Common buckthorn (Rhamnus carthartica) found popularity during the mid-1800s as a popular hedging and ornamental shrub, according to the Minnesota Department of Natural Resources. The Plant Conservation Alliance considers the buckthorn to be an ecological threat due to its invasive nature. Once established in an area, it is considered difficult to remove. Similar species include the Carolina buckthorn (Rhamnus caroliniana), lance-leaved buckthorn (Rhamnus lanceolata) and the glossy buckthorn (Rhamnus frangula).
The common buckthorn features a shrub growth form, reaching up to 25 feet in height with main stems reaching up to 10 inches in diameter. Curving twigs end with sharp, stout thorns. The gray to brown bark is similar in appearance to native plum and cherry trees. Once cut, the interior features yellow sapwood with orange heartwood.
The leaves of the buckthorn are egg-shaped with a pointed tip. Dark and glossy, the edges of the leaf are finely serrated. Three to five curved leaf veins appear on the top of each leaf. The fruit ripens in early fall to large, round clusters of 1/4 inch black berries.
Common buckthorn thrives in the understory of wooded areas. However, The University of Maine Cooperative Extension points out that buckthorn grows successfully in any conditions featuring ample light and exposed soil. Forming thick hedges and thickets, the buckthorn is most often found along woodland edges, pastures and roadsides. Growing well in a wide variety of soils, buckthorn is widespread from Nova Scotia to Saskatchewan, ranging south to Missouri and east to New England.
Each common buckthorn plant features either male or female flowers. Female shrubs feature fruits from May through June. In full sun areas, the buckthorn produces fruit at only a few years of age. However, in shady locations, the buckthorn fruit production may be delayed up to 20 years. The majority of the fruits fall directly underneath the mother shrub, contributing the thick growth of buckthorn. Birds and mice eat the berries, spreading seeds far from the parent plants.
The ability to thrive in sun and shade conditions combines with prolific fruiting creates an aggressively spreading shrub known to take destructively take over habitats. The quick growth competes with native plants for light, nutrients and moisture. According to the Wisconsin Department of Natural Resources the elimination of undergrowth on the forest floor leads to an increase of erosion in areas inhabited with buckthorn.
According to the Plant Conservation Alliance, methods of controlling common buckthorn include mechanical, physical and chemical methods. Prescribed burning helps to control buckthorn seedlings in fire-adapted areas during the late spring. Burning every year for 5 to 6 years helps to reduce the spread of buckthorn. Heavy buckthorn stands do not respond as well to fire treatment as the understory is well shaded and features little undergrowth.
Plants may be removed from the area by digging or pulling. Cutting large trees during the winter is effective when followed by an application of glyphosate herbicide.
The Minnesota Department of Natural Resources recommends regular follow-up in the area cleared of buckthorn, as the seeds remain viable in the soil up to 5 years.