Tree roots sometimes require cutting to maintain the landscape, complete necessary repairs, or mitigate damage to built structures. Successful root removal without killing the tree depends entirely on the cut’s location, the root’s size, and the method employed. A strategic approach is necessary because the root system anchors the tree and absorbs water and nutrients. Understanding the proper technique for each scenario determines the tree’s long-term health and stability.
Techniques for Pruning Roots in the Landscape
Pruning roots in a landscape setting is often done to prepare a tree for transplanting or to manage its size. This process must be highly controlled to ensure the tree remains stable and healthy. For mature trees, experts suggest avoiding cuts closer than a distance equal to three to five times the tree’s diameter at breast height (DBH) to protect structural roots.
Clean, sharp tools are required to create a smooth surface that encourages proper healing and limits disease entry. Use a sharp spade, bypass pruners, or a root saw, rather than tearing roots with heavy equipment like an excavator. After the cut is made, the area should be backfilled with soil and kept moist to reduce stress on the remaining roots. The ideal time for this pruning is typically in late winter or early spring when the tree is dormant.
Removing Surface Roots Near Structures and Hardscapes
Roots near sidewalks, driveways, or foundations often require removal because they can lift and crack concrete, creating tripping hazards and structural damage. The greatest damage tends to occur within six feet of the trunk, where roots are thickest and most actively growing. When cutting intrusive roots, avoid severing any root greater than two inches in diameter, as these are often structural and compromise stability.
For thick, woody roots, use a sharp lopper or a reciprocating saw with a specialized blade to make a clean cut, which is preferable to a ragged tear. Immediately after cutting, install a physical root barrier vertically in the trench to redirect future growth away from the structure. These barriers, made of durable plastic or metal, should extend 24 to 36 inches deep, as most invasive roots grow near the surface. Chemical root inhibitors, such as fabrics containing trifluralin, can also be installed to temporarily prevent root growth.
Specialized Methods for Clearing Roots from Plumbing
Root intrusion into underground sewer and drainage pipes requires specialized techniques because the roots grow inside the pipe system. Tree roots are attracted to the moisture and nutrients leaking from pipe joints or small cracks. Once inside, they expand and trap debris, leading to significant blockages. The most effective mechanical method for removing these blockages is hydro-jetting, which employs high-pressure water streams (3,000 to 8,000 PSI).
The specialized nozzle used in hydro-jetting features forward-facing jets to break through the root mass and rear-facing jets that scour the pipe walls clean. This process completely removes the root mass and small root hairs, significantly delaying regrowth compared to traditional augering. Chemical methods offer a complementary approach, involving foaming root killers designed to destroy the roots within the pipe. These chemicals are flushed through the system to prevent future growth by killing the root tissue.
Copper sulfate is another chemical agent sometimes used, acting as a root repellent, though its use requires careful environmental consideration. While chemical treatments are effective for maintenance, hydro-jetting or professional root-cutting augers are necessary for severe, active blockages. It is safest to consult a licensed plumber for proper diagnosis using a sewer camera before attempting any clearing method.
Assessing Tree Health and Minimizing Damage
Any time a root is severed, the tree experiences a loss of its ability to absorb water and nutrients, placing it under stress. To minimize this effect, arborists define a Critical Root Zone (CRZ), which represents the minimum area of roots required for health and stability. For a non-specimen tree, the CRZ radius is calculated as one to one-and-a-half feet for every inch of the tree’s DBH.
Most of a tree’s root system is concentrated in the top 18 to 24 inches of soil; structural roots are often located closer to the trunk. Severing a large percentage of the root mass can lead to canopy dieback, instability, or death, particularly if major structural roots are cut. Healthy trees can tolerate the removal of up to 25 to 30% of their total root mass, but exceeding this threshold significantly increases the risk of decline and structural failure.
If construction or pruning must occur near the CRZ, tunneling or boring under the roots at least 18 inches deep is the preferred method to prevent severe root loss. After any root cutting, monitor the tree for signs of stress, such as thinning foliage or wilting. Providing supplemental water and mulch will help the tree recover.