Buckthorn is the most persistent of the invasive species of tree in our area. In some places it can provide screening from neighboring houses, but it can also be quite harmful.
It’s good to know that fall is the ideal time to spot where all of them are on your property. Once the leaves have just fallen off most of the other trees, those on buckthorns remain green. So now is a good time to mark those trees that should be removed.
In particular, the buckthorn that you specifically should remove are those clustered around any established tree, such as an oak, that you want to keep. For reasons that are unclear, the very deep-rooted buckthorns will eventually kill the larger tree. When a buckthorn grows to about a foot in height it is almost impossible to pull it out by hand because of its deep and spread-out root system.
Removal requires either digging out the smaller ones or cutting larger ones off at ground level. The stumps must then be “painted” with a concentrated weed killer. That weed killer gets sucked down into the roots and kills the plant without damaging others nearby. If you don’t do this final step the buckthorn will grow right back. But be careful! Thorns on a larger buckthorn are sharp, often over an inch in length and strong enough to puncture a garden tractor tire or shoe sole. Ouch!