Ivy is perfectly picturesque when growing in the English countryside or climbing the hallowed walls of Cambridge.
But here in the Pacific Northwest, ivy is a bully. A tree-killing, rat-infested, bird-poop-traveling bully.
KUOW listener Emma Johnson wanted to know: "What would Seattle look like if English ivy was left to grow without check? Would any trees survive? And how did ivy get here?"
We asked Nelson Salisbury, an ecologist at the conservation group EarthCorps, which regularly coordinates volunteer ivy-pulls around Seattle. He said English ivy—and the Irish or Atlantic ivy varietal to an even greater extent—has grown into a huge problem for the region. The invasive plants suffocate and weigh down trees. They squelch young plant life by blocking the sunlight from reaching the ground. And if left unencumbered, they create ivy deserts—where no other plant life thrives.
So what would Seattle look like if invasive ivy was allowed to grow unchecked?
“It’s not that hard of a question,” Salisbury said. “There are examples of it right now. If you go and look at certain parts of the city that are heavily invaded by English ivy, that’s what I think our forests would look like.”
The greenbelt on the eastern slope of Queen Anne is a particularly troublesome area, as is the West Duwamish Greenbelt in south Seattle.
“I think there is a very real scenario to suggest that without active management, our forests would all become invaded by English ivy,” Salisbury said.
Whether the vines would eventually topple all trees is difficult to say; there are too many variables in that hypothetical. But Salisbury noted that invasive ivy has been in the region for only about 100 years. A survey conducted before conservation work started 15 years ago estimated that roughly 10 percent of the city’s 8,000 acres of public land were infested with invasive ivy. Only the Himalayan blackberry plant (with its own strange, twisted history) was more prevalent.
“If we gave it another hundred years, I would imagine the invasion would accelerate,” Salisbury said. “Originally there were only a few plants, and they were able to spread to this huge area.”
If this is the first you’re hearing of ivy’s bad reputation locally, you’re probably confused. After all, ivy is everywhere right? How can it be bad?
For starters, ivy is everywhere. It thrives in the Pacific Northwest’s mild climate and can grow in sun or shade. And since it’s not native to the region, it doesn’t have the environmental checks and balances it has in western Europe where it originated.
Rats are drawn to ivy because it helps them hide—and climb. And when invasive ivy crawls up trees, it weakens them by blocking sunlight and adding weight, meaning the trees are more likely to topple during windstorms.
Alison Halpern, executive secretary at the Washington State Noxious Weed Control Board, said the ivy removed from one tree in the Olympic National Park weighed in more than 2,100 pounds.
Ivy grows fast, spreads faster and can live for hundreds of years. The plants produce ripe berries in the spring (instead of the fall like many native plants), and birds flock to them. But the berries’ seeds are pooped out—often in forests and parks—which is how ivy escapes from yards.
This brings us back to the second part of our listener’s question: How did English ivy get here?
“It came from our backyards,” Salisbury said. “It escaped cultivation. In order for us as a city to really get English ivy to become less of a problem, it is definitely going to mean controlling it in our own backyards.”
English ivy was brought to the United States by colonial settlers who craved the aesthetics of European gardens. Halpern said the earliest record of English ivy in the Pacific Northwest dates back to gardens of the 1890s. Even now, it tends to plague residential areas.
“The biggest ivy problems are in areas that are urban or suburban,” Halpern said. “There is some ivy on the Olympic Peninsula, particularly where there were homesteads.”
English ivy is also a problem for large swaths of coastal North America. Volunteers have waged war with it in Vancouver, B.C.’s Stanley Park. Salisbury said he’s seen invasive ivy snaking up trees in California’s redwood forests. It poses a threat to native plants in Washington, D.C.’s National Arboretum. And Oregon banned the sale of English ivy in 2010.
Halpern said a quarantine has been debated for Washington state, but it would be difficult to implement because there are over 300 cultivars of English ivy, and only some are invasive.
“From a regulatory standpoint, it’s a nightmare,” she said.
For now, Halpern plans to work with nurseries to voluntarily halt sales of problematic varieties.
“With Oregon quarantining it, it could really help us to make that push,” she said.
So what’s to be done? Your assignment is this: Take a good, hard look at the ivy growing in your yard or neighborhood. If it looks like this (and chances are, it does), then it has to go. You can pull it out of the ground by the roots and clip vines near the base of trees if the ivy is growing vertically.
Halpern recommends leaving the plants on a tarp or cement area until it turns brown, then disposing of it in the garbage—not in your compost bin. She said herbicide can be used as well, but you may want to consult your county’s noxious weed board first.
It might sound like a daunting task, but Halpern said it’s worth the effort.
“It can be really therapeutic,” she said. “It’s a nice physical workout, and you can see the results. You see trees living and breathing again.”
Correction 7/8/2017: Earlier photos published with this post may not have shown an invasive species of ivy, but rather a more decorative type. To be safe, we removed those images, pretty as they were, and have replaced them with those above.
Submit questions about our region in the form below. Your question could be investigated in a future KUOW story.