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.
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