Northern Shenandoah Valley shows little change in revised plant hardiness map
Editor's note: This is the first in a two-part series on the local effects of the newly updated USDA Plant Hardiness Zone Map. Saturday: How winegrowers are reacting to the changes.
By Alison Laurio -- firstname.lastname@example.org
STRASBURG -- Virginia, some say, has a Goldilocks climate.
"It's not too cold, and it's not too hot," said Janet Heishman, owner of Gabalot Gardens, 373 Green Acre Drive.
The U.S. Department of Agriculture's new version of its Plant Hardiness Zone Map, the first revision of its official guide for the nation's some 80 million gardeners, shows a general warming trend.
Nearly entire states, including Ohio, Nebraska and Texas, are in warmer zones than in 1990, when the prior guide was released. That was not the case in Virginia, where most changes were slight.
For many whose business here is in the outdoors, the trend is clear.
"It's warmer," Heishman said. "When you're outside for the majority of your days, you see that something has changed. We've noticed it, and a lot of our customers have noticed it.
"A lot of people come in and they're worried because things have been so mild. I think we'll be OK, because the nights are still cold."
The zone map, commonly printed on the back of many seed packets, considers only average lows.
"Cold is usually the limiting factor for most perennials," said Kim Kaplan, spokeswoman for the Agricultural Research Service at the USDA and a member of the map development team.
The new map's designations represent the average annual lows based on data from 1976 to 2005. It replaces a map from 1990 based on data from 1974 to 1986, she said.
The USDA for the first time used algorithms that considered factors including changes in elevation, closeness to large bodies of water and position on the terrain -- like valley bottoms and ridge tops.
An interactive version is available at www.planthardiness.ars.usda.gov, and by typing in your ZIP code, you can get the climate data for your neighborhood.
In the Northern Shenandoah Valley, where most areas are zone 6A (minus 10 to minus 5) or 6B (minus 5 to zero), the map shows small pockets that are a bit warmer or colder, but "many places did not change," Kaplan said.
The changes may be from the map's accuracy, its scale or the addition of new weather data, she said.
Comparing more years of data makes the map a more powerful tool, said Alex Niemiera, associate professor in Virginia Tech's Department of Horticulture who teaches woody landscape plants and the lab for nursery production and marketing.
"I think the main impact of this map is it gives gardeners and landscape professionals more information about their local environment," he said. "It's giving us more power to make choices.
"Gardeners could cheat a little bit and grow plants that previously would not grow well."
Some crepe myrtle varieties, for example, might grow here in a climate that's a bit warmer, Niemiera said.
Heishman said warmer weather has led some plant lovers to experiment with crepe myrtle and with salvia, which has some less-hardy varieties.
"They're making it," she said. "Verbena grows everywhere along the coast. Up here, it teeters. And Shasta daisies. Up here, they're real borderline. I think the warming opens it up for people to experiment."
Other garden favorites that might start doing well are herbs like lavender, rosemary and thyme, Heishman said.
She is even experimenting with a hardier single-flower camellia.
The New River Valley was zone 6A and now is 6B, and Niemiera said some cool season crops may or may not be affected, but "there is some data to show that particular species might thrive under warmer temperatures."
Some are not beneficial.
"For example, the Japanese honeysuckle is a terrible weed species throughout the eastern U.S., Niemiera said. "Warmer temperatures favor it having more growth potential, having more invasive potential."
Diseases and fungi also may relocate.
"We're looking at diseases moving up the coast," said Heishman, who noted the spotted wilt virus that ruined many tomato crops a couple of years ago. "They say you should buy plants that were started where you are gardening."
Niemiera said products from the nursery industry are widely distributed when sold to big-box stores.
"Mass merchandisers have been and continue to offer in a big regional sweep," he said.
Started in the South, many are unsuited to grow in some of the other areas they are shipped to for sale.
That is how the tomato virus came into our area, Heishman said.
When it comes to growing weather, it's the warm temperatures that bother her.
"I don't worry about the winters," she said. "I think people need to be more worried about the heat. That's where I think climate change is seen, and I don't think it's a cycle."
It has affected her business. Two years ago when temperatures were in the hundreds, "we shut it down in the afternoon," Heishman said.
And customers are wanting plants sooner.
"It's just an earlier start for us," Heishman said. "Instead of May 10th to 15th, we try to be ready May 1st. It makes us crazy in here because we have to plant seeds. People come in in April and want to know why we don't have tomato plants."
Last year, her husband, Ron, counted the tomato plants they grew for sale -- 17,000.