There are some small trees mixed in with the trees and shrubs along the back of my yard. Their leaves are staying green much longer than the other trees in my garden and I think they may be buckthorn. What is the best way to get rid of them if they are buckthorn?
— Leonarda Alvarez, Highwood
It is likely that you have common buckthorn in your garden. I also battle buckthorn in my home garden. The large buckthorns in my neighbor’s backyard mean that buckthorn removal is a constant annual maintenance task for me because each year my neighbor’s buckthorns drop seeds. Buckthorn is a shrub or small tree that can grow to more than 20 feet in height with a trunk of 10 inches or more in diameter. It is commonly found in home gardens in the Chicago area. It tends to hold green leaves late in the fall after other trees have turned color or fallen. Exotic buckthorns are invasive and tend to form dense thickets that crowd out other trees, shrubs and
wildflowers and seriously threaten natural areas. Many fruits fall below the plants, which creates a dense understory of seedlings. In addition, birds eat the fruits because there are few options other than buckthorn. This means a wider spread of seeds far from the parent plant. The buckthorn growing in your garden may be causing problems in natural areas near your home. Common buckthorns can grow almost anywhere. Buckthorn was introduced to North America as an ornamental shrub and selected because of its hardiness and ability to thrive in various soil and light conditions.
Common and glossy buckthorn readily take over and destroy natural communities. Common buckthorn takes over woodlands, savannas, and prairies. Glossy buckthorn takes over fen, bog and sedge meadow communities, as well as mesic upland sites, such as prairies. Dahurian buckthorn is mostly the same but not as widespread as the other exotic buckthorns. Three native buckthorns, Carolina buckthorn, alder buckthorn and lance-leaved buckthorn are found in Illinois and should not be removed from native areas. These, however, are very rare.
The best control measure depends on how big the buckthorns are and what plants might be affected by the removal. Smaller plants can be dug or pulled out, but the level of difficulty rises quickly with larger plants. Digging out large buckthorns may not be feasible if there are desirable trees or shrubs close by or if you have a lot of plants to remove. Buckthorn will readily resprout when cut back at ground level, so this is not a permanent solution. Cut stumps should be promptly treated with a stump killer after cutting with good results. Use a triclopyr herbicide (Garlon) or formulation of glyphosate (Roundup; or Rodeo for wetland areas) to treat the stumps. Brush-B-
Gone is a readily available retail product that has triclopyr as an ingredient. Treating stumps works in winter if you use proper techniques and herbicide. Be sure to follow label instructions when using any herbicide. This is a good time of year to cut your buckthorns down and treat the stumps with a stump killer. You can also try covering the stumps with black plastic that is anchored down to eventually choke off new growth. “Buckthorn Baggies” are a good option. If you choose this method, continue to monitor the stumps and cut back new growth that pushes up the plastic.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.