Root problems: girdling roots, compaction, deep planting and grade change

This page reports what the named codes, regulators and makers say. It is not training and does not teach the work. The publications are extension fact sheets and articles, not standards or law. Rules for protecting roots on building sites, such as protection zones, are on the trees and construction guide. The planting side, including the flare, is on the planting depth page. The courses that teach tree work are on the certifications guide.

Girdling roots

University of Maryland Extension (page updated April 19, 2024) defines a girdling root as one that grows in a circle or spiral around the trunk, at or below the soil line, gradually strangling it. It says circling roots can slow and eventually cut off sap flow so that sugars made in the leaves cannot reach the roots. It says they may form in root-bound container plants, begin at transplanting, or develop as a tree grows, and that poor planting, deep mulch or compacted soil seem to encourage them. It lists red and sugar maples, 'Greenspire' lindens, American beech, pines, oaks, poplars, zelkovas and elms as the trees that most often develop them, and says affected trees tend to decline over 5 to 10 years.

The symptoms it lists are a thin crown with stunted growth, lighter green or scorched leaves with early fall colour and leaf drop, dieback, and a straight trunk side with no natural flare, which digging may show to cover a girdling root. Severe cases may lean or break off.

On treatment, the Maryland page says small girdling roots can be removed with a sharp chisel and mallet, taking out several inches of the root where it meets the trunk so that it does not reconnect. It says that if a large root has grafted with the trunk it is advisable to leave it, that cutting a V-shaped notch in the top half of the root may help weaken it, and that removing roots over 2 inches in diameter is more involved and a licensed arborist is best consulted. Penn State Extension (article updated September 28, 2026) gives a similar line from an urban forestry educator: a root under 2 inches in diameter can be cut, one over 2 inches calls for a certified arborist to judge whether it can safely be cut because a larger root may have become structurally important. The author describes cutting a 3 inch root on a sycamore with a hand saw after removing the soil around it, and says the tree needed monitoring afterwards for crown dieback.

Penn State's article on container-grown trees (updated August 25, 2025) says roots in a pot hit the sides and turn, and that several years after planting the circling roots begin to girdle the stem and can kill the plant. It says research shows it is best to sever roots with a sharp knife, handsaw or spade, and that shaving the sides of the root mass works. It names air-pruning containers and a copper-treated container coating as nursery measures against circling roots.

Soil compaction

The Maryland page on compacted soil (updated February 28, 2023) says compaction forces soil particles closer together and reduces the pore space that air and water move through, so fine feeder roots struggle to expand. It names heavy foot traffic, working or walking on wet soil, construction equipment and vehicles parked under trees as causes, calls it a major problem after construction, and says clay soils compact more than sandy ones. Symptoms it lists are wilt, scorch, early fall colour and dieback, usually progressing over years.

It says prevention is the way to avoid compaction: fencing around trees on building sites, defined paths, double overlapping plywood sheets where heavy equipment is unavoidable, and a 3 inch layer of organic mulch over roots. It says correction is difficult, that working organic matter into the soil is not recommended around existing trees, and that arborists sometimes use an air spade to fracture compacted soil without removing it, working in small pie slices under the crown and backfilling with native soil and organic matter.

Planting too deep

The Maryland page on deep planting (updated November 16, 2023) says a depth only one inch too deep can cause trouble and that trees are often found three or more inches too deep with mulch on top. It says deep planting causes bark deterioration at the soil line, takes a few seasons to kill a plant, and shows as new growth each spring that dies back in summer, then cankers and deep bark cracking. It says a trunk that has no visible flare invites suspicion of deep planting or girdling roots. For a tree planted too deeply and not long in the ground it says the tree can be lifted and replanted, and for an established one that root collar excavation, removing excess soil and mulch down to where the trunk flares, can sometimes help, done by arborists with an air spade and recommended for valuable or specimen trees.

Grade change

The Maryland page on grade changes (updated February 28, 2023) says any addition or subtraction from the natural soil grade adversely affects trees and shrubs, with old established trees the most sensitive. It sorts species into three groups: sugar maple, beech, dogwood, oak, tulip tree, pines and spruce as very sensitive; birch, hickory and hemlock as less sensitive; and elm, poplar, willow, planetree, pin oak and locust as least sensitive. It says fill over roots hampers gas exchange, that excess soil against the trunk raises the decay of lower bark, that clay does the most injury with fill of more than an inch, and that lowering grade can be as serious because it removes feeder roots, most of which it places in the top six inches of soil, while most tree roots lie within the top three feet. The page names tree wells and perforated pipe systems as preventive measures and gives three inches of soil, less if the soil is high in clay, as the maximum that can safely be added without special provisions. It adds that when distress is severe it is usually too late, even after the fill is removed.