Dealing with late aspen root suckers

New aspen growth years after the original trees
have been eliminated

Even years after an aspen clone has been eradicated by girdling, scattered root suckers may appear. For instance: the big aspen clones at Black Earth Rettenmund Prairie were eliminated in 1986-1987, yet in 2012 we had quite a few new shoots. There isn't any seed bank, so these shoots have presumably arisen from underground rhizomes that have reawakened after many years of dormancy. You can't really ignore them, as they have the potential to turn into aspen trees. But the technique for getting rid of them is different than what you use on the trees.

Fortunately, these suckers are very sensitive to herbicide, and basal bark with Garlon 4 in oil works magic. The paint stick works very well, and a swipe at the bottom of each stem will kill it. An alternate is to spray about a 4-6 inch strip up the base of each stem, using a hand spray bottle. Either method is quite economical of herbicide and damage to nearby good plants should not occur. (I killed two aspen stems with no visible effect on a flowering wood lily plant that was less than a foot away!) I don't recommend using a backpack sprayer instead of a hand spray bottle, as it uses a lot more herbicide and can potentially cause peripheral damage.


Early June is a good time to canvas an area for aspen suckers, because they are easy to find. The photo below shows a fairly typical patch of aspen that it took about 10 minutes to treat.

Small aspen plants that were treated abut 2 weeks before with Garlon 4 basal bark.

The herbicide mixture we use is 20% Garlon 4 (one part Garlon 4 and four parts bark oil). You can purchase Garlon 4 at almost any agricultural co-op, and the co-op should also be able to supply a suitable oil.