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How to Prune a Tree or Shrub

How and When to prune a Live Oak.

Pruning is one of the most important cultural practices for maintaining woody plants, including ornamental trees and shrubs, fruits and nuts. You could train or direct the growth of plants into a particular form or a specified space, like a formal hedge, or prune mature plants to control size and shape. For fruiting plants, pruning plays an important role in improving overall fruit quality, primarily by increasing light penetration into the tree. Proper pruning requires a basic understanding of how plants respond to various pruning cuts. The principles and guidelines in this publication will help you master common pruning techniques.

Shoot Growth and Apical Dominance 

Figure 1. Terminal bud.

Figure 1a. Close-up of a node.

You can partly determine the characteristic shape and size of a woody plant and its response to pruning by the plant's natural pattern of shoot growth. When a seed germinates and grows, only one growing point exists, the apex or terminal bud (Fig. 1). When a terminal bud begins growing after being dormant, it leaves a bud scale scar on the branch, which you can use to determine the age of a limb or tree by counting. Nodes (spot where leaves grow) form as the shoot grows (Fig. 1a). One-three lateral buds are produced at each node. Growth of lateral buds is directed by the terminal bud, which produces the hormone auxin. Auxin moves down the shoot from the shoot apex and inhibits the growth and development of lateral buds (Fig. 2). This phenomenon is called apical dominance.

The intensity of apical dominance varies as some plants suppress the growth of their lateral buds until the second growing season and others develop lateral shoots and terminal buds during the first growing season. Apical dominance influences the number of shoot-forming lateral buds, the length of lateral shoots formed, and the angle the shoots grow from the main limb.

Figure 2. Apical dominance and its effects.

Figure 3. Limb orientation affects apical dominance.

The orientation of a limb or shoot along the main branch influences growth by its effect on apical dominance (Fig. 3). Because auxin moves down the shoot, apical dominance is strongest in upright shoots or limbs. In vertical limbs, vigorous shoot growth occurs near the terminal bud with lateral shoots becoming more sparse with increasing distance from the apex. Orientation of lateral branches at 45 to 60 angles from the vertical or main shoot reduces the vigor of shoot growth near the apex and increases the number and length of laterals along the limb further from the apex. On horizontal limbs, apical dominance is totally lost. Without apical dominance to control their growth, lateral buds on the upper side of horizontal limbs develop into vigorous, upright shoots, called water sprouts. As they develop, water sprouts show very strong apical dominance. Water sprouts are a common problem on the upper surface of flat limbs in fruit trees and are removed by pruning.

General Responses to Pruning

Pruning is an invigorating process (Fig. 4). By removing the apex, pruning temporarily destroys apical dominance and stimulates the growth of lateral buds into shoots.

Figure 4. Pruning stimulates lateral shoot growth close to the cut.

Pruning also reduces the size of the above-ground portion of the plant in relation to the root system (Fig. 5). As a result, the undisturbed root system services a smaller number of shoots and buds. The relative uptake of water and nutrients by the remaining shoots and buds increases, and growth occurs. Generally, the more severe the pruning the greater the regrowth, as the plant is growing in an attempt to restore a balance between the top and roots.

Pruning generally stimulates regrowth near the cut (Fig. 6). Vigorous shoot growth will usually happen 6 to 8 inches near pruning cut. This is particularly true for vertical limbs that have been pruned (Fig. 6a). However, regrowth on limbs having a 45 to 60 angle from the vertical will develop farther away from the cut (Fig. 6b). Pruning can also stimulate growth of lateral shoots by letting more light reach the canopy of the plant.

Pruning a young plant will stimulate shoot growth and delay the development of flowers and fruit. The length of the delay depends on the species pruned and the severity of the pruning.

Types of Pruning Cuts

There are two types of pruning cuts, heading and thinning (Fig. 7). Heading removes the terminal portion of shoots or limbs (Fig. 7). By removing apical dominance, heading stimulates growth near the cut. It also is the most invigorating type of pruning cut, resulting in thick compact growth and a loss of natural form, as in the case of a formally pruned hedge. Sometimes ornamental shrubs along a foundation overgrow their planting space and are rejuvenated by heading to within 12 inches of ground level. Many broadleaf shrubs such as burford holly, ligustrum, abelia and crape myrtle tolerate this type of pruning. Other types of heading are topping, dehorning, hedging and clipping.

Figure 7. Heading removes a part of a shoot or limb.

Figure 7a. Thinning removes the entire shoot or limb.

Thinning removes an entire shoot or limb to its point of origin from the main branch or lateral (Fig. 7a). Some shoot tips are left undistributed, so apical dominance is maintained. New growth occurs at the undisturbed shoot tips while lateral bud development and growth is suppressed. Thinning is generally the least invigorating type of pruning cut and provides a more natural growth form of plants. Thinning cuts are used to shorten limbs, improve light penetration, and to direct the growth of shoots or limbs.

Drop-crotching, a form of thinning used to reduce the size of large trees, involves the removal of a main branch by cutting it back to a large, lateral branch (Fig. 8a). The cut through the main branch is made parallel to the angle of the remaining lateral. When removing large tree limbs, a series of three cuts are recommended in order to avoid tearing the bark along the main truck and severely wounding the tree (Fig. 8b). One undesirable form of thinning is the bench cut, where a vigorous upright limb is thinned to horizontal limb.

