Not so jolly invader: English holly spreads across Northwest forests

Deep in the woods, Kevin Zobrist finds thickets of English holly growing underneath towering fir trees.

The prickly shrubs - with their glossy leaves, scarlet berries, and Yuletide associations - aren't a jolly sight for Zobrist, a Washington State University Extension forester. Since holly was introduced to Western Washington more than a century ago, the horticultural invader has infiltrated wetlands, conquered parks, and marched through suburban and forested landscapes. In natural settings, the holly crowds out native plants, reducing forest diversity and degrading wildlife habitat.

"It's up there with Himalayan blackberries as one of the most prolific invasives we deal with," said Zobrist, who helps landowners learn about forest management strategies. "It's rare that I visit a landowner and we walk through their forest without finding holly."

Like many invasives, the festive holly used to deck European halls (Ilex aquifolium) got its start here through intentional plantings. The state's first commercial holly farm was established near Puyallup in 1891, and a Northwest holly industry continues to ship fresh greens throughout the United States.

But holly's spread can also be traced to Seattle socialite Lillian McEwan, who led a push to designate Washington as "the Holly State" in the 1920s. McEwan sought to beautify Western Washington forests by adding English holly, a centuries-old symbol of Christmas cheer and winter solstice celebrations.

"She envisioned a state where there were hollies in every forest and along every roadside, invoking that holiday spirit year-round," said Rahel Stampfer, acting program manager for the King County Noxious Weed Control Program.

Although McEwan failed with the "Holly State" moniker, other parts of her campaign were a runaway success. The wife of a prominent lumber executive and the founder of the Seattle Garden Club, McEwan recruited school children to plant holly in local parks. In 1928, Girl Scouts planted 1,500 holly seedlings on Arbor Day in Seattle's Seward Park.

Similar planting projects took place in other communities. Over a decade, an estimated 30,000 Western Washington children planted holly in their local parks and forests.

With no natural enemies and a conducive climate, English holly took root in every county west of the Cascades. The dense holly thickets are the result of underground runners that create colonies similar to aspen groves. Birds also help propagate new holly starts.

"Robins, in particular, love holly trees," Stampfer said. "They'll gobble up the berries produced by the female holly trees and spread the seeds over a considerable distance."

Once established, holly is hard to eradicate. "Studies show that left unchecked, holly will spread at an exponential rate," Zobrist said. "It will completely take over the forest understory."

Even chainsaws are no match for holly. "Cutting it down can make it worse. You'll end up with dozens of new holly sprouts from the trunk and the roots," he said.

When Zobrist visits landowners, he takes along an EZ-Ject Lance and cartridges filled with the herbicide imazapyr. Injecting the cartridges into the cambium layer between the bark and the wood of the trunk kills the holly with minimal impact to the surrounding environment. Since the lance and cartridges can cost $1,500 or more, Zobrist said neighbors sometimes chip in to buy the tools and share them, he says.

Becky Chaney has been fighting holly on her four-acre property near Carnation for about 30 years.

"It's pretty common in my neighborhood for people to think of holly as being desirable," said Chaney, who chairs the King County Noxious Weed Control Board and previously worked as an environmental consultant. "Holly is one of those invasives that lingers in the background. By the time you notice them, they're pervasive and hard to control."

Through constant vigilance, Chaney has been successful with mechanical removal on her property. Young holly starts are removed by hand. She trims back the branches on established hollies, weakening the trees until she can dig up the taproot.

In Washington, there are no requirements for controlling holly on your property. WSU Extension, the King County Noxious Weed Control Board, and other organizations instead work on educational efforts. That can include helping people recognize holly starts in their local park, understand best practices for its removal, or even re-think holly in their own landscaping.

"When someone has a beautiful holly tree that's the centerpiece of their front yard, removing it can be a hard decision," Zobrist said. "But there are so many good native alternatives that are also beautiful and provide berries that attract birds and wildlife."

Some of his favorite landscaping plants include native hawthorn, elderberry, Pacific rhododendron, and-of course-conifers. Pacific madrones, a broadleaf evergreen with reddish bark and red berries, also provide Christmas colors.

And if glossy, deep green leaves are a draw, consider planting a native Oregon grape. While the berries are blue, the prickly bush might just be the Northwest's answer to English holly.