3 Methods for Pruning a Tree

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Reasons for Pruning a Tree

Reasons to Prune

There are many reasons for pruning trees. Pruning can assure added safety for people entering the landscape, increase tree vigor and health and will make a tree more beautiful. Value-added benefits of pruning includes stimulating fruit production and can increase the value of timber in a commercial forest.

Pruning for personal safety - Remove branches that could fall and cause injury or property damage, trim branches that interfere with lines of sight on streets or driveways, and remove branches that grow into utility lines. Safety pruning can be largely avoided by carefully choosing species that will not grow beyond the space available to them, and have strength and form characteristics that are suited to the site.

Pruning for tree health - This involves removing diseased or insect-infested wood, thinning the crown to increase airflow which will reduce some pest problems, and removing crossing and rubbing branches. Pruning can best be used to encourage trees to develop a strong structure and reduce the likelihood of damage during severe weather. Removing broken or damaged limbs encourage wound closure.

Pruning for landscape aesthetics - Pruning can enhance the natural form and character of trees and stimulates flower production. Pruning for form can be especially important on open grown trees that do very little self-pruning.

Important Note: you are trying to improve a tree's structure, especially during the early years. As trees mature, pruning will shift to maintaining that tree's structure, form, health and appearance.

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Crown Thinning

Crown Thinning
Tree Crown Thinning. USFS

Crown thinning is a pruning technique primarily used on hardwood trees. Crown thinning is the selective removal of stems and branches to increase light penetration and air movement throughout the crown of a tree. The intent is to improve a tree's structure and form while making life uncomfortable for tree pests.

Stems with narrow, V-shaped angles of attachment (Graphic B) often form included bark and should be selected for removal first. Leave branches with strong U-shaped angles of attachment (Graphic A). The included bark forms a bark wedge when two stems grow at sharp angles to one another. These ingrown wedges prevent 36-foot attachment of stems often causing a crack at the point below where the branches meet. Removing one or more of the stems will allow the other stem(s) to take over.

Branches growing off these stems should be no more than one-half to three-quarters of the diameter of the stem at the point of attachment. Avoid producing "lion's tails" or tufts of branches and foliage at the ends of branches by removing all inner lateral branches and foliage. Lion's tails can result in sunscalding, epicormic sprouting and weak branch structure and breakage. Branches that rub or cross another branch should be removed.

To avoid unnecessary stress and prevent excessive production of epicormic sprouts, no more than one-quarter of the living crown should be removed at a time. If it is necessary to remove more, it should be done over successive years.

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Crown Raising

Tree Crown Raising
Tree Crown Raising. USFS

Crown raising is simply removing branches from the bottom of the crown of a tree to provide clearance for pedestrians, vehicles, buildings or lines of sight. For street trees, the minimum clearance is often specified by municipal ordinance.

When pruning is complete, the existing living crown should be at least two-thirds of the total tree height. Example: a 36-foot tree should have living branches on at least the upper 24 feet.

On young trees, "temporary" branches may be retained along the stem to encourage trunk taper and to protect trees from vandalism and sun scald. Less vigorous shoots should be selected as temporary branches and should be about 4 to 6 inches apart along the stem. They should be pruned annually to slow their growth and should be removed eventually.

In forest timber management and to develop a higher value tree, you remove limbs from below for clear wood. Removing limbs increases wood quality which increases timber production values. Removing lower limbs can also be of significant health value ‚Äčto certain tree species. Pruning lower branches on white pines can help prevent white pine blister rust.

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Crown Reduction

Tree Crown Reduction
Tree Crown Reduction. USFS

Crown reduction pruning is most often used when a tree has grown too large for its permitted space. This method, sometimes called drop crotch pruning, is preferred to topping because it results in a more natural appearance, increases the time before pruning is needed again and minimizes stress.

Crown reduction pruning should only be used as a method of last resort. This pruning technique often results in large pruning wounds to stems that may lead to decay. This method should never be used on a tree with a pyramidal growth form. A better long term solution is to remove the tree and replace it with a tree that will not grow beyond the available space.

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Pruning Techniques That Will Cause a Tree Harm

Harmful Pruning Cuts
Harmful Pruning Cuts. USFS

Topping and tipping are common pruning practices that harm trees and should not be used. Crown reduction pruning is the preferred method to reduce the size or height of the crown of a tree, but is rarely needed and should be used infrequently.

Topping, the pruning of large upright branches between twig nodes, is sometimes done to reduce the height of a tree. Tipping is a practice of cutting lateral branches between nodes to reduce crown width. These practices invariably result in the development of epicormic sprouts or in the death of the cut branch back to the next lateral branch below. These epicormic sprouts are weakly attached to the stem and eventually will be supported by a decaying branch.

Improper pruning cuts cause unnecessary injury and bark ripping. Flush cuts injure stem tissues and can result in decay. Stub cuts delay wound closure and can provide entry to canker fungi that kill the cambium, delaying or preventing wound-wood formation.