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HO-45

Pruning Landscape Trees

Original authors: M.L. Witt, R.E. McNiel, and W.M. Fountain
Contact: W.M. Fountain, Department of Horticulture

Flowering and shade trees in the landscape require periodic pruning to control size and shape, to correct undesirable growth, and to remove low-hanging or damaged branches.

The pruning tools for trees are the same as those required for ornamental shrubs:

Note: Do not use fine-toothed carpenters' saws. Hedge shears are of no use in pruning trees unless a formal hedge or screen is desired.

Figure 1. Tools used in pruning include (left to right) hedge shears, loppers, pruning saw, and hand pruners.

When to Prune

Flowering Trees

Ornamental trees that flower before June first should be pruned immediately after flowering. These include redbuds, smoke trees, magnolias, flowering and kousa dogwoods, hawthorns, crabapples, flowering cherries, peaches, pears, and plums.

Trees that flower after June first should be pruned in winter or spring before new growth begins. These include goldenrain trees, sourwoods, and other late-flowering trees.

Shade Trees

Trees restore themselves more rapidly if they are pruned in early spring before they leaf out. The framework is bare, and you can easily see which branches need to be removed. When pruning is done in early spring, the plants are soon in full leaf and actively photosynthesizing, thus providing food and energy required for closing or sealing wounds after pruning.

Some trees, such as birch, yellowwood, elm, pine, spruce, fir, and maple, will bleed excessively if pruned in the spring. Bleeding, or loss of sap, will not harm the tree, but may be unsightly or messy around the home. Bleeding may be reduced by pruning such trees when they are in full leaf (June).

What Trees to Prune and How to Do It

Making Cuts

There are methods for pruning trees to get the best results. Proper pruning involves removing dead, dying, or living branches without damaging or removing the branch collar. (See Fig. 2)

Figure 2. Notice the location of the bark ridge marking the branch collar.

Start at the top of the tree and work down. This makes it easier to shape the tree.

Figure 3. Stubs remaining after pruning die back and the decay often spreads to the interior of the tree.

Figure 4. The downward stroke is for stubbing the branch and removing excess weight. The final cutting stroke is at the branch collar, matching its angle, and leaving the collar intact.

Treating Cut Areas

Do not paint wounds. When cuts are made properly at the branch bark ridge, trees are able to compartmentalize, or set boundaries, at the injury (pruning) site. This process helps resist the spread of infection. Trees can resist the spread of microorganisms if they are fast and effective in setting the boundary defense system, but some are fast and others slow at this process.

No matter how efficiently or inefficiently the tree sets boundaries, wound dressings do not stop decay and actually increase the rate of decay. Therefore, it is not necessary to paint wounds once a cut is made. Rather, leave the tree to its own defenses.

Pruning Trees is an Annual Job

If minor pruning is done every year, the job is manageable and the plant remains healthy. A beautiful plant form is retained, and pruning cuts remain virtually unnoticed unless close inspection is made.

However, when plants are neglected over a period of years, major pruning considerably changes the plant's form. Furthermore, removing large amounts of wood at one time is detrimental to the plant's health.

Pruning Newly Planted Trees

Corrective pruning of a tree at the time of planting sometimes works for the tree's good. Dead, damaged, or misshapen branches can create problems later and therefore should be removed at planting time.

Prune newly planted trees to remove problem branches and to "shape up" the tree to a form typical of the species. Generally, entire branches should be removed, as shown in these "before" and "after" pruning shots of Stewartia pseudocamellia (see Figs. 5 and 6).

Figure 5. Before pruning.

Figure 6. After pruning.

Figure 7. Major scaffold branches should be spaced vertically at least 18 to 24 inches apart.

Pruning Young Established Trees

A regular pruning program begun while trees are young will prevent extensive repair work when they are older.

Figure 8. The sweet gum is a dominant leader tree.

Figure 9. An example of a modified leader tree is the honey locust.

Figure 10. Note this plant's tendency to develop two forks each time it forms a new set of branches. Keep the stronger branch, and remove the weaker (less desirably placed) one.

Figure 11. Branches growing much faster than the rest of this juniper need to be totally removed so the plant will resume its natural pyramid form again.

