Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES
Girdling Roots – A Problem of Shade Trees
Trees
can slowly weaken and die over a period of years or decades because of root
girdling. Roots begin to grow around the
main stem of the tree and cut off or restrict the movement of water, plant
nutrients and stored food reserves.
Over
time, growth of the branches on the side of the plant affected by the girdling
will be slowed. As injury progresses,
leaves will become smaller and lighter green, fewer leaves will be produced and
eventually the branch will begin to die back.
Death of the entire plant can occur in five to 20 years, watering,
fertilizing and pruning will do little to correct the problem.
Certain
trees are more prone to this problem than others. Lindens, magnolias, pines and maples other
than the silver maple are susceptible to root girdling. On the other hand, oaks, silver maples, ash,
and elm are well known for their ability to form functional root grafts and are
rarely adversely affected by girdling roots.
Normal
trees have a gentle trunk flair or buttress at their base (Fig. 1). Trunks that grow straight up from the ground
as though they were a telephone pole can be suspected of having girdling roots
(Fig. 2). Trunks with a straight side or a concave depression on one side may
also have a girdling root (Fig. 3).
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Figure 1 |
Figure 2 |
Figure 3 |
Development
of girdling roots is not well understood but is normally thought to be the
result of unfavorable conditions which prevent roots from growing out in a
normal spreading manner. A good example
is a container-grown plant, where the roots are often forced to grow in a
circular fashion. If these trees are not
pruned at the time of transplanting, this growth pattern can cause girdling
roots.
Root
pruning is an absolute
must for any container-grown tree or shrub at the time of transplanting. Three
to five slashes are made vertically down the football and about an inch into
the rootball.
One or two slashes into the bottom of the rootball
are made at a depth of three to four inches. Some people go further by fraying
out the pruned roots.
Restricted
root space--such as tree pits in urban areas--also may result in
girdling roots. There
is some suggestion,
too, that constant mulching--a desirable practice in many respects--may cause
the formation of girdling roots.
For
plants susceptible to root girdling, an inspection should be made when the tree
is approximately six inches in diameter. A positive diagnosis can only be made
by exposing the roots. Soil is carefully removed to a depth of at least 12
inches, with care taken to prevent serious mechanical injury to the roots. If
girdling roots are found on a plant with known susceptibility, the girdling
root must be removed, a process normally carried out with a chisel.
Removing
a girdling root is a wound in its own right. Yet, while the correction of the
problem can kill the desirable plant, the likelihood of the plant dying is
greater if no action is taken. Conducting a preventative inspection when the
tree is about six inches in diameter will assist in correcting the problem
before it becomes serious.
If the
inspection reveals girdling and a considerable amount of damage, the most
prudent move may be to replace the tree. Spending money on a weakened tree
which subsequently dies can be an extremely frustrating experience; because
correction of this problem is so labor intensive, the costs and benefits should
be weighed carefully prior to making any decisions.
Information obtained through the Ohio State Extension Factsheet HYG-1139-94
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES