Common buckthorn (Rhamnus cathartica), the perfect invasive plant.

Common buckthorn flowers. Photo by Peter Dziuk.

Typical leaves of common buckthorn.

Buckthorn twigs showing the classic thorn. Photo by Leslie Mehrhoff.

By Joseph Mooney
Invasive plant of the week returns! This week’s invasive plant is common buckthorn (Rhamnus cathartica).
If you’re looking for the poster child of invasive plants, common buckthorn would be at the top of the list. This aggressively spreading woody plant is native to Europe and western Asia. It was introduced to the United States as an ornamental in the early 1800s.
Walk through just about any park or neighborhood in Ann Arbor or southern Michigan (and many other states) and you’ll see thickets of buckthorn taking over landscapes, home gardens, and fence rows. Sometimes it forms an impenetrable wall of vegetation. Unsuspecting homeowners even unwittingly nurture single specimens as if they were worthy horticultural plantings. Of common buckthorn’s landscape-altering qualities, writes, “It is discouraging that there is now an entire generation of young adults for whom a relatively open and diverse woodland is unfamiliar.”

An example of buckthorn’s bark (which is not worse than its bite!).

Buckthorn fruit is easy to recognize with its round shape and deep-purple, nearly black color.

Buckthorn distribution map. University of Georgia Center for Invasive Species and Ecosystem Health. 

A growing and reproducing machine, common buckthorn is, so to speak, a nearly perfect invasive plant. It tolerates a wide variety of environmental conditions, including shade and wet or dry sites. It grows quickly. It forms dense stands that crowd out everything else, including native plants. It produces copious berries that are eaten by birds and other animals that then spread the seed to the four corners. There is even evidence showing that common buckthorn is allelopathic—producing chemicals that inhibit the growth of other plants. It’s a doomsday invasive plant.
Once you see common buckthorn you won’t forget what it looks like. There are plenty of clues. The leaves stay green and persist into late fall and even early winter. In the spring common buckthorn leafs out early. In summer and fall clusters of dark-purple or nearly black berries cover the branches. Twigs may have a thorn at the tip. Inner bark is orange.
Effective control includes removal of fruit-producing plants, mechanical pulling of seedlings, and, often, targeted application of herbicide to the cut surfaces of stumps. These processes will likely need to be repeated multiple times.