Principles & Practices for Pruning Trees

Proper pruning can offer trees several benefits. It can increase flowering, fruit production, promote healthy new growth, increase sun light and air circulation, and maintain a desired shape and/or size. Understanding that each plant in the landscape has its own growth habit and pruning requirements is important. It is necessary to prune trees that are over-grown, crowd other plants, or limits the view from windows. Plants damaged by insects, diseases, or freezing injury generally benefit from corrective pruning. On the other hand, improper and/or pruning at the wrong time of year may result in poor plant development and reduction in flowering, and may increase susceptibility to insects, diseases, or winter damage. It is important to learn and understand the three T’s of proper pruning: tools, timing, and technique.

Pruning Tools

Pruning tools are available in a wide range of brand names, styles, and prices. When purchasing tools, shop for quality and durability over price. Look for tool manufacturers that provide replacement parts and offer warranties against faulty materials and workmanship.

Hand-held pruning tools can accomplish most pruning tasks. These include hand pruners, lopping shears, pruning saws, pole pruners or hedge shears. Hand pruners are recommended for cutting small twigs and branches up to one-half inch in diameter. There are two basic types of hand pruners: Scissor-action also called bypass pruners have a sharpened blade that cuts by gliding against a thicker sharp blade. Anvil-action pruners have a sharp blade that cuts against a broad, flattened, grooved blade. Scissor-action pruners usually cost more than anvil-action type, but they make closer, smoother cuts. Anvil-action pruners can make larger cuts easier than scissor-action pruners.

For larger branches, one-half to 1½ inches in diameter, lopping shears are best. Lopping shears sometimes called loppers, are like scissor-action hand pruners except they have larger blades and long handles for increasing leverage to cut through larger branches. When using loppers, cut in one smooth stroke to avoid injuring the branch.

For branches larger than 1½ inches in diameter use a pruning saw. Pruning saws have a narrow blade for easy maneuvering and coarser points or teeth than a common carpentry saw. Most pruning saws also have a curved blade that cuts on the draw stroke, pulling the blade toward you.

For branches that are out of reach, consider using a pole saw. A pole saw typically has both a cutting blade and a saw blade. The cutting blade operates in similar fashion to the by-pass pruners using an extension mechanism. The operator is standing on the ground and pulls on a long rope or lanyard in a downward motion. This causes the blade to go across the branch and cut it off. The pole is typically constructed from either fiberglass or plastic. Some poles fit together in three 6-foot sections, while newer models have a telescoping type of extension. Because of the risk of electrocution, avoid using aluminum-handled pole pruners near power lines.

Use hedge shears for a neatly trimmed appearance. Hedge shears can be operated manually but are also available as battery, gasoline or electrically powered. Do not attempt to cut large branches with hedge shears.

To keep all pruning tools in good shape, sharpen and oil their blades at the end of each season. When sharpening loppers, hedge shears and scissor-action hand shears, sharpen only the outside surfaces of the blades so the inside surfaces remain flat and slide smoothly against one another. It is best to have pruning saws sharpened by a professional. Apply oil to the blades by wiping them with a cloth saturated in household oil, and treat wooden handles with linseed oil.

Pruning Time

Flowering ornamentals form their flower buds at different times of year, therefore, pruning times must be adjusted accordingly. Many spring-flowering trees such as dogwood and redbud set flower buds in the fall, so pruning during the fall and winter months eliminates or decreases their spring flower capabilities. Plants, such as crape myrtle, that typically flower during the summer form flower buds on new growth and can be pruned during the winter with no effect on their flowering.

As a rule, plants that flower before June 1 should be pruned after they bloom while those that flower after June 1 are considered summer-flowering and can be pruned just prior to spring growth. For additional information on suggested pruning times for selected flowering trees and shrubs, refer to the fact sheet, HGIC 1053, Pruning Shrubs.

Ornamental plants that are not grown for their showy flowers should be pruned during the late winter or early spring. Pruning may occur during the summer, however, avoid pruning 10 weeks or sooner to your areas first hard frost date. Pruning late in the season produces tender new growth that may not be sufficiently hardened and venerable to frost damage

Certain shade and flowering trees tend to bleed or excrete large amounts of sap from pruning wounds. Among these trees are maple, birch, dogwood, beech, elm, willow, flowering plum, and flowering cherry. Sap excretion from the tree is not harmful, but it is unsightly and may attract stinging insects. To minimize bleeding, prune these trees after the leaves have matured. Leaves use plant sap when they expand, and the tree excretes less sap from the wound.

