Ask Mr. Smarty Plants

Populus tremuloides (quaking aspen) Quaking aspen reproduces rapidly from seed and root suckers. It is short-lived and plagued by disease and insect problems, but is practically indifferent to soil conditions. From the USDA Forest Service website Populus tremuloides you will get a lot of technical information on how and why this plant suckers, but not much suggestion in how to limit it. 

Rhus glabra (smooth sumac) is the only plant native to all 48 contiguous state. Sumacs will grow in dry waste areas, such as impossible slopes where even junipers struggle. They are fast growing, generally pest and disease-free, and drought-tolerant. Colonies are often single-sexed, formed from a single, suckering parent. Only female plants produce flowers and berries.

Ordinarily, when we are asked about control of suckering, it has to do with a tree or plant that has been cut down, and the gardener is trying to eliminate. The suckering, besides propagating the plant, is also a defense mechanism against damage, such as being cut down. In those cases, we recommend cutting off or pulling the suckers immediately when they reappear. For saplings already established from the parent root, the best way is to cut them off close to the ground and paint the cut surface within five minutes with a broad-spectrum herbicide. This gives the herbicide access to the roots befoe the cut begins to heal over to protect itself. However, in your case, you probably don't want to do that as you apparently wish to keep the parent trees.

We found a couple of articles about installation of root barriers, but these had to do with protecting foundations from encroaching tree roots. The first is from Horticulture Update from the Texas A&M University Cooperative Extension, Root Barriers. Another article, Root Barriers Prevent Costly Damage offers some more possibilities.

We have no personal experience with these procedures, but hope you can develop your own way of dealing with those roots.

Populus tremuloides

Populus tremuloides

Rhus glabra

Rhus glabra