Submitted by Katie Zlonis, Botanist and Invasive Species Program Manager, Leech Lake Division of Resource Management
Common buckthorn (Rhamnus cathartica) is a highly invasive tree that, in less than a few decades, has rapidly taken over the understory of many forested areas in southern Minnesota, outcompeting native plants and destroying habitat for wildlife species.
It has been found in a handful of areas on the reservation, including in White Oak.
However, common buckthorn is capable of spreading and rapidly invading numerous habitats including upland forest understories, old fields, stream and lake edges, roadsides, and neighborhoods.
Because common buckthorn leaves stay green during late fall and early winter, those seasons are an ideal time to keep an eye out for this species and control or report it.
How can you identify common buckthorn?
Common buckthorn is a shrub or small tree up to 20-30’ tall. The bark is brown with silvery corky projections.
Buds and leaves are opposite, or nearly opposite each other on twigs (paired buds and leaves are nearly straight across from each other). Native cherry trees can have bark that appears similar to buckthorn, but cherries have leaves that are alternate along twigs (leaves and buds are not paired directly across from each other).
Common buckthorn twigs often end in a short, sharp thorn about ¼” long.
Leaves of common buckthorn are egg shaped, dark green, and glossy, with short rounded teeth and 3-5 distinct curved veins that extend from the mid-vein of the leaf to the edge. (see photo on right)
Plants produce round berries that eventually turn black when they ripen in late summer to early fall. The berries drop under the tree, eventually resulting in a dense understory of buckthorn seedlings. Birds also eat the berries, which aids in spread of this species to new areas. The berries are toxic to humans and animals, having a cathartic effect.
What can you do to help reduce or prevent the spread of buckthorn?
Early detection and control of this species is vital to keep it from spreading. Fall and early winter, when buckthorn is still holding onto its green leaves after other species’ have dropped, are the best times to locate plants. If you find common buckthorn on your property, there are several options for controlling it:
Pull: Small seedlings (less than ½” diameter) can be pulled directly from the soil. When pulling, try to minimize soil disturbance to prevent common buckthorn or other invasive species’ seeds from sprouting in the same area.
Cut and cover the stump: For larger plants, cut the stump near the base and cover it entirely with a tin can or black plastic bag that is fanned out from the base of the tree. You can nail the can to the stump, or if using plastic, stake it to the ground or tie a zip-tie around the bagged stump. The bag or can must be kept in place for at least one year. Buckthorn will resprout vigorously from a cut stump, and this method prevents those sprouts from surviving and reproducing.
If you find a large patch of common buckthorn that is impractical to control using the above techniques, please contact DRM (contact information below) and we will work with landowners to develop a strategy for controlling buckthorn on their property.
What should you do if you find common buckthorn?
If you think you have found common buckthorn on the reservation, please report this plant to the Division of Resource Management Plants Department 218-335-7442.
If you can provide specific information on location, that can help us identify and work to control new infestations as quickly as possible.