When you think of holly, images of holiday wreaths or landscaped hedges may come to mind. But did you know that English holly is an invasive plant, capable of colonizing the ground around it?

While walking the trails of the Whidbey Institute recently, Bill and I met Larry Rohan who is part of the Institute’s team of land stewards maintaining a healthy forest on the it’s hundred acre property. Late winter is the season that crews walk the trails pulling holly suckers and roots.

Larry Rohan grabs hold of invasive English holly with a weed wrench

Visiting the Whidbey Institute Feb. 16, David Welton photographed Larry Rohan using a weed wrench to remove holly roots and suckers.

English holly—unlike native American holly, which grows on the East Coast—is an imported landscaping plant, which grows into trees 15-50 feet tall and 15 feet wide. It can form an impenetrable thicket.

According to the King County Noxious Weeds site, which Larry referred me to, English holly is a “weed of concern…only causes harm when it spreads beyond its intended location and into natural habitats. It adds a dense evergreen tall shrub component to our forests that was absent before, changing the dynamics of the forest habitat. The year-round shade below the tree canopy and dense, thick growth allow holly to outcompete native plants and tree seedlings for space and resources. Once established, holly can form impassable thickets that are very difficult to remove. Wildlife (and humans) have a hard time passing through its matrix of hard wood and spiky leaves.”

Holly berries, while attractive, contain seeds which birds eat and distribute, contributing to colonizing of previous native plant growth

Anne Hayden keeps her eye on holly proliferation, and is one of the Institute’s long-time land stewards.

“About 20 years ago, I noticed where the holly was growing and let it know I’d be back in the right season to take it out by the roots,” Anne recalled. The right season is late winter. “One problem is they take over the forest understory. You have to appreciate the energy of holly. It is persistent, and has devised a number of ways to propagate itself.”

From Anne I learned ways holly colonizes the forest environment.

“One is by shoots coming up from the roots—suckering,” Anne explained. “If you cut a holly tree, the suckers will grow from the stump. They can grow 20-30 feet high on the Institute lands. You cut the stump and they come back every year. We cut all the suckers. The only way to remove the stumps is if you use chemicals (such as the herbicide imazapyr). Whidbey Institute is reluctant to use chemicals, so we go back every year and find the suckers coming up and cut them out to keep them from growing. Even if you cut the holly and lay it on the ground. It will grow.”

Holly trees if left unchecked will take over their surrounding area

Another way holly proliferates is through layering. A holly branch might rest on the ground. Before long, the branch will develop roots, which grow new suckers. Anne noted, “If a tree or large branch falls on a holly plant and knocks it to the ground, the holly will send roots into the earth where it makes contact with its own branches or stem.  A large bushy patch of holly grows this way, pinned down by a fallen tree.”

Birds—especially hungry robins in the winter—eat holly seeds, spit them out, and new holly forests begin.

Anne explained the way Whidbey Institute land stewards work with holly: “If they’re small shoots, we pull and pull until we get to the main stem. There can be 20 feet of roots. If they’re two inches or less, you can use a weed wrench, which pulls the holly out by its roots. It’s so satisfying to pull out.”

Whidbey Institute Land Steward Larry Rohan uses a weed wrench to pull holly roots

For roots three inches or more, the crew cuts the suckers growing from them each winter.

“We keep doing that until the life force is knocked back enough in that it doesn’t grow well,” Anne added. “We’ve kept it from being a problem.”

Whidbey Institute Land Steward Larry Rohan sent this photo of the weed wrenches used for keeping holly proliferation in check.

Holly’s proliferation throughout western Washington state has cost taxpayers at least $120,000 in holly removal at St. Edwards State Park and Lake Youngs, a reservoir in King County.

In the December 2023 issue of High Country News, the cover story is “A festive plants runs amok.” The article notes that holly growers lobbied the state to delay holly’s listing as a ‘noxious weed.’ Yet holly threatens native plant growth. In the mean time, land stewards such as Anne, Larry and their team, work to keep holly’s growth in check by their winter pruning and root pulling.

If you are interested in learning more about the invasive species that are impacting the forest, or want to get involved with removal efforts, contact Larry Rohan at:  larryrohan@whidbeyinstitute.org

In addition, if you wish to comment on having holly listed as an invasive plant, visit this link for Washington State noxious weed control.

The way Larry Rohan likes to see a holly tree–cut down as a Christmas tree. Photo shared by Larry Rohan
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1 Comment

  1. Dianne M Iverson on

    one effective way i have found to eliminate the big holly trees after taking down the tree, is to drill holes into the stump and pour salt crystals [which they sell at the Country Store] … into the drilled holes and across the top of the stump, and then cover it. I don’t like using plastic so I put a small upside down cardboard box over it, weighed down with rocks. Salt is not the best thing for the environment either, but it is way better than chemicals.

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