The Chisago County Master Gardeners have answered many questions about controlling buckthorn over the years. Land that is not cultivated and left unattended is where buckthorn takes over. Once the shrub is established it is near impossible to eliminate.
This winter, more than one gardener has asked me if one can eliminate buckthorn during the winter. I also listen to the 8 a.m. Garden Show on Saturday mornings on WCCO radio. One of the hosts on the show is Julie Weisenhorn from the MN Extension Service. On at least three of the programs, someone has called in asking the question, “Can you control buckthorn during the winter”?
So I checked in with Donna Tatting, who also writes articles and helps me with some of mine. Donna did a lot of checking around and didn’t come up with definite answers; however, it does show there is interest in the subject.
Donna received information from Mary Meyer from MN Extension who wrote that she couldn’t recommend using a chemical for control of buckthorn, or any other plant when it is cold outside. I feel that below 50 degrees most chemicals don’t work. Mary continues by saying that tree stumps may take up the chemicals, but chances are the cold will be an issue as well as the snow.
Further digging by Donna Tatting came up with information from the Minnesota DNR that claims you can use chemicals during the fall and winter. They claim if you follow herbicide label instructions regarding temperatures, they can be applied during the winter. Water-soluble herbicides like glyphosate (Roundup, Rodeo, etc.) or triclopyr amine (Garlon 3A, Brush-B-Gone, etc.) can be applied to cut stumps when the temperature is above freezing. Oil-based products of triclopyr ester (Garlon 4, Pathfinder II) can be applied when temperature is below freezing.
To apply a chemical through the bark, use a low- volume spray application with Garlon 4 and similar oil-based products. This application uses triclopyr ester mixed with an oil diluent (Bark Oil Blue, kerosene, or diesel oil) applied directly to the bark of buckthorn from the root collar up about 12-18 inches. This treatment works best on stems less than 2-3 inches in diameter.
However, the best time to control buckthorn with chemicals is when the temperature is above 50 degrees. Whenever using any chemicals, always read and follow the instructions and precautions.
Our 16th Annual Spring Bonanza will be held Saturday, March 8, at North Branch Area High School. For more information and to register, call 651-277-0151 or visit z.umn.edu/chisagomgs.