Extend tree life by pruning at the right time and in the right way.

PHOTO: BARTLETT TREE EXPERTS 

Winter is a popular time to prune trees. Leaves have fallen, and the tree structure is clearly visible. With a direct sightline to the tree’s interior growth habits, it is often easier for an arborist to identify structural issues and make sound pruning decisions. Though there are many benefits to pruning during winter, the first question when making tree maintenance decisions should not be when, but rather why.

Timing and technique are critical in all facets of tree care, but it is important to step back and first consider the goal of the work and the specific needs of the plant. When pruning, in winter or any season, consider all of the factors involved before making cuts that could result in long-term damage if executed incorrectly.

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? What are the customer’s expectations?

Answer these questions before cutting. Pruning alters both the form and growth of the plant. When trees are pruned, less foliage is available to support growth and development. Removing even one large limb can be significant enough to injure a tree permanently. Never prune without a clear purpose.

A reason to prune

Removal of dead, dying or diseased branches promotes tree health. Virtually all trees within our communities benefit from this type of periodic cleaning. Removing weak branches also improves safety. Give particular attention to limbs that overhang homes, driveways, parking areas or sidewalks.

Trees and shrubs often serve a specific purpose in the landscape and pruning can preserve that function. For example, pruning can help maintain a dense hedge used as a border or barrier on a property. In species that produce fruit and flowers, pruning can encourage fruit or flower development.

Don’t forget that appearance is a major purpose of trees and shrubs in most landscapes and is often essential to a plant’s usefulness. Pruning helps control size, improve a tree’s form and keep plants correctly proportioned.

For young trees, pruning aids in the development of a desirable and stable form. Also, pruning when the tree is young prevents most structural defects from developing. Proper care establishes a strong, central stem and maintains branch size and distribution.

Whatever the objective, minimize wound size and loss of live branches. Younger trees fare somewhat better when live tissue is removed than mature trees. Tree condition can help govern to what extent a tree is pruned. Industry standards suggest that you remove no more than 25 percent of the crown. Even less may be appropriate for mature trees or trees showing signs of distress.

A season to prune

You can perform routine pruning any time of year. However, pruning during dormancy results in a vigorous burst of spring growth. Fresh pruning wounds are exposed for only a short period 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, growth is redirected to buds on the remaining branches.

In addition to knowing where and how to cut, keep your pruning implements sanitized to prevent the spread of disease from one plant to another. PHOTO: BARTLETT TREE EXPERTS

Winter pruning can also play a role in managing insects and diseases. Oaks are one example. Pruning wounds made during spring, when oak wilt diseases are active in many areas of the United States, 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 the tree 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 to prune. 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.

For apples, peaches, pears and many other fruit trees, winter pruning will improve light penetration, yielding more fruit. Disease management is again a consideration as spring or summer pruning increases exposure to the bacterial disease fire blight.

The ability to better see the tree’s form in winter is certainly a consideration for all species – young and old alike. Issues that might otherwise go undetected are more visible when no leaves obscure the branches.

The four basic techniques

When the needs of the plant have been established and it is time to prune, four basic pruning techniques are used. Depending on tree requirements, client expectations and budget, these techniques can be used alone or in combination to achieve pruning objectives.

1. Cleaning is the removal of defective branches including those that are dead, dying, diseased and rubbing. Cleaning reduces the risk of branch failures, improves plant health and enhances tree appearance by removing branches that are unsightly, unhealthy and unsound.

2. Thinning is the removal of live, healthy branches on trees with dense crowns. This improves light penetration and air movement and decreases wind resistance, thus reducing pest infestations and minimizing the risk of storm damage. Thinning is most commonly needed on young, rapidly growing trees. On slower growing mature trees, it is mainly used when weight reduction is needed on individual branches to compensate for structural defects.

3. Reduction involves reducing the height or spread of the crown or individual branches. It is needed when trees are growing close to buildings, other trees or wires. Reduction may also be necessary to prevent or correct storm damage and to shorten errant branches to provide a more desirable shape. Certain species, including beech and sugar maple, respond poorly to reductions, so give consideration to the ability of the species to tolerate this technique.

4. Raising is the removal of lower branches to provide clearance for buildings, vehicles or pedestrians. Branches can either be removed at the trunk, or downward growing branches can be removed at the parent branch.

The tree guides the decision-making process for choosing the correct technique. For example, if the tree has dead branches, clean it. If the tree is overly thick, thin it.

Right time, right place

While technique is critical, making informed pruning cuts is no longer about only the correct method for removing branches. Even if you knew the surgeon was a skilled expert, would you undergo a medical procedure without first understanding the procedure’s purpose? So it should be with tree pruning, especially when a significant impact to overall tree health is considered.

Winter is a good time to prune because, on most trees, there are no leaves, and it is easier for an arborist to identify structural issues. PHOTO: BARTLETT TREE EXPERTS

Knowing why cuts will be made is the basis for determining which cuts should be made where and at what time. This practice is best started when a tree is young but will benefit the tree at any age.

Dr. Thomas E. Smiley is a plant physiologist and soil scientist at Bartlett Tree Experts’ research laboratories in Charlotte, North Carolina. He has more than 30 years of experience in arboricultural research. Tina McNulty is a marketing manager at Bartlett Tree Experts where she works to promote awareness of the tree care industry and the importance of proper tree maintenance. Learn more at 877-227-8538 or www.bartlett.com.