September 1999, the Minnesota Department of Agriculture declared Rhamnus cathartica (European or common buckthorn) a restricted noxious weed. This means that sale, transportation, or movement of this plant is prohibited statewide by the Minnesota Department of Agriculture. Rhamnus frangula (glossy buckthorn) will join Rhamnus cathartica as a restricted noxious weed as of January 2001. Both species are considered invasive because they are capable of rapidly spreading and replacing native species throughout Minnesota. For help identifying buckthorn, see Yard & Garden Brief H402B, Common Buckthorn Identification.
European buckthorn was first brought to Minnesota from Europe in the mid-1800s as a very popular hedging material. Shortly after its introduction, it was found to be quite invasive in natural areas throughout Minnesota. The nursery industry stopped selling European buckthorn in the 1930's, but many buckthorn hedges may be found in older neighborhoods throughout Minnesota. Glossy buckthorn, also from Europe has been sold by the nursery trade in two different forms. Both forms reach a height of 12 feet. The cultivar 'Columnaris' has a narrow and tall form, while the cultivar 'Aspenifolia' spreads up to 10 feet and has narrow leaves that give it a ferny texture.
European buckthorn is the most problematic species of buckthorn because it is both drought and shade tolerant. These characteristics enable it to become invasive in woodland understories or at the edges of prairies or fields. In more recent years, glossy buckthorn has also been shown to be an invasive plant, problematic mainly in wetlands and moist woodlands. Both types of buckthorn have berry clusters that attract birds who then deposit the seeds in their droppings. This process allows for large quantities of buckthorn to become distributed over vast and diverse areas.
Both mechanical and chemical treatments may be implemented to remove buckthorn. While buckthorn does not re-sprout from underground roots, it can re-sprout from the buds at the base of stems if they are not cut close enough to the ground. It can be difficult to determine how close to the ground the cut should be made; using one of the herbicide treatments recommended below will prevent these buds from re-sprouting.
For buckthorn stands containing individual plants 3/8 inch in diameter or less, hand pulling may be the most effective method of removal. Uprooting the small plants can be aided by using a weed wrench or shovel to help loosen their roots. This is a practical method for small stands of buckthorn, but may not be practical for large stands due to the amount of labor involved. Buckthorn plants that are greater than 3/8 inch in diameter may be more difficult to pull out of the ground. To loosen their roots, soak the soil around the trunk for several days before pulling. Before you pull or dig buckthorn out of your soil, call Gopher State One to ensure there are no buried utilities in the area.
When controlling large quantities of buckthorn, cutting the stems, then painting or spraying the stumps with the herbicide glyphosate (commonly sold as RoundUp) is quite effective. You will need to buy a concentrated form containing 25 percent or higher amounts of the active ingredient, glyphosate. Stores may carry concentrated forms containing smaller percentages, so it is important to read the fine print on the label. Farm and landscape supply stores often sell this more highly concentrated glyphosate.
The proper time to cut buckthorn and apply glyphosate is when the plant is active or when the leaves are fully expanded and temperatures are above 32° F. This will ensure that the herbicide is taken up by the plant. The herbicide must be applied within 24 hours of cutting, but applying it immediately after cutting is best. In cases where more than a few plants are treated, it is beneficial to add a dye to the herbicide to mark cut stumps and bark you've already sprayed. Laundry blueing works well, is inexpensive, and is available at the grocery store. If you choose to use an herbicide as a means of buckthorn control, always read and follow label directions to prevent danger to yourself (the applicator), and to the environment, and to ensure that the herbicide will work effectively.
When feasible, removal of buckthorn in the landscape is encouraged. When it is not feasible to remove buckthorn, such as the case for some homeowners with large mature hedges, one last option may be used to prevent the spread of buckthorn without removing the plants. Pruning or shearing frequently (at intervals of every 3-4 weeks) can dramatically reduce or eliminate the flowers and subsequent berries. This method is effective in preventing birds from eating the berries and distributing buckthorn seeds only if it is done frequently as suggested above.
Yard & Garden Line News, Controlling Buckthorn April 1, 2003
Pest Alert Factsheet Buckthorn and its Control. 1995. Minnesota Department of Agriculture.
Buckthorn Minnesota Dept. of Natural Resources.
Common Buckthorn Identification Minnesota Dept. of Natural Resources.