Girdling Roots
Click for larger image Girdling root on Japanese tree lilac (Syringa reticulata); also planted too deep

A tree is girdled when something is tightly wrapped around the trunk or stem. A stem girdling root circles or partially circles the base of a tree at or just below the soil surface.

Stem girdling roots choke off the flow of water and nutrients between the roots and branches and food produced in the leaves from reaching the roots. They can also compress and weaken the trunk of a tree at or above the root collar flare (the junction between the trunk and the main roots) causing it to lean and lose its stability. Girdling roots may girdle other roots, but there is no known harm in this. Trees having stem girdling roots suffer a slow decline in health and a premature death.

The appearance of a tree trunk will be affected by a girdling root. Usually tree trunks flare out where they enter the ground. The root will prevent the collar flare, sometimes the trunk may get narrower and appear flattened or sunken. The threat depends on the size of the root and the amount of the tree’s circumference affected. It is almost impossible to predict if a developing girdling root will cause problems for a tree. However, if a tree has girdling roots it is more likely to have problems than one without them.

The causal factors may be genetic or cultural. At the end of this article is a list of trees that may be more prone to stem girdling roots. Cultural practices that may cause girdling include poor growing practices or poor planting techniques.

Most tree roots are in the top 6 to 24 inches of soil and grow out from the trunk in a spreading manner. Cultural practices that can adversely affect this natural root pattern include: (1) Planting in a hole that is too small so the roots can not easily spread out. (2) Planting container grown trees that have roots growing in a circular pattern. (3) Planting a bare root tree by twisting roots to fit into a small hole. (4) Leaving wire baskets, burlap and any part of a container in the planting hole. (5) Piling mulch against the trunk of a tree (creating a mulch volcano).

The most common theory of the cause of stem girdling roots, is that they develop as a result of trees being planted too deeply. When root systems are buried, less oxygen and water is available. The roots will grow up towards the surface of the soil and tend to encircle the trunk. The more deeply buried the roots are, the fewer the roots available for the tree to become established.

Symptoms and Diagnosis

Symptoms of stem girdling roots include: (1) Scorch, early fall color, early leaf drop, damage on one or two branches. (2) Abnormally small leaf size. (3) Excessive twig dieback, the appearance of large, dead, leafless branches (stagheading). (4) Thin appearance to the crown, overall stunting. (5) Little or no trunk taper at the collar. (6) Leaning (7) Susceptibility to environmental extremes and other biotic problems.

Many of these symptoms can also be characteristic of other causes, such as drought or nutrient imbalances. A plant disease diagnostic laboratory cannot identify this problem. The only sure way to determine if a stem girdling root is the cause of a problem is to examine the root system and its relationship to the tree trunk.

Integrated Pest Management Strategies:

1. Inspection. Carefully inspect the root system at the time of planting. Remove any girdling root on bare-root plants. Cut away the wrapping on balled & burlapped plants, check for girdling roots and natural root flare. Cut through any circling roots of container grown plants in a few places.

On mature trees, if any of the symptoms appear, examine the root collar by probing into the soil near the trunk flare with a stiff wire to find the depth of any stem girdling roots.

2. Planting. Dig planting holes 2 to 3 times as wide as the root ball, with sloped sides and no deeper than the root ball. In heavy clay soil dig the holes shallower than the root ball by at least 3 inches. Make sure there is no soil above the root flare. If there is soil above the flare, very carefully remove it down to the flare. Apply mulch no deeper than 3 inches and never against the trunk of the tree.

3. Ongoing care. Make sure to water a newly planted tree regularly and water any tree during drought periods. Avoid using fast–release fertilizers, they may burn tree roots. Reduce environmental stresses on established trees and add nutrients if it appears there is a deficiency. Periodically examine the root flare to make sure it appears normal. If stem girdling roots are present, gently remove the soil until you can find the root collar flare. This may need to be done by a certified arborist.

4. Pruning. Stem girdling roots are commonly removed by using wood gouges, saws or pruners if they have caused minimal stem compression. If one has caused extensive compression, removal treatment must be careful not to damage the stem. Such roots are frequently left in place when they cannot be removed safely. Again, it may be necessary to consult with a certified arborist.

5. Removal. If stem compression from a stem girldling root is more than one third to one half of the stem circumference, removal of that tree should be considered because the tree’s stability is compromised.

Selected Tree Species for the Midwest, Observed by Practitioners to Have Stem Girdling Roots

Austrian pine, Pinus nigra
Black gum tupelo, Nyssa sylvatica
Bradford pear, Pyrus calleryana
Bur oak, Quercus macrocarpa
Cherry, Prunus spp.
Crabapple, Malus spp.
Dogwood, Cornus spp.
Elm, Ulmus spp
Fruitless mulberry. Morus alba
Gingko. Gingko biloba
Green ash, Fraxinus pennsylvanica
Hackberry, Celtis occidentalis
Hemlock, Tsuga canadensis
Holly, Ilex spp.
Honeylocust, Gleditsia triacanthos
Juniper, Juniperus spp.
Littleleaf linden, Tilia cordata
Norway maple, Acer platanoides
Norway spruce, Picea abies
Pin oak, Quercus palustris
Poplar/Cottonwood, Populus spp.
Red maple, Acer rubrum
Red oak, Quercus rubra
Sawtooth oak, Quercus acutissima
Scotch pine, Pinus sylvestris
Shumard oak, Quercus shumardii
Siberian elm, Ulmus pumila
Silver maple, Acer saccharinum
Spruce, Picea spp.
Sugar maple, Acer saccharum
Sugarberry, Celtis laevigata
Sweetgum, Liquidambar styraciflua
White oak, Quercus alba
White pine, Pinus strobes
Zelkova, Zelkova sp.

List based on A Practitioner’s Guide to Stem Girdling Roots of Trees by Gary R. Johnson & Richard J. Hauer, University of Minnesota Extension Service.

Organic Strategies

Strategies 1, 2, 4, and 5 are strictly organic approaches. Using an appropriate organic fertilizers and nutrients would be a viable organic approach to Strategy 3.

More images:

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Girdling root on a cherry (Prunus) caused by mulch being piled against the trunk.
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Girdling root on Japanese tree lilac (Syringa reticulata); also planted too deep
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Girdling root on maple (Acer)
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Some girdling roots are visible on the surface; others are not
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Mulch volcanos (mulch piled against the trunk of a tree) can lead to girdling roots, while too much mulch can prevent water from reaching the roots
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Close-up of mulch volcano
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Dead spot at crown of a sweet gum (Liquidambar styraciflua) caused by an unseen girdling root
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A trunk that emerges straight from the ground can indicate a girdling root hidden beneath the soil, as the missing flare on the left side of this sweet gum (Liquidambar styraciflua)
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Girdling root on sweet gum (Liquidambar styraciflua)
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Girdling root on sweet gum (Liquidambar styraciflua)
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A tree trunk that emerges straight from the ground without any flare roots, like this ash (Fraxinus), usually indicates a tree that has been planted too deep and may develop girdling roots
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A tree planted properly should have visible flare roots as does this pin oak (Quercus palustris)
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The graft union on this ash tree (Fraxinus), visible as a swollen crown, could be mistaken for a girdling root
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A girdling root finally strangled this white pine (Pinus strobus)
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Girdling root on dwarf Alberta spruce (Picea glauca 'Conica') caused by being in a container too long.
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Girdling roots circling a maple tree (Acer)
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The roots of this maple tree (Acer) should have been cut when it was removed from the container for transplanting.


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