 8-10, and is most easily grown in warm, humid climates, like the Florida coast.

“I didn’t know that,” Connor said, laughing, “but I do now … and I’ve kept that one there to remind me to do more research on iffy plants, especially those I want to survive.”

There’s nothing wrong with pushing the envelope, with buying plants that may or may not survive zone 7b winters. Just be prepared to either haul them indoors or sit back and watch them die, depending of the severity of a particular winter.

“The plants will tell you what zone you’re in, not the map,” said Jackson, who loves blue spruce trees, although they can’t naturally tolerate the Alabama heat. “It’s a matter of survive versus thrive. I’m a survival champion, and I’m proud of the fact that I can get some plants to survive in areas where they aren’t supposed to live. But for the average gardener, that’s much more difficult.”

Connor was fortunate in that the half-dozen or so oleander she planted were in no particular arrangement — like a hedge or border — else she would have created what Jackson calls the “snaggle-tooth effect,” in which one plant is healthy and green while the one next to it is brown and dead.

“When you push the envelope in terms of hardiness, be prepared for some failure,” Jackson said. “Don’t build your design by creating formal rows, so that if some don’t survive you’re stuck with these huge ugly, dead gaps. Instead, just plant in more natural groups, so that if one or more don’t survive, it’s not such a big deal.”

Connor still loves oleander, but accepts that some just might not survive the winter. Instead, she’s sticking to local favorites such as crape myrtles, frost-proof gardenias, quince and dogwood trees.

“I think it’s probably time to throw away that other oleander,” she said. “I’ve got other plans for that pot. I’m pretty sure I’ve learned my lesson.”

Interest in tropical plants grows

As co-owner of Bloomin’ Miracles Nursery in Jacksonville, Victoria Dubose has noticed that more and more customers are willing to take a chance with plants that might not necessarily be zoned to handle Calhoun County’s occasionally harsh winters.

“Folks are getting the fever for tropical plants,” said Dubose, who owns the nursery with her husband, David. “They aren’t intimidated, even though there’s the chance they might not make it through the winter.”

As testimony to the unpredictability of nature and plants’ adaptability, Dubose points to two large windmill palms growing happily by the couple’s pool behind their house.

The windmill is a hardy palm and can withstand subfreezing temperatures, surviving in zones 7b-10 — putting it right on the border for Calhoun County. In its native habitat, this tough palm is sometimes subjected to a cover of snow and ice.

“During these past two record winters, it looked fabulous,” Dubose said. “It may have had snow and ice all over it, but it looked fabulous.

“And that’s the way plants are … they seem to always surprise you.”

Contact Brett Buckner at brettbuckner@ymail.com.

The gardening map

To view an interactive version of the USDA’s updated Plant Hardiness Zone Map, visit www.planthardiness.ars.usda.gov. The online map is searchable, including a “find your zone by ZIP code” function.
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