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Larry Sagers Horticultural Specialist Utah State University Extension Service Thanksgiving Point Office © All Rights Reserved
Aspens are notorious invaders of lawns. In natural areas this helps the trees spread into areas that have burned or have no trees growing on the site. In lawns and flower beds it can be a frustration to have small trees emerging throughout the year and taking over the garden. Aspens sprout more readily in warm, exposed soils. Injuries to the roots by mowers or cultivators will increase problems.
Aspen sprouts can usually be confined in beds if surrounded by impermeable material that extends 12" into the soil. Use barrier materials that will not decompose including concrete, pressure treated lumber, heavy plastic, fiberglass or steel. The barrier must be several feet from the trunk of the tree. Groundcovers and shrubs that are not disturbed can also reduce sprouting.
Tree shoots or sprouts grow from the underground stems called rhizomes that spread from many larger trees or shrubs. These may grow several inches to many feet from the base of the parent tree. These sprouts are different from the shoots that grow from the base or trunk of the tree; these sprouts are called "suckers", and they are weak structures that should be removed as they appear. They will not grow into strong branches nor strong new trunks. They will only drain energy from the parent plant.
Root shoots, on the other hand, can grow into strong, healthy replacement trees. This is good and bad. It is good in the case of short lived trees or trees that are prone to insect and disease problems, such as aspen it is easy to replace the plant. If the parent tree dies, the root shoots provide a free replacement. If you want more trees in your yard, simply grow them from the shoots. Remember the replacements are susceptible to the same problems.
If you don't want more trees, the root shoots become weeds in the lawn. There are no good ways to prevent the growth of these root sprouts other than using barriers. There are not even any good ways to get rid of them. If they are a severe problem consider replacing the tree or shrub with a variety that does not have the problem.
Some herbicides will kill shoots, but the shoots must be severed from the main tree before they are treated. Otherwise the herbicide can sometimes travel through the root and into the parent tree, causing permanent damage or even death. Glyphosate (or Roundup as it is commonly known), and 2,4 D are translocated herbicides that will travel varying distances back to the main trunk.