The invasion of the ‘tree snatchers’

Winter creeper (Euonymus fortunei) climbing a mature tree (left) and growing on the ground on Albemarle Street NW (right). (photo by Adam Sieminski)

by Adam Sieminski

Winter creeper (Euonymus fortunei) is a tenacious, perennial, and evergreen plant that grows as a sprawling groundcover or climbing vine. Those qualities make it attractive to many local gardeners – but the plant is invasive and damaging to trees. Introduced from Asia more than a century ago, this species is becoming a pest in the Forest Hills neighborhood as well as in nearby Rock Creek Park.

Five years ago, the Maryland Department of Agriculture named winter creeper a Tier 1 (the worst) invasive plant and forbade its propagation, sale, and transport. According to the Plant Conservation Alliance, climbing winter creeper outcompetes native vegetation by depleting soil moisture and nutrients. Vines on trees will continue climbing, and can eventually prevent photosynthesis and kill the tree.

Identifying and dealing with winter creeper early is important. The tiny aerial rootlets of winter creeper make it very difficult to pull away from the tree bark. Hand pruners can be used to cut the vines at chest height. Thicker vines may require a pruning saw.

Winter creeper leaves usually have a serrated edge that helps differentiate it from look-alike periwinkle (Vinca minor). Periwinkle can be troublesome too, by crowding out native plants, but is not on Maryland’s Tier 1 or Tier 2 lists. Periwinkle does not climb, and its leaves are not serrated. It has a delicate blue flower in the spring, in contrast to the white flowers of winter creeper.

Another plant with similar-looking leaves is Japanese spindletree (Euonymus japonicus). This one is used around the Forest Hills neighborhood in hedges since it grows as a relatively thick self-supporting shrub. It is not considered to be invasive and its hardiness makes it low-maintenance.

Japanese spindletree (Euonymus japonicus) is considered non-invasive. (photo by Adam Sieminski)

Casey Trees, a nonprofit organization established over 20 years ago to restore, enhance, and protect the tree canopy of Washington, is concerned about Euonymus fortunei. Nick Smalley, a field manager for Casey Trees, warned that winter creeper crowds out the native herbaceous layer and then can completely choke out trees.

“We recommend that it be carefully chopped off trees and completely removed wherever possible,” he said. “If volunteers are removing vines we normally just suggest what is called a window treatment, where you cut a one to two foot gap in the vine and leave the rest up in the tree to die. Pulling the vines out can pull down branches, living or dead, which can be a little dangerous depending on their size.”

Winter creeper strangles a tree.
(photo by Nick Smalley, Casey Trees)

Winter creeper is becoming a problem in Rock Creek Park. National Park Service botanist Ana Chuquin was clear: “Dig it up and dispose of it.”

“At this point, it’s not as big a problem as the porcelain berry vine,” said Chuquin, “but it is gaining an unwelcome foothold in the Park.”

Steve Dryden, Ana Chuquin and Angela Kramer standing near the Peirce Mill Orchard (photo by Adam Sieminski)

Steve Dryden and Angela Kramer, long-time directors for the Friends of Peirce Mill, have been certified as “Weed Warriors” by Rock Creek Park. This certification program, done in conjunction with the nonprofit Rock Creek Conservancy, provides individuals with the knowledge, skills, and techniques to help eliminate the threat of invasive plants in our region and act as stewards of parklands and natural areas in Washington. This fall, Dryden and Kramer will be leading a group of volunteers to clear out the winter creeper and porcelain berry (Vitaceae) that are growing to the west of the Orchard at Peirce Mill.

Another Weed Warrior often seen working in the Forest Hills neighborhood is John Burwell, who was just featured in this Forest Hills Connection Q&A. A retired professional photographer and now a certified Weed Warrior supervisor, Burwell has “adopted” the upper reaches of Broad Branch Stream as an area in need of help.

John Burwell examining mile-a-minute near Linnean Park. (photo by Adam Sieminski)

“Winter creeper loves to climb the mature trees that have rough bark,” said Burwell. “Invasives like porcelain berry and mile-a-minute love to climb on almost everything, and they seem to be particularly attracted to the cages we use to protect young trees from the deer.”

Both Burwell and Chuquin noted that the relatively slow-growing nature of winter creeper makes it easier, in some ways, to control. But left unattended, as Nick Smalley can attest, it can create a serious problem for our neighborhood trees. The experts agree that we should all be checking our tree boxes, yards, and gardens for winter creeper and getting rid of it.

Interested in becoming a Weed Warrior? The National Park Service, National Capital PRISM (Partnerships for Regional Invasive Species Management), and Rock Creek Conservancy conduct a two-part Weed Warrior training program. The first session is virtual and acquaints attendees with the basics of invasive species identification. This is followed by an in-person session to solidify that learning in the field. Email Katy Swiere (kswiere@rockcreekconservancy.org) to be notified of future training opportunities.

Or, join the September-October Weed Wrangle! Weed Warriors, in coordination with the above organizations, are leading invasive species removal events starting Saturday, September 9th and ending October 7th. To find opportunities and sign up to volunteer, visit rockcreekconservancy.org/rcc-weedwrangle.

Further reading:
Plant Invaders of Mid-Atlantic Natural Areas is a field guide and free PDF download. Or, order a print copy by emailing info@maipc.org.

Maryland Tier 1 Invasive Plants

Incised fumewort (corydalis incisa)
Winter creeper (euonymus fortunei)
Fig buttercup or lesser celandine (ficaria verna)
Shining geranium (geranium lucidum)
Yellow flag, pale yellow iris, water flag (iris pseudacorus)
Amur honeysuckle (lonicera maackii)

English ivy, another pest, climbing a tree. (photo by Adam Sieminski)