When Snow or Ice Bows and Breaks Tree
Marianne C. Ophardt
Washington State University Extension
Area Horticulture Specialist
Heavy wet snow, freezing rain and ice can mean bowed and broken tree limbs and trunks. What causes limb and branch breakage? Certain types of trees, especially fast growing species, have "brittle" wood that is prone to breakage. This includes Chinese elm, silver maple, boxelder, and poplar. Some tree species have narrow branch angles, making them structurally weaker in situations like these. The `Bradford' cultivar of callery pear is a good example of a tree with a weak structure due to narrow branch angles.
Another reason for structural weakness in a tree is past pruning practices. Improper pruning practices, such as topping or stub cutting, leads to the development of poorly attached branches. There is a great tendency for these branches to break off the tree as they grow larger and heavier, especially when stressed by strong winds or a load of snow and ice.
Trees also become structurally weaker when wood rot develops in the trunk and main branches. Wood rot is the result of fungi, which invade the tree after physical damage occurs... through wounding, bad pruning cuts, and severe temperature damage. Severe wood rot can develop through repeated wounding and large branches that have been topped.
Some trees broke under the recent heavy snow-loads but some only bent... bending or bowing was common on young deciduous trees, as well as on certain types of evergreens trees and shrubs. The wood in these plants is more elastic, with wood bending instead of breaking. In these cases, it was merely a factor of the snow and ice and the branches yielding to the weight.
Now what can be done about the injured trees and shrubs? Let's deal with the "bent-out-of-shape" plants first. According to Dr. Ray Maleike, Washington State University Extension Horticulturist Emeritus, "When snow or ice bend branches and entire trees out of shape, the offending snow or ice should be removed immediately and an attempt made to straighten the bent branch or trunk. If the plant part isn't straightened very soon after the snow has stopped, the plant may remain bent over... permanently." Collected snow can be removed with a broom. Sweep upward to lift the snow off. However, don't disturb the branches if they're heavily weighted and brittle with ice or you have a concern about the structural integrity of your tree.
Maleike suggests trying to physically straighten the plant or branch once you remove the snow. He notes, "This doesn't always work, but it does occasionally. If the young tree or shrub has been squashed down to where it extends into traffic areas, it may have to be pruned."
Around our area there a number branches on multi-stemmed, columnar-needled evergreens, like arborvitae, that have been bent out away from the plant. Maleike indicates that these may be tied back to the main plant with a soft, non-chafing material like cotton clothesline or nylon pantyhose. The tying materials may have to be left on for 6 months or more. He notes, "Tying the plants together before the winter starts is a good preventative for this problem."
What can be done for small trees which have bowed over but have not broken or cracked? These trees can be staked until they can stand on their own again. Maleike recommends this procedure, "Drive two stakes, about six to eight inches away from the trunk, into firm ground. (Be careful not to severe major roots.) Then tie the trunk to the stake at the lowest height, which stabilizes the tree in an acceptable upright position. A nonchafing tying material must be used."
The stakes should not be left on indefinitely. They should be removed as soon as the tree can stand by itself again. This should be within the first growing season after the "bowing" occurred.
Trees with broken branches don't need immediate attention. However, it's advisable to prune off broken branches as soon as the weather and circumstances allow. Prune damaged branches back to another branch or the main trunk if necessary... don't make flush cuts and don't leave branch stubs. On large branches this cut should be made to just outside the branch collar. Be sure to follow recommended tree pruning practices. When power lines, large limbs, or main branches complicate the matter, contact a trained and certified arborist.
With the breakage of limbs, sometimes bark is torn on the larger limbs or the main trunk. To help the tree, the torn bark should be carefully trimmed with a sharp knife to make a smooth, rounded edge to the wound. Cut only the bark and not into the wood. No wound dressing materials are recommended for bark wounds or pruning wounds.