Fall is a time to wrap up many landscape chores before the cold of winter arrives. If pruning trees and shrubs is on your to-do list, you may think twice. Research indicates fall may not be the best time for this task.
Woody plants obtain energy in the foliage needed for growth. As the weather cools and daylight decreases, sugars and other nutrients move from the leaves into the branches and trunk. If you prune before the leaves drop, you remove this food source, decreasing the amount of stored energy.
According to research from Penn State Extension, fall pruning reduces the cold hardiness of woody plants. Pruning a branch too soon can delay dormancy and stimulate plant growth.
Whether winter injury occurs is dependent on several factors. Injury is most common when there is a sudden drop in temperatures following pruning. The plant does not have time to prepare internally for winter.
The tree species also has an effect. Woody plants that are marginally hardy in our climate are more susceptible to winter injury. Genetically they are not programmed for more extreme weather conditions.
Heavy pruning affects the tree’s dormancy more than a light pruning — less than 10% of the total wood.
There is an adage that says “prune whenever your pruners are sharp,” but we may want to think twice based on this research. As with most rules, there are always some gray areas. In the case of dead wood, remove it anytime of year, as it is not alive and does not manufacturer energy.
For safety reasons, any broken, damaged or hazardous limbs should also be removed right away. An example would be a low-hanging branch above a sidewalk that could poke someone in the eye. Safety is always an overriding factor.
Pruning is best accomplished when the trees and shrubs are fully dormant. Dormancy happens after leaf drop and several hard freezes in the fall. The lack of foliage exposes the structure of the tree, making it easier to decide which branches to leave and which to prune. Reduced visibility when the tree is leafed out may make choices more difficult.
Pruning during winter reduces the spread of insects and diseases to the open wound, as they are not active. Spring is also a time of rapid growth. Making the cut in winter prior to spring’s arrival stimulates new growth to help the plant seal off the wound made by the cut.
Go ahead and make a few cuts here and there on woody plants. Remove the dead, damaged and hazardous limbs. But give the tree time to take in all its energy for growth and become fully dormant before undertaking any major pruning efforts.
Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Got a question for him or other university extension experts? Email them to email@example.com.