Be wary when gardening with non-native plants

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By VIRGINIA A. SMITH The Philadelphia Inquirer
PHILADELPHIA -- It's pretty, colorful, tall and tough. So how come Dale Watsonhates purple loosestrife?
Scratch that. She doesn't hate it. She's upset that she still seesso much of it. Though beautiful, purple loosestrife ("Lythrumsalicaria) is considered a noxious thug that grows fast, spreadsfar, and obliterates everything in its path, especially alongwaterways.
"Purple loosestrife is so destructive. It's really bad," saysWatson, a social worker from Goshen, N.J., who isn't shy aboutconfronting anyone buying, selling or planting it in her homestate, where it's still legal.
Watson's intensity is stoked by the knowledge that hyper-aggressiveplants like purple loosestrife - usually called invasives, alsoknown as aliens or exotics - are a major problem nationally andglobally. They can destroy whole ecosystems and cost millions ofdollars in economic losses and remediation.
To home gardeners, that may seem a faraway problem. After all, whatdifference could one or two problem plants make in, say, a smallbackyard in the city?
"Birds still come to the city and take seeds to parks. They don'tknow they aren't supposed to do that," says Bill Lamack, nurseryand grounds manager at Bowman's Hill Wildflower Preserve in NewHope, Pa.
Perhaps gardeners need to think of invasives the way Americans arefinally thinking about energy: One person's gasoline consumptionmay not be much in the scheme of things, but it all adds up.
First, though, we have to ask: What, exactly, is an invasive? Isit, as so much of the literature posits, a plant that's outside itsnative habitat?
Not necessarily. Though "invasive" and "nonnative" are often usedinterchangeably, not all nonnatives are invasive and vice versa.
"Just because a plant is from somewhere else doesn't automaticallymean it's a problem," Lamack says. "There are plenty of exoticspecies that are well-behaved in the garden."
And some native plants make lousy neighbors: Rogue seedlings ofnative trumpet vine "(Campsis radicans) can drive a gardener mad.
"It really does boil down to, on the individual level, how much ofan impact is this making?" says Michael Pollock of the New JerseyAudubon Society. "We tag something as invasive when it's atremendous pain. For home gardeners, that means 'this thing justwon't go away.' "
But "aggressive," "vigorous," "super-hardy" and "fast-grower" arenot the same as invasive, according to naturalist Pat Sutton ofCape May Court House.
"Quite a few of the gardeners I interact with are passionate aboutwildlife gardening, but they're not necessarily botanists," shesays. "They'll start calling things that are vigorous invasive.They're not invasive. They're just aggressive."
Blue mistflower ("Conoclinium coelestinum) found a perfect match inthe moist soil of Sutton's garden. "Now, it wants to be everywhere,and a lot of my other plants are getting crowded out," she says."I'm weeding out this beautiful native wildflower that I lovebecause it's so aggressive."
But she doesn't consider it invasive. "It's a native that, in somesituations, becomes aggressive," Sutton explains.
Not to further fuzz up the discussion, but what's a "native"? Aplant that was growing in North America before the white man came?Whose home turf is Pennsylvania or New Jersey? Conversationally,it's often "a plant that's from here" as opposed to "from somewhereelse."
"I tell students what's native at the bottom of Mount Nittany isn'tnative at the top. You change elevation, and what's nativechanges," says Larry Kuhns, professor emeritus of ornamentalhorticulture at Pennsylvania State University.
Purple coneflower ("Echinacea purpurea) is a wildly popular "NorthAmerican native," but its native range actually runs from Ohio toIowa and south to Louisiana and Georgia. Not exactly "from here,"if you're from here.
"It's tricky," Kuhns says.
Many invasives arrived in this country by accident, their seedsembedded in soil used as ballast or in packing material aboardships. European settlers and subsequent generations ofinternational travelers and traders also brought "exotic" plants tothis country for their culinary, medicinal or ornamentalproperties.
"So many of the things we pull our hair out over, somebody broughtover on purpose," says Art Gover, research-support associate forhorticulture at Penn State. (That includes purple loosestrife, aEuropean import in the 1800s.)
