Garden Talk - Winter pruning is right for oak trees
For almost everything in our landscapes, pruning is a mild-weather activity. The one crucial exception is oak trees. Winter pruning – that is, December through February – reduces the risk of oak wilt infection.
That reduced risk is something to take seriously. Oak wilt is a lethal fungal disease. It spreads from infected to healthy trees by means of sap-feeding beetles. These beetles are very active through the spring and early summer months. During these same months, infected trees will be producing fungal material called spore mats.
Spore mats release a fruity odor that is attractive to sap beetles. As the beetles feed, spores may adhere to their bodies. Sap from pruning cuts made in the spring or early summer can attract the beetles, who will bring with them fungal spores that then get into the fresh cut and infect the oak tree.
With that information as background, it is clear that winter pruning is a good idea. Here, then, is the technique needed to make the pruning cuts efficient and effective.
First, be aware of certain key terms relevant to the structure and pruning of oak trees. The branch collar is the swollen area at the base of a branch. The branch bark ridge is the rough and dark bark ridge that separates the branch from a main branch or trunk. Pruning just beyond the branch collar and the branch bark ridge helps to retain the tree’s natural defense mechanisms and promote callus formation.
If you will need to prune branches greater than 1-1/2 inches in diameter, use a three-cut procedure. Cut upward six to 12 inches from main branch or trunk, but go only 1/3 of the way through the branch. Make your second cut one to two inches beyond the first, sawing downward from the top of the branch. The weight of the branch will cause a break at the pivot point between the two cuts. Then make the final cut just beyond the branch collar and branch bark ridge to complete the process.
If you are able to prune oaks in winter, do not apply any paint or wound dressing. Only in the case of emergency spring or summer pruning (for example, because of storm damage) should paint be used. In such a case, cover the cuts with a latex house paint within 15 minutes of making the cuts. This practice is a necessary step for preventing oak wilt transmission in spring or summer.