Green Thumb
Posts: 480
Joined: Sat May 16, 2009 2:52 am
Location: Crystal, MN (Zone 4)

The Buckthorn Predicament

I'm having a bit of a problem figuring out to do with some large buckthorn trees in my yard. They're growing amidst some nice lilac bushes and I don't want to damage them removing the buckthorn. From what I've read the only way to get rid of buckthorn is to either chop/dig out the stump or poison the stumps with roundup. Digging/chopping out the stumps doesn't seem to be an option because I don't want to damage the lilac roots, and I'm afraid poisoning the stumps might poison the lilacs as well. Am I in danger of poisoning the lilacs as well (some are inches away)? Or is it safe to poison them? If not what else can I do to stop this nuisance of a plant?

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Location: Oregon

I can't say for sure, but I had a filbert (hazelnut) tree growing smack up through the middle of one of my favorite big rhododendrons. I cut it down twice, and it just kept coming back. I finally talked to the people at a good local nursery, and they told me I had to cut it down again, spray the stump with brush killer, wrap it in black plastic and cover the whole business with an upturned bucket or half-barrel. (They said if it got any light, it would resprout.) I did that a few weeks ago, and the rhody is just starting to bloom. The leaves aren't showing any evidence of being damaged by the brush killer. I was very careful, of course, not to get any of the brush killer on the rhody's trunk, branches, or leaves. In fact, I painted it on the stump of the filbert, so there wouldn't be any chance of spray drift.

Green Thumb
Posts: 439
Joined: Thu Nov 09, 2006 4:17 pm
Location: Midcoast Maine, Zone 5b

Depending on how large your lilacs are you might have the option of lifting them (lilacs tend to be "easy movers" with relatively shallow root systems) removing the buckthorn and replanting. It is, however, getting a bit late for this project in Minnesota (ideally I'd aim for as early as you can get a shovel into the ground).
I have used the cut and paint the stump method (using a 50% concentration glyphosate) with success but not with these two exact species. As long as the species are dissimilar there should be little or no chance of root grafts that could translocate the herbicide to the desirable species but I still approach these projects with trepidation. Do not use a spray! Paint the herbicide on the cut(s) (I use disposable foam brushes) immediately after making it/them and do it on a still day with temps in the 70sF. Too warm (85+) or too cool (less than the upper 60s) and it will be much less effective. I have had the best success using this method in late summer or early fall.

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