Oregon Grape | Keweenaw Invasive Species Management Area (KISMA)

Mahonia aquifolium

Characteristics

Oregon grape, a woody shrub in the Barberry family, Berberidaceae, is an understory invasive that prefers partial shade and moist, yet well-drained soils

typically grows 1-5 feet tall, spreading outward with time
yellow flowers bloom sometime around May and develop into clusters of dark blue "grapes"
identifiable in winter as the leaves are evergreen, yet they tend to take on a red or purple color in the colder months
compound leaves are glabrous, and individual leaflets are dark green in color with pointed spines that resemble holly

Another key identifying feature is the yellow pigment found within the roots of all Berberidaceae plants. For more information visit Midwest Invasive Species Information Network (MISIN).

Oregon grape with yellow flowers — Yellow flowers of Oregon grape

Image credit: MISIN

Oregon grape with purple fruit — Purple fruit of Oregon grape

Image credit: MISIN

Oregon grape invading wooded area — Oregon grape escaped into the forest

Image credit: Sigrid Resh

Oregon grape with red leaves — Oregon grape with red foliage in the winter

Image credit: Sigrid Resh

KISMA Management Practices

Luckily, Oregon grape is not well established throughout the Keweenaw. However, small populations have been found in Calumet, Houghton near the Pilgrim River, and on the Tech Trails. Managing Oregon grape is similar to managing the more abundant Japanese barberry.

loosen soil with shovel
pulling by hand or with the aid of tools such as a shovel is the most effective strategy, as long as care is taken to remove as much of the root mass as possible
using a shovel to get under the main stem and leverage the plant out of the ground can help with hand pulling

Note: Oregon grape can easily resprout from roots left in the dirt, and their roots have a tendency to spread great distances underground. After pulling, the plant can then be hung in the forest or discarded as long as care is taken to keep the roots away from ground contact until the plant is dried out. If managing while the plant is actively fruiting, the seeds should carefully be bagged and discarded.

Native Alternatives

Species such as beaked hazelnut (Corylus cornuta) and downy arrowwood (Viburnum rafinesquianum) are native understory shrubs that inhabit similar areas, and would be great choices for replanting areas where Oregon grape has been removed. Beaked hazelnut has showy seeds that feed many native birds and rodents while downy arrow-wood produces purple drupes similar to Oregon grape that provide food for birds and small mammals alike.