Pruning Technique

It is important to understand why one pruning technique is preferred over another and why cuts are made the way they are for a particular plant species. The terminal bud (the bud at the end of a branch or twig) produces a hormone called auxin that directs the growth of lateral buds (buds oriented along the side of the branch or twig). As long as the terminal bud is intact, auxin suppresses the growth of lateral buds and shoots below the terminal. However, when the terminal bud is removed, by pruning, lateral buds and shoots below the pruning cut receive the auxin, which result in vigorous growth. Most of the new growth always occurs within 6 to 8 inches of the pruning cut.

Prune Plants Either by Heading Back or by Thinning

Heading back also referred to as “stubbing trees” is rarely warranted in the landscape and often results in undesirable multiple leaders or trunks. When pruning beneath power lines or clearing a tree from interfering with a structure, always prune back to a fork where there is a live branch at least half the diameter of the limb being removed. This technique is called “drop-crotching.” After several months, prune out all sprouts growing in response to the cut. Never “hat-rack” a landscape tree by cutting all of its branches back to an arbitrary length. This type of pruning has no place in horticulture and often kills the tree.

Thinning by cutting selected branches back to a lateral branch or the main trunk is usually preferred over heading. First, remove branches that are rubbing, crossing over each other, dead, diseased, or dying. Removing upright branches creates a more spreading crown while removing horizontal branches results in an upright form. If further thinning is desired, remove branches back to major limbs to create an open crown. This is a specialized technique that is best performed by a professional arborist. Space remaining branches along the major limbs so that each one has room to develop. Trees with properly thinned crowns resist wind damage better than unpruned trees.

Making the Cut

When a branch is cut back to the main trunk, to a lateral branch or to a lateral bud, a higher concentration of hormones in these areas causes the wound to heal rapidly. When a stub is left, the distance from the hormonal source increases and the wound heals slower, if it heals at all. Insects and diseases may enter the cut portion of a stub and cause it to die back. Therefore, whether pruning a small twig or a large branch, avoid leaving a stub by always cutting back to a bud, a lateral branch or the main trunk. When pruning back to a bud, make the cut at a slight angle just above the bud. This allows moisture to flow readily off the wound. However, avoid making the cut at a sharp angle as this produces a larger wound.

Selective Pruning of Branches

Become familiar with the shape and form of the tree before removing any live branches. In many landscapes, it would be inappropriate to change the tree’s growth habits. Instead, prune to enhance and encourage the natural shape of the tree. This consists of removing dead, diseased, or broken twigs and branches. The next step is to study the tree’s form and select the best spaced and positioned permanent branches and remove or shorten the less desirable ones. To shorten, use thinning cuts. Permanent branches should be spaced 6 to 24 inches apart on the trunk, depending on the final mature size of the tree. On smaller trees, such as dogwoods, a 6-inch spacing is adequate, whereas spaces of 18 to 24 inches are best for large maturing trees like oaks. Remove fast-growing suckers that sprout at the base of and along tree trunks or on large interior limbs.

To prune a young tree to a single leader, the stem that will become the main trunk, locate the straightest and strongest leader to retain. In shaping the tree crown, remove lateral branches that are growing upright. If left these lateral branches will compete with the leader and form a weak, multi-leader tree. Most trees can grow with a single leader when they are young, however, the growth habit of some species will change to a multiple leader spreading form at maturity. Branches that are less than two-thirds the diameter of the trunk are less likely to split than larger branches.

When training a young tree, prune back branches below the lowest permanent branch 8 to 12 inches from the trunk as these are temporary branches. Remove any lower branches that are larger than a quarter-inch in diameter. By keeping the smaller diameter branches on the trunk until they reach 2 inches in diameter (measured 6 inches up from the ground) the tree will grow faster and develop a thicker trunk. This will protect the tree from sunburn, vandalism, and/or accidental damage. Removing the lower branches too soon will result in a poorer quality plant.

