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Poison ivy, unholy holly, and lax weed laws

Walls of holly. Credit: Eric Scigliano

Spring has finally sprung, and green-thumbed Northwesterners have emerged to till the soil, fill the pots, plant the seeds — and see how far the ivy has climbed over their yards and up their trees. Some will whip out their trowels and plant elegant new ivy vines to decorate their gardens and drape their rockeries. Thousands more will dust off the pruning shears and set to cutting back vines and ripping out roots, trying to restore some shreds of the original, pre-ivy Northwest forest.

“English ivy,” as it’s commonly known, is the super-athlete of weeds, a rock climber, high-jumper, and cross-country runner able to top tall trees and smother entire landscapes. A single plant can put out a ton of leaves and vines, heavy sails that conspire with the wind to tug tall trees down.

On the ground they form opaque mats, suffocating every other sprig and bush. The result: A lush, sterile monoculture. Though it feeds a host of insects and other critters in its European homeland (and is in turn controlled by them), ivy is inedible — even toxic — to most American critters. But rats nest happily in its protective blanket, and a few birds — starlings, jays, robins, waxwings — eat its purple berries and spread the seeds, sending it far afield.

English ivy is a disarming nemesis. it makes brick walls, rock faces, even forest floors look serene and elegant. It’s been cultivated for centuries and bred into hundreds of ornamental varieties. It is decked in glamorous cultural associations: the ivy wreaths worn by Greek gods, the Ivy League itself. “Doctors bury their mistakes,” Frank Lloyd Wright supposedly said. “Architects cover them with ivy.”

But it’s a stealth killer, patiently waiting for decades before spreading. European immigrants brought it to the Northwest in the nineteenth century, and it remained docile in their gardens. “I’m told it never seeded for a century or more here,” says Tom Wessels, the Washington Agriculture Department’s plant services manager. 

Blame climate, adaptation, or some sort of critical mass; in the 1980s, it erupted. Arborists and conservationists decry the transformation of living forests into “ivy deserts.” Since 2005 the City of Seattle alone has expended more than $11 million ($8 million in public funds, $3 million from Forterra, formerly the Cascade Land Conservancy) plus 400,000 hours of volunteer labor removing invasive plants, mainly ivy, from its parks. The Seattle Parks Department calculates that it costs about $25,000 to restore an acre of forest and $800 a year to maintain it.

Meanwhile, nurseries and big box stores continue selling ivy here in Seattle and everywhere else in ivy-draped Western Washington — quite legally, if not wisely. In 2002 Washington state listed three cultivars of English ivy (Hedera helix) and a similar species, Hedera hibernica, as Class C noxious weeds. Unfortunately this listing carries no force on its own, though it can empower counties to act.

“Class C” applies to weeds that are deemed so widespread there’s no hope of eradicating them. King County “recommends” that landowners and others avoid spreading them, but doesn’t stop nurseries from doing just that.

Two considerations underlie the decision not to “quarantine” (i.e., ban) ivy. First, only a small share of the available ivy varieties have attacked local woodlands, according to a DNA study led by botanist Sarah Reichard, the resident invasive-species expert at UW’s Center for Urban Horticulture. Most samples were actually similar species, Hedera hibernica, a.k.a. Atlantic ivy, which grows in coastal Europe, where the climate resembles ours. The rest consisted of a few helix (English ivy) cultivars.

Still, it’s not clear why these ivies are the only ones to break out so far. Were they merely the first ones imported and widely planted? Will others run rampant in another century, or decade? Hedera algeriensis, a bicolored species that’s deemed safe and increasingly popular, grows profusely in its North African homeland.

Many other cultivars resemble the problem varieties, says Sasha Shaw, the King County Noxious Weed Control Program’s educational specialist. “It’s very difficult to tell which cultivars you have without a DNA test, so it would be difficult for nurseries to avoid selling them.” In short, if you’re going to let them sell any ivy, you might as well let them sell it all.

The other reason officials have held back on banning ivy sales is commercial. The Washington State Noxious Weed Control Board chooses which plants to list as invasive, but the Agriculture Department determines whether to ban their sale and order their removal. And its mission is to promote agriculture, not to preserve wilderness.

“We cannot pass any rules without considering the impact on small businesses,” says Ag’s Tom Wessels. “The legislature requires that. There’s a lot of small mom and pop nurseries that are selling ivy . . . You see people at farmer’s markets that make these topiaries of ivy.”

But if they weren’t selling ivy, they’d presumably sell other plants in its place; several unrelated species are even called “Swedish ivy” and so on. Still, as Shaw says, “it’s a lot easier to quarantine a plant if there’s no market for it.”

The market prevailed last year when, at King County’s urging, the weed board debated whether to list another European import, English holly, as a Class C noxious weed. Holly, like ivy, comes wrapped in lore and nostalgia, and it’s probably more commercially important than ivy; with their congenial climates, Western Washington and Oregon are a sort of Holly Belt. Commercial growers ship it — mainly in the form of wreaths and Christmas decorations — around the country.

