Problems with tree roots fall into two main categories. Either the roots themselves have a problem such as girdling, rotting, lack of moisture, or a pest or disease that leads to the decline of the tree, or the roots cause problems in their surroundings.
Common Problems Caused by Tree Roots
To understand the impact that tree roots can have, it is important to keep in mind that the roots of a tree spread two to three times as wide as the radius of the canopy. In dry conditions, they can spread even as much as five times as wide. For example, a tree with a canopy of 12 feet—which equals a radius of six feet—the roots can spread 18 to 30 feet from the trunk.
Also, most roots are nearest to what they need to survive—water, oxygen, and nutrients—and that is naturally near the surface. That’s why most tree roots are located in the upper 18 to 24 inches of the soil.
Damage to Underground Pipes
While tree roots can break pipes, the more common occurrence is that pipes break on their own because of age or other physical weakness, and then the tree roots grow into the pipes and lead to pipe blockages. Sewer pipes are especially susceptible to that type of problem. The trees that cause the most sewer line damage are aspens, birches, elms, maples, poplars, swamp oaks, sycamores, willows, and fig trees.
To prevent this from happening, practice sewer-safe landscaping:
- Know where the pipes are located on your property and avoid planting anywhere near them. Plant trees as far away from the pipes as possible.
- Choose trees that to cause fewer problems, such as amur maples, Japanese maples, flowering dogwoods, or crabapples.
Damage to Pavement and Sidewalks
Tree roots can grow close to and underneath pavements and sidewalks. If the roots are near the surface, they can lift the pavement, which not only causes damage but also creates a tripping hazard. When that happens, the choice is often between saving the tree by moving the pavement farther away from the tree roots or severing the encroaching roots of the tree and taking the risk of killing the tree to save the pavement or walkway.
Ways to prevent this include:
- Plant smaller trees and keep a minimum distance of four feet between the tree and the pavement. A rule of thumb is to plant trees with a mature height of less than 30 feet at least five feet away from the sidewalk, and trees with a mature height of 50 feet not closer than five to six feet from a pavement. Stay away from any trees that exceed that size.
- Install mechanical barriers along the tree-side of the pavement to prevent roots from growing underneath. The barriers, which can be made of plastic or geotextile fabric, force the roots to grow deep in the soil, so they won’t be able to lift the pavement. Place the barrier one foot deep in the soil and draw an imaginary line from the tree trunk to the sidewalk, then place the barrier five to six feet along the sidewalk in either direction.
Surface Roots as Hazards
If you have a maple tree growing in your backyard, its big, strong roots protruding from the surface might be a familiar sight. This often occurs on a slope where soil erosion leads to root exposure. And after a winter with warm spells, it can get worse, as the freezing and thawing cycle causes frost-heaving.
Not only are these surface roots unsightly, they are also hazardous. And they can be a real headache when you are mowing the lawn. Because they are so exposed, the roots are also prone to injury.
Instead of severing the roots, mulch the area under the tree with hardwood mulch or well-matured loose compost. Note that you should not cover the roots with more soil. Adding more soil starve the tree of water, air, and nutrients. Raising the ground level by adding soil is almost never advisable.
Mulching has several benefits. Mulch lets plenty of oxygen through and at the same time insulates the soil, so it reduces the effect of frost-heaving. Replacing the grass with mulch makes mowing unnecessary and the tree and the lawn won’t compete for water and nutrients any longer.
Do Tree Roots Damage Foundations?
Not necessarily. Trees that are planted too close to a foundation can lead to multiple problems, but not always because of the roots. The soil around a foundation is usually very dry, especially if the area is covered by a roof overhang. Meanwhile, tree roots grow towards moisture, so they will usually expand in the opposite direction away from the foundation.
If there are cracks in the foundation that were caused by other circumstances, such as soil pressure or shrinking, smaller tree roots might penetrate those cracks, but they usually won’t create more structural damage than what’s already there.
Any problems caused by tree roots should not deter you from planting trees even if your yard is small.