Figure 8. Types of thinning cuts: (a) drop crotching and (b) limb removal.

Water sprouts often result from the "bench" area because of the absence of apical dominance in the horizontal limb and often results in an unwanted umbrella-shaped plant. The correct method is to make the thinning cuts to limbs that are similar in angle to the limb being removed and not greater than 45 to 60 from vertical. Shoots or limbs having narrow-angled crotches are weaker than those having wide crotch angles. The bark of the adjoining branches becomes tightly compressed, preventing normal wood development. Winter ice trapped down in crotches often causes narrow-angled branches to split.

Healing Response to Pruning

Healing follows pruning or wounding. It starts in the cambium, a thin layer of cells between the wood and bark. Two areas of the cambium, the bark ridge at the junction of two limbs and the branch collar, a ring of slightly raised tissue where the lateral branch joins the main limb, close off the wound between the plant and the pruning cut. For fastest healing, prune close to the main branch without injuring the bark ridge or branch collar areas. Leaving a stub will slow healing and invite decay. Wound dressings or pruning paint are cosmetic and do little to promote healing of the pruned area.

Time for Pruning

Prune After Flowering

Prune Before Spring Growth Begins

Azalea
Beautybush
Bigleaf Hydrangea
Bradford Pear
Bridalwreath Spirea
Clematis
Climbing Roses
Crabapple
Deutzia
Dogwood
Doublefile Vibernum
Flowering Almond
Flowering Cherry
Flowering Quince
Forsythia
Japanese Kerria
Japanese Pieris
Lilac
Mockorange
Oakleaf Hydrangea
Pearlbush
Pyracantha
Redbud
Saucer Magnolia
Star Magnolia
Shrub Honeysuckle
Thunberg Spirea
Vanhoutte Spirea
Weigelia
Winter Daphne
Wisteria
Witchhazel

Beautyberry
Camellia
Goldenrain Tree
Chaste Tree (Vitex)
Cranberrybush Viburnum
Crapemyrtle
Floribunda Roses
Fragrant Tea Olive
Gloss Abelia
Grandiflora Roses
Japanese Barberry
Japanese Spirea
Mimosa
Nandina
Rose-of-Sharon (Althea)
Sourwood
Anthony Waterer Spirea
Sweetshrub

Time of pruning varies with plant species. Prune at times that best complement the growth characteristics, flowering, and other objectives you desire.

Many woody ornamentals are pruned according to their date of flowering. Pruning spring-flowering shrubs during the dormant season will remove flower buds formed in the fall. Summer-flowering plants generally are pruned during the dormant winter season. If plants are not grown for their flowers, the best time for pruning is during the dormant winter season before new growth begins in the spring. Avoid heavy pruning during the late summer and fall because growth may occur and make the plants more susceptible to cold injury.

Some plants bleed heavily after pruning. Bleeding is unsightly but not usually harmful. Trees subject to bleeding should be pruned in the late spring or early summer when leaves are on the tree. Actively growing leaves tend to reduce the amount of bleeding from pruning cuts and allow the cuts to heal more quickly.

Summary

Pruning is an invaluable tool for developing and maintaining woody plants. Key points concerning the use of pruning in woody plants are:

  • Pruning stimulates growth in proportion to pruning severity. Light annual pruning is better than periodical severe pruning.
  • The two basic types of pruning cuts are heading and thinning. Thinning cuts are the least invigorating type of cut and are the most effective pruning cut for maintaining woody plants in their natural form.
  • Pruning, particularly heading cuts, stimulates growth very close to the pruning cut. Heading cuts, such as topping, dehorning and hedging, often are misused and destroy the natural shape of plants because they stimulate growth near pruning cuts.
  • Bench cuts, pruning upright limbs back to flat limbs, result in vigorous growth and weak limbs. Thin out limbs leaving those oriented at a 45 to 60 angle from vertical.
  • Pruning time should be dictated by requirements or characteristics of the plant such as flowering date and susceptibility to cold weather.
  • Wounds heal fastest when pruning doesn't disturb important areas of cambium such as the bark ridge and branch collar. Wound dressing is cosmetic and does not promote healing.
  • All too often, improper pruning techniques seriously damage or kill woody plants. If you wish to have woody plants properly maintained, personally supervise or conduct the pruning operation.

 

Acknowledgment is made to Dr. Stephen C. Myers for developing the original manuscript for this publication.

Bulletin 949/Revised April 1999

The University of Georgia and Ft. Valley State University, the U.S. Department of Agriculture and counties of the state cooperating. The Cooperative Extension Service, the University of Georgia College of Agricultural and Environmental Sciences offers educational programs, assistance and materials to all people without regard to race, color, national origin, age, sex or disability.

An Equal Opportunity Employer/Affirmative Action Organization Committed to a Diverse Work Force

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, The University of Georgia College of Agricultural and Environmental Sciences and the U.S. Department of Agriculture cooperating.

Gale A. Buchanan, Dean and Director