The appearance of tree roots pushing up through a lawn is a common source of frustration for homeowners. These visible roots create tripping hazards, make mowing difficult, and compete with turfgrass for resources, leading to bare patches. Understanding the underlying reasons for this growth and applying targeted solutions can effectively mitigate the problem. The goal is to address existing surface roots while implementing strategies to prevent new ones from emerging, ensuring the tree’s health and stability remains a priority.
Why Tree Roots Seek the Lawn Surface
Tree roots primarily grow shallowly as a direct response to the availability of oxygen and water in the soil. The majority of a tree’s fine feeder roots, which are responsible for absorbing moisture and nutrients, reside in the top 4 to 15 inches of soil. This upper layer has the best gas exchange, providing the oxygen necessary for root respiration.
Compacted or heavy clay soils often exacerbate this issue by limiting the movement of oxygen into deeper soil layers. When the soil is dense, roots cannot penetrate easily and are forced to spread horizontally close to the surface where air is more readily available. Shallow and frequent lawn watering practices also encourage this growth pattern, as the roots have little incentive to grow downward in search of moisture.
Immediate Strategies for Managing Existing Surface Roots
For existing, exposed roots, homeowners must proceed cautiously to protect the tree’s stability and health. One of the safest and most effective immediate strategies is to change the landscaping around the tree’s base. Installing a layer of organic mulch or topsoil over the exposed roots can reduce trip hazards and protect the roots from damage by lawnmowers.
When using soil or mulch, it is important to apply only a shallow layer, typically a half-inch of topsoil, to cover the roots without suffocating them. Piling too much material, which is sometimes called “volcano mulching,” can reduce oxygen levels and harm the tree’s health. If a significant number of roots are exposed, replacing the turf with a mulched bed of shade-tolerant groundcover is often the most practical solution.
Root pruning should be considered a last resort and must be handled with caution, ideally by a certified arborist. Cutting large roots can severely compromise the tree’s structural stability and uptake of water and nutrients. Homeowners should avoid cutting any roots thicker than two inches in diameter and should never remove more than about 15% of the total surface root mass at once. Any necessary cuts should be made cleanly and as far away from the trunk as possible, preferably at a distance of at least three to five times the trunk’s diameter.
Modifying irrigation habits is a cultural solution that promotes deeper root growth. Watering deeply and infrequently encourages roots to seek moisture further down in the soil profile, rather than clustering near the surface. This technique involves applying enough water to soak the soil to a depth of six to eight inches, then allowing the top layers to dry out before watering again. This deep saturation manages the tree’s moisture needs while encouraging the grass to develop a more robust root system.
Long-Term Structural Solutions and Prevention
For long-term success, homeowners should consider structural interventions and proper tree selection to prevent future root encroachment. Vertical root barriers are physical barriers installed below ground to deflect root growth away from specific areas, such as a lawn, sidewalk, or foundation. These barriers, typically made of high-density polyethylene (HDPE, are placed in a trench to redirect roots downward.
The barrier must be installed to an adequate depth, generally at least 24 inches, to be effective at deflecting the roots. Barrier placement is important for the tree’s health, and it should not completely encircle the tree, as this can destabilize it. Instead, the barrier is placed strategically on the side where root growth is unwanted, such as along the edge of the lawn or path.
The initial choice of tree species is the most effective long-term preventative measure. Trees like willows, poplars, and silver maples are known for their aggressive, shallow, and expansive root systems, which make them poor choices for planting near lawns or structures. Conversely, selecting species known for developing deeper root systems, such as certain oaks, black gums, or ginkgoes, can greatly reduce the likelihood of future surface root problems.
In areas already experiencing severe surface root issues, converting the lawn immediately surrounding the tree to an alternative landscape is a permanent solution. Replacing the turf with a deep layer of mulch, or planting shade-tolerant groundcovers like hostas or ferns, eliminates the conflict between the tree roots and the lawn maintenance equipment. This change allows the tree to thrive without the stress of constant competition with the grass.