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Common buckthorn has become a threat to Minnesota’s woodlands, prairies, abandoned fields and roadsides because it is capable of growing in full sun and dense shade and it is adaptable to adverse habitats. Buckthorn will rapidly form dense thickets and push out native species if left untreated. Its primary means of spreading, by seeds that are eaten by birds during the winter months, makes it all the more difficult to control. Although three buckthorn species can be found growing in Minnesota, common or European buckthorn (Rhammus cathartica) is the most problematic.
Characteristics
Common buckthorn is a multi-stem shrub to a small tree, growing 10 to 15 feet tall with an upright oval form. The leaves are egg-shaped with finely toothed edges, very dark, and dull to glossy green. They leaf out in early spring and retain their leaves well into winter. This quality makes them easiest to identify in late fall when native shrubs and trees have lost their leaves. Buckthorn leaves do not change color before being shed. The tops of the twigs provide a readily identifiable characteristic, with a sharp thorn at the tip of the twig. The bark is very rough grey/brown, similar in appearance to cherry and plum trees. The common buckthorn has berry-like three-eighth inch glossy black fruits borne in clusters, which are retained well into winter. Each fruit has three to four seeds.
Control
The best method for controlling buckthorn depends upon the size or density of the plants to be controlled. Buckthorn seedlings can be pulled by hand if the stem is under one-half inch in diameter. Removal is easiest when the soil is moist. Larger plants, one to one-and one-half inches in diameter, can be dug or pulled using a type of mechanical device (available at most rental stores). Larger plants are harder to remove by hand, and should be cut at the base. Because buckthorn can easily re-sprout from the cut stump, additional action must be taken. If only cutting a few stumps, they can be covered with a tin can or black plastic to prevent re-sprouting. Otherwise, stumps should be treated immediately after cutting using an herbicide containing glyphosate or triclopyr.
If the amount of buckthorn plants to be removed would prohibit working with individual plants, a foliar spray of herbicides is also effective, keeping in mind that overspray can kill or damage non-target vegetation. Follow-up treatments may be necessary for several years if plants re-sprout. Always read and follow all label instructions for the safest and most effective use.
In general, the best time to treat buckthorn with an herbicide is late fall. At that time the sap is flowing towards the roots allowing for maximum herbicide absorption. In addition, since buckthorn retains its leaves later into the fall than most other plants, they are easily recognized. Fall applications are also less likely to be damaging to non-target plants.
Good luck in buckthorn busting! - Dick Dostal, Master Gardener
Credit: University of Wisconsin PUB-FR-216 2002