Lynda Ellis, Extension Master Gardener Intern in Anoka County.
Common buckthorn (Rhamnus cathartica) is a restricted noxious weed in Minnesota. It was brought to Minnesota as a hedge plant and decorative shrub. It escaped and is now found in nearly every Minnesota county, including Anoka.
What happens when buckthorn is planted? An impenetrable, messy thicket grows that out-competes native plants for nutrients, light and moisture; degrades wildlife habitat; and threatens the future of forests, wetlands, prairies and other natural habitats. It serves as a host to other pests, such as crown rust fungus and soybean aphid, and lacks natural controls that would curb its growth.
Do you have a woodlot or wild area on your property? Then you have or will have buckthorn. Do you live in the city or suburbs with no wild area? You are not exempt. Buckthorn planted many years ago is still around, possibly in your neighbor’s backyard. Birds eat its seeds and splat them around the neighborhood (note “cathartica” in the species name). Parks are not spared. For example, Locke County Park in south Anoka is infested.
How is buckthorn managed? Learn to recognize it. It can grow alongside other plants, such as lilacs or other trees, and hide for years. Look for green leaves late fall/early winter. Buckthorn will still be green after others are dormant. If there is a lot of it, it is a major undertaking to remove, and may need a professional. Saplings can be pulled by hand or with an extractor, and will not re-sprout. If they are not easy to pull, cut them off near the ground. Immediately paint the cut part remaining in the soil with concentrated Round Up (18% glyphosate), to prevent re-sprouting. Buckthorn can be cut and its stumps chemically treated during the growing season. Read the label and follow all instructions before using herbicides to control buckthorn.
Locke Park is being reclaimed. Truckloads of buckthorn were removed in 2013 and 2014. Much remains. A walk through part of Rice Creek Trail West (dashed red line on map, http://www.anokacounty.us/DocumentCenter/View/425) is instructive. Walking from west to east, you pass through a dense buckthorn thicket. This is a good place to practice your buckthorn tree and sapling identification skills. Continue walking and you emerge into reclaimed woodland. Look for small buckthorn there.
As the Locke Park reclamation people know, even if you removed the buckthorn on your property, your work is not over. Buckthorn seeds in the soil can remain viable for five years. Birds will deposit new seeds. Follow-up control of seedlings is important. With no follow-up, buckthorn will come back. Successfully banishing buckthorn requires a long-term commitment. For further information see: http://www.dnr.state.mn.us/invasives/terrestrialplants/woody/buckthorn/.