Winter offers few garden activities other than filling birdhouses and carefully watching dormant plants for signs of awakening as spring approaches. However, the winter dormancy is the ideal time to prune wood plants.
When trees and shrubs are inactive in hibernation, pruning can now avoid disrupting the many processes that take place during the growing season.
Pruning is one of the most beneficial cultural practices we can use in the landscape to help trees and shrubs maintain a healthy canopy and develop good branch structure. The list of cutting benefits is long, including improved disease and insect resistance and other health benefits, as well as simple aesthetic improvements by creating a more balanced plant or better view of other landscaping or hardscaping.
The importance of pruning shade trees cannot be emphasized enough given its impact on tree canopy structure. Proper pruning can have a lasting effect, building trees for life-long limb health while reducing “fixable” problems before those problems threaten limb failure.
Many of us often don’t think about pruning shade trees until they are the large, mature specimens that tower over driveways, roofs, and other important aspects of the landscape. However, properly applied pruning when a tree is young can correct many structural weaknesses that may prove “irreparable” after a tree has matured.
For example, most of the urban trees we see in parks, along boulevards, and around houses have a cluster of branches that protrude from the trunk at a very similar height, often about 6 to 8 feet above the ground, in all directions radiate.
This becomes a structural problem as the tree matures and many large limbs are attached in close proximity. All of these closely related branches are at risk of failing in the everyday stresses of wind and the many thunderstorms that our region experiences each year. They simply do not have as strong a bond with the trunk as limbs that are more evenly distributed across the trunk, and together they form a weaker section of the tree trunk.
This can often cause one or more limbs to peel off, but can also contribute to trunk failure during more extreme storm events. All of this structural weakness could easily have been fixed in the tree’s early years with a simple corrective cut to properly place the permanent limbs up and down the trunk.
To take another example, a young tree can often be pruned very easily, creating a more dominant central leader, or the tallest branch of the tree, which is the most active growth point on top. Establishing a dominant central conductor early in a tree’s life by removing competing limbs can help the plant focus its growth upward rather than outward. Essentially, you get a taller shade tree much faster that can provide valuable shade much sooner.
In addition to focusing and optimizing growth, an established central market leader that is free from competition with neighboring limbs also creates an overall stronger and more resilient canopy structure. It prevents future damage to the upper canopy from storms and other loads by establishing better branch spacing and preventing the formation of weaker branch attachments on the trunk.
I often get questions about why a tree needs help growing. Don’t trees grow well in a forest without pruning? Haven’t trees done that in millions of years? The answer lies in the fact that urban trees don’t usually grow under pressure from neighboring plants like trees in the forest do.
Since the light in a forest roof is severely restricted, trees have to grow upwards quickly in order not to be in the shade. The resulting canopy structure typically creates widely spaced branches with a strong central guide line. In contrast, urban trees that are “openly” and free of competition develop differently and often need to be corrected.
If you are interested in learning more about pruning young trees and all other aspects of tree care, the International Society of Arboriculture has a wonderful website of information. Visit the Tree Owner Information tab on treearegood.org for pruning information, or use the Find Arborists tab to identify certified arborists in our area who can meet all of your tree pruning needs can.
Ryan Pankau is a UI Extension horticultural educator serving Champaign, Ford, Iroquois, and Vermilion Counties. This column also appears on his ‘Garden Scoop’ blog at go.illinois.edu/GardenScoopBlog.