Trees & Shrubs
Helping Nebraskans enhance their lives through research-based education.
Tree Root Damage Can Be Serious
by Don Janssen, UNL Extension Educator
Do you have a sidewalk cracked or heaved out of place because of tree roots? Not only are the damaged sidewalks a potential accident for pedestrians, correcting the situation can be damaging to the tree. Prevention is the best possible way to avoid having to deal with problem tree root systems. When root problems develop, root pruning may be necessary. Root pruning, however, should not to be taken lightly.
Avoid planting trees in areas with less than three feet between paved areas. In areas with 3 to 4 feet between paved areas, plant trees that grow to a mature height of less than 30 feet. In areas with 5 to 6 feet between paved areas, select trees that mature about 50 feet tall. Reserve trees that mature higher than 50 feet for areas with at least eight feet between paved areas. This allows adequate space for the tree roots.
Consider installing expansion joints in the sidewalks near trees. This will limit possible sidewalk replacements to just a few sections rather than large areas. Building sidewalks on beds of coarse gravel is also effective at slowing or stopping the heaving. Tree roots will not grow through porous gravel; instead, they grow deeper.
Another method of forcing the roots deeper into the soil is to install a layer of expanded foam board (Styrofoam) under the cement. This treatment has the added benefit of allowing root expansion without pavement lifting. If roots grew between the concrete and the foam, their expansion crushed the foam without lifting the pavement.
Install root barriers along the tree-side edge of the sidewalk. The barrier will force tree roots to grow deep below the sidewalk, thus preventing heaving. Barriers can be made of plastic or geotextile fabric. It should extend one foot deep and at least 5 or 6 feet in both directions from the point on the sidewalk edge closest to the tree.
Whenever trees are root pruned, there is always some risk of tree failure. Many factors are involved. Tree species, age, size, site conditions, existing problems, vigor and extent of pruning are just some of the factors. Mature trees are less tolerant of root pruning than young trees, trees on sites exposed to high winds are less tolerant than sheltered trees, and trees with defects or poor general health are not good candidates for root pruning. The closer to the trunk the roots are pruned, the greater the effect on the tree. Make all cuts at least a distance of three times the trunk diameter from the outside of the trunk.
Tree root damage to sidewalks and other pavement is a serious problem. You can reduce this damage by installing treatments underneath or along side the pavement at the time of paving or at the time of tree installation.
University of Nebraska-Lincoln Extension in Lancaster County is your on-line yard and garden educational resource. The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office