Winter Pruning: When and Why

Winter is a good time to prune trees. With the leaves gone, a tree’s structure is clearly visible. This provides a direct sightline to the tree’s interior growth habits. As such, it is often easier for an arborist to identify issues and make sound pruning decisions. Since pruning alters both the form and growth of the plant, it’s important to consider all the factors involved when undertaking winter pruning.

Some things to think about: Is the tree close to a building, walkway or power lines? What is its condition? Are any structural defects or storm damage present? What are the landscape functions provided by the tree and how will pruning impact those functions? Is the tree too dense? Does it need shaping? In essence, why is important to prune the tree and when should that happen?

winter tree pruning
Pruning cuts impact the structure and growth of a tree and, as such, should be executed with thought and care.

A Reason to Prune

Removal of dead, dying or diseased branches helps promote tree health. Virtually all urban trees benefit from this type of periodic cleaning. Improved safety also results when weak branches are removed. Limbs that overhang buildings, parking areas or walkways should be given particular attention. Winter pruning can address these tasks, making trees healthier and safer.

Beyond routine pruning, consider the specific purpose of trees and shrubs in the landscape. Pruning may be critical to preserving that function. For example, pruning can help maintain a hedge used as a border or barrier on a property. Appearance is another major purpose of trees and shrubs in most landscapes. Pruning can help control size, improve a tree’s form and keep plants well-proportioned – enhancing the overall appearance of the property.

Indian hawthorn pruning cut
When used as a border, shrubs and hedges need regular pruning to maintain their size and shape.

For young trees, pruning aids in the development of a desirable and stable form. Most structural defects that occur in older trees can be prevented by pruning when the tree is young. Proper care can establish a strong, central stem and help maintain branch size and distribution.

Whatever the objective, care should be taken to minimize wound size and loss of live branches. Younger trees fare somewhat better when live tissue is removed than mature trees. Condition of the tree can help govern to what extent it is pruned. Industry standards have specified that no more than 25% of the crown should be removed. For mature trees or those showing signs of distress, even less may be appropriate.

A Season to Prune

Pruning during dormancy (in winter) is common because it results in a vigorous burst of spring growth. Fresh pruning wounds are exposed for only a short period of time before new spring growth begins. Additionally, because there are no leaves to manufacture sugar in the winter, there is no interruption to the tree’s growth cycle. It is less stressful for the tree and, as spring begins, all growth efforts are re-directed to buds on the remaining branches.

Pruning during winter can also play a role in managing insects and disease. Oaks are one example. Pruning wounds made during spring, when oak wilt diseases are active in many geographies, allow spores to infect the tree. Beetles that carry Dutch elm disease spores can also be attracted by fresh cuts. Pruning when these diseases are not active inhibits their spread. Understanding of the species and associated insects and disease problems in your area is crucial when making these pruning decisions.

Timing is particularly important for species that produce fruit or flowers. If the goal of pruning is to enhance flowering for trees that bloom in mid to late summer, winter or early spring are the best times. This includes species like rose of Sharon and crape myrtles. However, for plants that bloom earlier in the growing season such as magnolia or azalea, prune after they finish blooming.

Right Time, Right Place

Even if you knew a surgeon was a skilled expert, you wouldn’t undergo a medical procedure without first understanding the purpose. So it should be with tree pruning, especially when the significant impact to overall tree health is considered. Knowing why cuts will be made is the basis for determining which cuts should be made. The ability to better see the tree’s form, and identify issues that might otherwise go undetected, makes winter the ideal time for an initial evaluation.

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