But that same climate, plus berry-eating birds, also enables holly to run wild. Like ivy, it seemed to lie quiescent for many decades. “Lately,” says Shaw, “it’s really taken off.” Like ivy, it grows in the forest shade, choking out understory plants and forming razor-wire-like barriers. Unlike ivy, it roots deeply and, as anyone who’s cut down a holly tree knows, is nearly unkillable; stumps and root remnants keep resprouting. No wonder holly’s a symbol of resurrection and immortality.

The listing would only have been advisory, and would have exempted holly farmers. But they still rallied against it, throwing everything but the kitchen sink into the argument. “The [noxious weed] connotation itself gives us a bad name,” the president of the Northwest Holly Growers Association told the agricultural website Capital Press. “I think it will destroy us [by turning off buyers].”

If holly were invasive . . . it would have covered the entire region by now,” one Olympia holly farmer reportedly contended. “We growers don’t see our orchards spreading. We propagate by cuttings, not by seeds. This is a localized problem in suburban areas, and it’s laid at the feet of farmers who are already stretched. Should we be responsible?”

The holly trees cropping up around King County were merely sprouts from old orchards, another farmer declared. Blame the county’s “mismanagement” of development on those sites.

I didn’t realize my little yard in Seattle, and the one I occupied previously, were once holly orchards. Every year I pull up new crops of seedlings. Likewise the uninhabited island in the Skagit Delta I paddled to a while back. I saw a few young holly bushes, pulled them up, and then realized the effort was beyond me; they’d sprouted everywhere.

The growers’ botanical claims may not have been persuasive, but the weed board realized it didn’t have enough scientific data to confirm widespread observations like those and perform the required risk assessment on holly. So it declined to list it as noxious. At the same time it rejected the growers’ request to permanently exempt holly from the listing.

King County is now awaiting results from a pioneering study of holly’s impact on a representative, relatively intact chunk of local forest, Saint Edward State Park near Bothell. Its author, UW biologist David Stokes, will present results and offer an agenda for further research. Preliminary findings: The speed of holly’s spread is “increasing exponentially.” It “has the potential to become a dominant species both in number of individuals and area covered within a few decades.”

For now, keep pulling up those sprigs. And compare Washington’s light-handed approach to invasive plant regulation with Oregon’s. The two states apportion this effort differently: Washington’s is more decentralized, and all its counties have their own weed control boards. But the Oregon Agriculture Department’s noxious weed program has a much larger staff — 18 members, including six regional offices — and is unafraid to crack down harder, even on a widespread, popular plant.

Oregon hasn’t formally considered listing holly yet, though “some people would like us to,” says Tim Butler, the Oregon program’s manager. “We haven’t seen that kind of impact yet.” So Oregon will wait and watch how the holly behaves, which is pretty much what Washington’s doing.

On ivy, however, Oregon seems to have embraced the view that it’s never too late to try to roll back a botanical invasion, and any new introduction of an established pest only adds to the problem. It responded in opposite fashion to Washington to the question of how to ban the aggressive cultivars when they’re so hard to distinguish from the others. In 2010 it extended an earlier ruling and banned the sale, transport, and propagation of all cultivars of English and Atlantic ivy, in all forms.

“Some of the growers had concerns,” says Butler. “The biggest came from folks that use it in ornamental baskets, topiary, and floral arrangements. We allowed that for a period of time.” Mom and pop evidently adapted to using other plants.

Portland’s crusading No Ivy League played a big part in persuading the state to take such stern measures. Its counterparts in Washington are trying to persuade gardeners to avoid planting ivy and even rip it out, and get nurseries and other retailers to sign a pledge not to sell English ivy, especially the four notorious varieties. It places those who comply on an “Ivy Free” list of recommended nurseries.

But at least two on that list, Swanson’s Nursery and City People’s Mercantile, affirm that they do sell ivy, though apparently not the four no-nos. “We have lots of ivies,” one Swanson’s staffer told me. “We don’t carry the regular English ivy — the obnoxious one, the one that spreads.” With the letter of the pledge ambiguous, they’re at least complying with the spirit.

That’s more than you can say for many big-boxes and supermarkets. “One Home Depot said they would stop,” says Shaw, “but with so much turnover in management they can’t keep track.” Tom Wessel notes that plants commonly “lose their identity” as they move along the nursery-wholesaler-broker-buyer-retailer chain.

Maybe that’s what happened on the way to the Queen Anne supermarket I visited. Little pots of dark-green ivy — which, as far as I could tell, could be the dreaded Hedera hibernica — lined an outdoor shelf. They were not labeled, not even as ivy. The young woman tending the plant section had no idea what they were.

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