Protect young trees from winter injury
By Tracey Payton Miller
I was outside painting this weekend, when I began making a mental list of things to do outside before winter hits. My newly planted trees are some of my most favorite and expensive additions. When I lose a plant, I always worry there was more I could have done to help it survive. Since painting gives you a lot of time to think, I began thinking about all the plants I installed this year.
I dug a wide hole for the tree, two times or more the diameter of the rootball. Some of the roots were circling, so I scored them with my pocketknife. I made sure the hole was not too deep, that the rootball would be a few inches above grade. I backfilled the hole with the native soil and tamped it down. I then top-dressed the planting with some compost and watered it thoroughly. I did everything needed, so there should not be any problems. Then it hit me: I forgot to wrap the tree to protect it from southwest injury.
Southwest injury, also known as sunscald, is a major winter problem for new transplants or thin-barked trees. During the late fall and early spring, Oklahoma gets frigid temperatures, following mild sunny days. This is when the injury happens. The sun is at a lower angle in the sky, to the south and southwest. Since the canopy is bare of leaves, the trunk is unprotected from the warming sun. As the trunk warms, the cells "thaw." Then temperatures plunge once again as the sun begins to sink in the sky. This causes the cells to freeze again and rupture.
This damage is devastating to a young tree. The symptoms of sunscald are a vertical split or "puckering" that will be present on the southwest side of the trunk. However, you will not notice the damage until several years later, when it is too late. Therefore, it is important to protect young trees for the first several winters to prevent southwest injury. Protective coverings for the tree consist of materials to shade the trunk. The shade will prevent hardened cells from thawing.
Wrap trunks of tree species such as maples, fruit trees, willows, ash, locust, willow, and thin-barked oaks from November to March. Several materials are available to protect trunks. One of the most common materials is a plastic spiral wrap that encircles the trunk. These wraps have holes to allow air movement and are less likely to harbor pests. There are also non-perforated paper wraps that can be used, but be sure to inspect the trunk regularly for water logging or insects. Another option is to wrap the trunk with burlap and secure it with twine. However, it is very important to remove the burlap and ties in spring, so as not to girdle the tree. Trunk wrapping materials are available at your local garden center or nursery.
As a homeowner, it is very unfortunate to go through the motions selecting a tree, planting it, watering it, and caring for it to have it injured by something that is easily prevented.