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Potential for winter damage to trees and shrubs

By Al Cooke, Ag Extension agent
Posted Thursday, February 1, 2007

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Pittsboro, NC - As I listen to multiple scenarios of “wintry mix” descending into our neighborhoods, as I sit now and watch the snow accumulating, I am reminded of the most significant threat that winter weather provides to plants: it’s not cold; it’s breakage.

Snow accumulating on trees and shrubs is usually not a significant problem initially. As it builds up and bends branches, it tends to fall off also. However, wet snow in the south tends to accumulate more than the dry snow in other locations. Later problems can occur as snow (or ice) starts to melt. Some of it may come sliding off roofs and dump a lot of weight in a small area in a split second. Sometimes damage can be avoided by leaning a sheet of plywood against the house to protect that favorite Daphne from damage. On the other hand if the plywood slides with the downfall, it may make the problem worse by just adding more weight.

Freezing rain can be a more significant problem. As supercooled rain contacts surfaces at or below freezing, ice forms. The accumulation of ice can significantly increase the weight of a limb, and it doesn’t slide off readily. Accumulations of ice have been estimated to increase the weight of a branch as much as 30 times. As little as ¼ inch of ice can begin to cause small limbs to break. At ½ inch accumulations, large limbs break.

What you can do at this point is not much. Immediately after a snowfall it is sometimes helpful to use a broom or rake to lightly brush snow from sagging plants. Removing the weight will allow branches to more quickly return to their natural stature. Once the snow starts to thaw and then refreezes, that action probably does more harm than good. And it is usually counterproductive to attempt breaking ice off branches. You’re just as likely to break the branch.

Such weather does, however, serve as a reminder of preventive actions that could have been taken and may be worth considering in the future. Among these are tree selection and tree maintenance.

Tree selection can include seeking trees that are structurally better equipped to hold up extra weight. Branches with narrow angles to the trunk such as Bradford pear are much more susceptible to breaking. Trees whose branches are more wide spreading such as the Aristocrat pear have stronger branch attachment and hold up better.

Trees more likely to sustain damage include American linden, black locust, Bradford pear, hackberry, green ash, honey locust, pin oak, and silver maple.

Some more resistant trees include sweetgum, baldcypress, black walnut, ironwood, catalpa, ginkgo, Kentucky coffee tree, littleleaf linden, silver linden, and white oak.

Tree location is also a factor to be considered. If it has room to develop a full crown rather than a one-sided crown created by crowding, the tree tends to have stronger limb attachment. Trees close to utility lines often are pruned to protect the lines but also develop more weight on the opposite side. (For a list of small trees suitable for use under utility lines, see
http://www.ces.ncsu.edu/depts/hort/hil/hil-8616.html)

Good tree management can also reduce damage. A competent arborist can advise if crown reduction is appropriate. (Do not have a tree topped! It only leads to branches with weaker attachment). It is always appropriate to remove dead limbs, but often requires professional expertise to accomplish safely. For help in selecting a competent arborist, see “How to Hire a Tree Service” at http://www.ces.ncsu.edu/chatham/ag/homehort/GreenInd/master.html

If you get damage to trees from the current “wintry mix,” consider the hazards before taking any action. Storm damage is probably the most hazardous way to learn how to use a chainsaw, and the damage it does is not pretty. If you have hazardous
limbs on the ground, on wires, or hanging overhead, get competent help. Secure the area to protect people, and wait for qualified help.

Damaged trees may need remedial work for long-term health. Again, a competent arborist is your best ally for determining what needs to be done.

 
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