The leaves have all been raked up, it’s cold outside, and maybe there’s a layer of snow on the ground. While it seems like your work maintaining your trees is done as winter sets in, it is an ideal time to prune many of the trees in our landscapes. With the leaves off the trees, it becomes easy to view the interior of the tree canopy and its branching structure, allowing you to see where to prune and how much to prune. The cold temperatures also mean less concern about pest and disease issues associated with pruning cuts (e.g. oak wilt), as pests and disease are often in a dormant state through the winter.
Before getting out the pruning saw, you will want to first evaluate the tree to see what pruning may be needed. Start by looking for dead, dying, or broken branches, as well as rubbing or crossing branches. Dead and dying branches should be pruned out, and broken branches pruned back to an appropriate location below the break. Where there are rubbing or crossing branches, it is a good idea to remove one of the two branches in contact with each other. Left as is, continued rubbing can wear through the bark providing a pathway for pests or disease to enter the tree.
Further inspection should look at branch spacing and branch unions. Branches should be spaced fairly evenly, both vertically as well as radially around the trunk. Branch unions with wider angles that are more perpendicular tend to be stronger branch attachments, standing up better to forces like strong winds. In contrast, tighter angled “V” shaped unions are weakly attached, and more prone to breakage and failure in strong winds. Branches attached with these tight “V” unions should be considered for pruning, especially if these branches are still smaller. Over time, these tight “V” unions can lead to the development of co-dominant stems. Co-dominant stems are formed when two branches that are about the same diameter come together to form a tight V shaped union. Over time these two stems will get larger in diameter, applying pressure to each other until one stem breaks out, usually in a storm or high wind event.
Once you evaluated your trees in the winter, you might decide they need to be pruned, either by a professional arborist or yourself, as long as you can do so safely. Never climb a tree unless you have been trained to do this work and are using ropes and safety equipment. As a good rule of thumb for safe pruning, if you can’t reach it from the ground, you should call a professional arborist. If you plan to prune your trees yourself, be sure to read up on how and where to make good pruning cuts (https://extension.psu.edu/pruning-landscape-trees). Some worry about species, such as maple, birch, beech, and elm, which “bleed” when pruned in the winter, but it is only sap flowing from the pruning and it does not harm the tree.
If you don’t feel confident in your own evaluation, winter is also a good time to have an arborist evaluate and prune your trees as it is their slower season. Who knows, you might even get a better price during the winter months. Just make sure you find someone who is knowledgeable, like an ISA Certified Arborist (https://www.treesaregood.org/findanarborist), and will not “top,” (https://extension.psu.edu/dont-top-trees) “shape,” or otherwise damage your tree.
By Brian Wolyniak, Ph.D., Extension Educator, Renewable Natural Resources/Urban Forestry.
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