The common buckthorn (Rhamnus cathartica) grows as a small tree or shrub. It usually only attains a height of 20 feet and the trunk rarely surpasses 10 inches in width. In the spring yellowish-green flowers appear in clusters of 2 to 6. The common buckthorn is either male or female. Black-colored, 1/4-inch-long fruit appears in clusters. Each fruit contains 3 to 4 seeds. The fruit offers wintertime food to birds but is poisonous to humans.
In the mid-1800s, European settlers brought the common buckthorn with them as an ornamental plant according to the University of Wisconsin. It quickly gained in popularity and was commonly planted as a hedgerow. Unfortunately, the common buckthorn became extremely invasive, and in the 1930s, the nursery industry in Minnesota ceased selling the tree as an ornamental.
The common buckthorn poses a serious threat to native plants. Its vigorous growth easily out competes native growth for valuable nutrients, water and sunlight. It is also a host tree that harbors crown rust fungus and soybean aphids which can prove damaging to native vegetation. The state of Minnesota has declared the sale or importation of the tree illegal in an effort to control its invasive habits but other states still legally sell and import the tree.
The common buckthorn has spread widely since the mid-1800s. Its distribution range runs from Nova Scotia all the way to Saskatchewan. It reaches as far south as Missouri and is widespread throughout most of New England according to Wisconsin Department of Natural Resources.
Seeds and Growth
The fruit of the common buckthorn is consumed by a wide array of birds. The seeds live through the bird's digestive tract acting as a mild laxative. They are widely dispersed wherever the bird goes. The common buckthorn seeds easily takes hold in light or shady conditions.
Prescribed burns biannually work well to control common buckthorn. Hand removal and pulling is rarely effective. Cutting the tree down offers no control, because the tree re-sprouts from the remaining trunk or root system. Herbicides such as 2,4-D with triclopyr and glyphosate offer excellent control when the directions for application are followed.