Once the trunk and main branches of the tree are established, some annual maintenance pruning will be required. Each tree is different in its growth habit, vigor, and pruning requirements. Some general considerations that may help direct proper pruning decisions are:

• Remove branches that have narrow crotch angles. A major limb growing at a narrow angle to the main trunk (less than a 45 degree angle) is likely to develop a weak crotch and may split during heavy winds and ice loads.
• Remove branches that grow inward or threaten to rub against nearby branches.
• Remove branches that grow downward from the main limbs, which may interfere with mowing and other maintenance practices.
• Remove branches with insect, disease, ice, or wind damage. Damaged branches will require pruning at the appropriate location. Prune branches of pear or loquat damaged by fire blight disease several inches below the infection. To prevent spreading the disease, sterilize pruning tools between cuts by dipping the blades in isopropyl rubbing alcohol or a solution prepared from one part household bleach to nine parts water. Once all the pruning is completed be sure to lightly oil the pruners to prevent them rusting from the alcohol or bleach solution.
• Remove vigorous shoots, suckers, upright succulent shoots along the main branches from ornamental pear, cherry, crabapple, plum, and other trees. These shoots starve the tree of valuable nutrients and detract from the tree’s overall appearance. Remove them while they are young.
• Remove upright shoots, which compete with the main trunk for dominance. Remove these shoots if maintaining a conical or pyramidal growth habit is desired.

Removing Large Tree Branches

Branches larger than 1½ inches in diameter require three separate cuts to prevent trunk bark stripping (Figure 2). Make the first cut on the underside of the branch approximately 15 inches away from the trunk. Cut until the branch starts to move in a downward direction and before the saw is bound in the branch. Make the second cut in a downward direction from the top of the branch approximately 17 inches from the main trunk. This will cause the limb to split cleanly between the two cuts without tearing the bark.

In the above photo the three-cut method was not followed, which resulted in damaging the tree. In this example, the branch was cut all the way through from the top. As the branch gave way under its own weight, the bark on the lower side of the branch tore away from the trunk wounding the tree.

In order to properly cut the limb, support the remaining stub with one hand while cutting it away from the tree. This final cut should begin on the outside of the branch bark ridge and end just outside of the branch collar swelling on the lower side of the branch. The branch bark ridge is usually rough, always darker than the surrounding bark, and obvious on most tree species. The collar is a swollen area at the base of a branch. This region between the branch and the trunk acts as a natural barrier to decay-causing organisms. The cut should be on a slight angle and in a down and outward direction from the tree as demonstrated in Figure 2.

A cut made straight down and close to the trunk is known as a “flush cut” and should be avoided. Flush cuts create a larger open wound that can develop decay of the branch attachment and over time lead to internal decay of the trunk.

Research has shown that wound dressings and other pruning agents do not prevent decay. When exposed to the sun, the protective coating often cracks, allowing moisture to enter and accumulate in pockets between the wood and the wound covering. This situation may be more inviting to wood rotting organisms than one with no wound cover. The use of wound paints and tars are not recommended as the tree has its own healing properties.

Broadleaf Evergreen Trees

Broadleaf evergreens, such as magnolias and hollies, usually require little to no pruning. In fact, most broadleaf evergreens develop a naturally symmetric growth habit when left alone. Pruning during the early life of the tree in order to balance the growth or to eliminate multiple trunks and/or multiple leader branches may be a consideration. Otherwise, routine annual pruning is not recommended.

Pruning Conifers (Needle-Type Evergreens)

Most upright-growing plants in this group, such as spruce, pine, cedar, and fir, have branches spaced evenly around the main trunk. They develop a symmetrical growth habit and become quite large at maturity. If planted in open areas and given plenty of room to grow, they require minimal pruning.

Removing approximately one-half of the new shoots while new growth is in the “candle stage” (small immature needles packed around the stem resembling a candle), will thicken the growth of pines and spruce. Avoid cutting back into the hardened older wood because new shoots will not grow, and the form of the plant will be compromised.

If upright and broad-spreading junipers outgrow their site, consider a form of reduction pruning. Reduction pruning using either thinning or heading back cuts to reduce plant size without destroying the natural shape. Only shear prune to keep a desire formal shapes like they do with Christmas trees.

Similar to pines and spruces, junipers do not generate new growth from old wood, so never severely prune more than one-half of the plant. The length of individual branches may be reduced by cutting them back to a lateral branch. This technique maintains a natural appearance while it decreases the size of the shrub.

Pruning Palms

Proper palm management only recommends the removal of fronds that have turned completely brown and have no green color remaining in the frond or petiole. Removal of fronds that have green coloring reduces their photosynthetic rate, which may have a negative impact on growth and development of the palm. Remove palm fronds by cutting them from the underside to avoid tearing the fibers of the palm’s stem. The terminal bud of the palm is where new fronds develop. If one damages the terminal bud, it may result in the death of the palm.

Para obtener la versión en español de esta hoja informativa, consulte HGIC 1003S, La Poda de Árboles.

Originally published 01/99