Aspen trees (Populus tremuloides), also known as quaking aspens for their leaves that tremble on flexible leaf stalks in the breeze, produce spectacular fall foliage in U.S. Department of Agriculture plant hardiness zones 1 through 7. In addition to adding beauty to landscapes, the aspen serves as a succession tree. With its seeds and underground suckers, it quickly fills in areas where vegetation was lost, such as to fire, and thus it helps prevent erosion in many wild areas. In the home landscape, however, rapidly spreading roots are more often troublesome than helpful. Stopping aspen roots from spreading into your garden, lawn or other areas it shouldn't, requires diligent care and clever landscaping.
Aspen shoots appear from both the trunk and roots as a form of vegetative reproduction. Trees anchor and spread quickly with this particular adaptation. One strategy to prevent root spread uses barriers. Commonly constructed of plastic or metal, thick sheets are installed vertically in the ground along the tree's perimeter, such as between the aspen and your garden. Because aspens have shallow roots that go down only about 12 inches deep, a barrier approximately 24 inches deep should keep the majority of roots from sprouting new shoots in your garden.
Aspen roots are notorious for appearing in lawns, much like small weed sprouts. Before they grow longer and thicker, mow your lawn as usual to cut the roots off. Use your lawnmower's bagger to store and discard the root pieces away from your lawn and garden. Maintain sharp mower blades to quickly cut through the roots, as well as your long grass. This strategy works well during your lawn's active growing period, depending on the species. Spring, summer and fall often require mowing at least once a week which keeps these overzealous aspen roots under control.
Growing up to 50 feet tall with a 25 foot spread, Aspen trees produce root systems that grow well past their drip lines in search of nutrients, oxygen and moisture. As a result, your nearby garden may have small sprouts emerging from the soil. Diligently prune these growths away with garden shears before they grow too large to cut by hand. Be sure to first disinfect the shears before pruning, as with any plant. A household disinfect will work, or you can make a solution, such as by mixing one part water and nine parts chlorine bleach. Discard the suckers far away from your garden. Any pieces that fall to the ground can potentially root and propagate the tree in an undesired location.
Deep Watering and Pruning
Aspens use their spreading roots as a self-preservation tactic, especially when under stress. To prevent stress, maintain a healthy tree with a deep root system by allowing the soil to dry between irrigation sessions. When you do water, however, thoroughly saturate the entire root system to force the roots downward for moisture absorption. Aspens that are not severely pruned or disturbed at root level through cultivation have less sprouts emerging from the ground. They do not waste energy on vegetative spread if the mother plant is healthy. Spread mulch around your Aspen as well to conserve soil moisture as roots remain deep within the ground.