Freed from the pests and problems back home, some of these plants -especially the ones that are tough and highly adaptable, produceabundant seed, and reproduce quickly - took off unchecked in theirnew environment.
Sounds like tree-of-heaven (Ailanthus altissima), which notoriouslysprouted from the upper floors of Philadelphia City Hall in thenot-so-good old days. "It eats cities alive," Gover says.
But it was not always so. Tree-of-heaven came from China to Europeto John Bartram's garden in Philadelphia.
"It was this curious plant from Asia, and the idea was, hey, thiswill grow anywhere," Gover says. "In the Industrial Revolution, wecan grow this in these dirty, smog-laden cities in stuff that isn'teven soil."
Today, you can practically watch it leap out of sidewalk cracks."You think, 'Who would want that?'" Gover says, "but it wasintentionally introduced."
Intention, then, is key to managing the invasives problem, and JimMacKenzie, of the Pennsylvania Landscape and Nursery Association,says the industry is working to "look at the species of concernthat are out there and to try and pull those and work those plantsout of production."
MacKenzie, president of Octoraro Native Plant Nursery, concedesthat there are "some places out there that don't care and stillsome plants in the trade that are problematic."
But more nurseries are trying to educate consumers about plantchoices and selling more natives, he says.
Even so, New Jersey crusader Watson is discouraged to see purpleloosestrife all over Cape May and places like the Hereford InletLighthouse in North Wildwood.
"It seems everybody is selling it or growing it," she says."They're wearing me down."
The National Arboretum in Washington divides invasives into threebroad categories:
-Danger! Don't plant it. Things like purple loosestrife.
-Warning: If you see it, remove it. Things like tree-of-heaven,garlic mustard, lesser celandine.
-Caution: It's not a problem if you manage it wisely. Things likeEnglish ivy, butterfly bush and the common daylily.
Forty-six states, including Pennsylvania but not New Jersey, havedesignated certain plants as "legally noxious," meaning it isillegal to buy, sell, transport or plant them. Pennsylvania hasidentified 14 major problems, such as purple loosestrife,multiflora rose and kudzu. You can find them athttp://www.invasivespeciesinfo.gov/. Other state lists, witheducational but not legal import, include more ornamental plants ofinterest to home gardeners.
Here are some of the troublemakers:
Shrubs: Japanese barberry and spirea, Tartarian honeysuckle,privet, Viburnum dilatatum and sieboldii, burning bush (Euonymusalatus). Of the latter, Cheryl Bjornson, an invasive-plant expertwith the Chester County, Pa., Cooperative Extension says, "Thebirds eat the seeds, they get dropped in the woods, and there'sburning bush everywhere. People love its red color in the fall, butit just shouldn't be sold."
Trees: Norway maple, Siberian elm, empress, Callery pear.
Vines: Chinese and Japanese wisteria, Japanese honeysuckle,five-leaf akebia.
Groundcovers: vinca, pachysandra.
Ornamental grasses: maiden grass, running bamboo.
"This is all a learning curve," says Bjornson, who battles trumpetvine in her garden and chides herself for planting it years ago. "Icouldn't believe I made that mistake," she says.
You can tear out your mistake, which may take repeated tries, andeventually, you may need to finish the job with a strong, targetedherbicide.
Then choose from a long list of well-mannered, attractivealternatives to those erstwhile rowdy plants. For example, you cansubstitute native plants like American wisteria for the Chinese orJapanese varieties, anise hyssop or liatris for purple loosestrife,sourwood tree for Callery pear, red or black chokeberry for burningbush.
For information, check out Bowman's Hill Wildflower Preserve athttp://www.bhwp.org/, Native Plant Society of New Jersey athttp://www.npsnj.org/, or Brooklyn Botanic Garden athttp://www.bbg.org/.
And take a page from Dale Watson, who's on a tear about purpleloosestrife: Speak up when you see bad stuff in a nursery orgarden.
"I love all plants, and I love all gardens," she says, "but I don'twant to contribute to hurting the environment."