Tree roots anchor a tree and absorb water and nutrients. They consist of large, woody structural roots for stability and thin, fibrous feeder roots for nutrient uptake. Homeowners often need to cut roots when they conflict with infrastructure, such as sidewalks, driveways, foundations, or utility lines. While cutting roots resolves these conflicts, it risks the tree’s health and stability, requiring a cautious and informed approach.
Assessing the Risk to the Tree
Before cutting, evaluate the potential harm to the tree. Cutting large roots near the trunk severely compromises stability, increasing the risk of the tree falling during storms. Most of the tree’s sensitive root mass exists within a designated area called the Critical Root Zone (CRZ).
The CRZ is a circular area extending outward from the trunk, and a common arborist guideline defines its radius as 12 inches for every one inch of the tree’s Diameter at Breast Height (DBH). DBH is the measurement of the trunk’s diameter taken at 4.5 feet above the ground. Disturbing this zone significantly increases the chances of tree decline or failure, as it contains the roots necessary for survival and anchorage.
Small, thread-like feeder roots, typically located in the top 6 to 18 inches of soil, are generally safe to cut. Avoid large structural anchor roots that provide physical support. A practical rule suggests avoiding any root with a diameter greater than 10% of the tree’s trunk diameter. Cutting a root over four inches wide is strongly discouraged, as roots of that size are almost always structural.
Preparation and Locating the Roots
Root management begins with careful preparation and the precise location of the problematic roots. Gather necessary safety equipment, including gloves, eye protection, and sturdy boots, as you will be working with sharp tools and uneven ground. If the work is extensive or on public property, verify if local permits are required before starting.
To accurately identify which roots are causing the problem and to minimize unnecessary damage, the soil around the target area must be removed carefully. For shallow roots, simple hand tools like a trowel may be sufficient for initial exposure. For deeper or more extensive root identification, non-destructive excavation methods are preferred over traditional digging.
Specialized equipment like an air spade or a hydro excavator uses pressurized air or water to gently remove soil without harming the roots. Air excavation is ideal for loose soils and allows soil reuse as backfill. Hydro excavation uses a pressurized water stream to create a slurry, making it faster and more effective in dense or rocky soils. These methods fully expose the root to determine its size and direction before cutting.
Step-by-Step Guide to Cutting the Roots
Once the root is exposed and deemed safe to cut, the pruning requires precision and the right tools. Using a sharp tool is necessary because a clean cut promotes faster healing and minimizes entry points for pathogens. Appropriate tools include bypass pruners for roots under 1.5 inches, long-handled loppers for medium roots, or a specialized root saw for thicker roots.
The proper technique involves making a single, clean cut perpendicular to the root’s direction. Avoid tearing or crushing the root with dull tools, as this creates a jagged wound that is difficult to heal. Ideally, the cut should be made back to a lateral root or a healthy section growing away from the conflict area.
If the root is growing toward a structure, the cut should be made as far from the trunk as possible, preferably outside the CRZ. Immediately cover the exposed root end with soil or mulch. This covering protects the fresh wound from drying out and shields it from potential infection, allowing the tree to quickly seal off the surface.
Post-Cutting Care and Long-Term Root Management
After the cut, proper post-cutting care is necessary to promote recovery. The most important steps are ensuring the tree receives adequate water and applying a layer of mulch. Deep, infrequent watering encourages the regeneration of new, deep-growing roots.
Apply an organic mulch, such as wood chips, two to three inches deep over the root zone, keeping it several inches away from the trunk. This layer helps regulate soil temperature, conserves moisture, and protects remaining surface roots. Adequate moisture and mulching are crucial in the months following the cut while the tree regenerates lost root mass.
For a long-term solution, consider installing a root barrier to redirect root growth away from structures. Physical barriers, typically high-density polyethylene (HDPE), are installed vertically 30 to 48 inches deep to deflect roots downward. Chemical barriers use fabric impregnated with a slow-release herbicide to inhibit root tip growth, lasting between five and fifteen years.