Figure 12. Dehorned trees are unsightly and prone to quick decline. Never leave stubs of branches in pruning.

Pruning Large Trees

Pruning requirements for large, mature trees are the same as those listed for younger plants. The major difference is size: working in large trees can be dangerous. When pruning is necessary, it is best to obtain the service of a certified arborist.

Figure 13. A southern magnolia suffering from extensive winter damage should be reshaped after the dead wood is removed.

Figure 14. Continuous rubbing provides easy access for diseases and insects.

Figure 15. Which limb do you remove? The smaller or less thrifty one.

Figure 16. The smaller branch was saved.

Figure 17. Water sprouts grow vertically from the branches and cause crowding in the middle of the plant. They should be removed as they appear.

Figure 18. Suckers growing near the base of the Katsura tree's trunk (above) may rob the plant of nutrients and water. Therefore, they should be removed.

Figure 19. To remove suckers, use a hand pruner close to the ground, removing the sucker as close to its origin as possible.

Figure 20. This picture shows the same Katsura tree with all suckers removed.

Pruning Multistemmed Trees

Multistemmed trees, such as the Washington hawthorn and saucer magnolia, present special problems. They usually become thick and matted in the center. To keep the multistemmed effect, the center should be kept open. Remember when pruning multistemmed trees that the stems compete with each other. The weaker member will be crowded out.

Figure 21. Multistemmed trees require annual pruning to prevent this type of cluttered, untrained growth habit.

Figure 22. Remove entire branches at soil level when pruning mutistemmed trees.

Figure 23. The multistemmed tree has been opened by the removal of excess branches. Old or unthrifty branches should be cut first; then, remove additional branches to reshape the plant into a desirable form.

Figure 24. Growth of extra branches is not uncommon when a tree is under stress from pruning or environmental conditions. This is a typical example of how latent buds will be forced into growth. These undesirable branches should be removed as they occur, definitely before their diameter interferes with the normal development of the branch to the left of the tree.

Figure 25. The same tree after pruning shows how the new branches can be taken out without harming the tree's basic structure.

Figure 26. Unusual growth forms can occur on plant material such as the upright branch in the center of this photo, which has looped around the branch above and adjacent to it. Though it gives an interesting form, it should be removed before it rubs open wounds or girdles another branch.

Figure 27 Pruning of roots is also necessary at times. These are two examples of girdling roots. Girdling roots can develop when roots are not spread out at planting time. As the trunk and roots grow in diameter, the encircling root chokes or strangles the tree since there is no way for it to loosen itself. The situation gets progressively worse, until the tree dies from lack of food and water transport in the phloem and xylem vessels.

Figure 28. Treat it by severing the root at the point of attachment. A wood chisel usually makes the job easier than using a pruning saw. Leave the root in place, since pulling it loose may expose open wounds caused by the rubbing of roots and trunk.

Figure 29. Trees, even when they are young, should have a flared base where the framework roots form off the trunk similar to the flared roots seen in this photo. When a trunk descends into the ground straight rather than with this type of flare, you should suspect girdling roots similar to the top photo.

Figure 30. When girdling roots are not corrected, the tree may simply snap at soil level. This photo shows why a large tree toppled for seemingly no good reason. Close examination of the remains showed this severe case of girdling roots.

Figure 31. Not all Callery pears are noted for narrow branching angles. The cultivar 'Aristocrat' is noted for the potential of horizontal branching, as shown here.

Figure 32. Many young trees are not pruned correctly in the nursery and are sold with this quantity and arrangement of branches. If left like this, the plant will develop problems as the branches increase in diameter.

Figure 33. In time, the tree will grow to be like this—CROWDED!

Figure 34. When there has been too much branch competition, the tree will lose branches in high winds.

Figure 35. This Callery pear did not develop horizontal branching and has the potential to develop structural problems. Training and pruning at a young age would have avoided this problem.

Quick Rules of Pruning Flowering Trees and Shrubs

As a rule of thumb, if it flowers before June 1st, prune it after flowering. If it flowers after June 1st, prune it before flower buds are visible.

Spring Flowering

Aesculus: (horse chestnut, buckeye)
Amelanchier: (serviceberry, sarvistree, shadbush)
Carpinus: (hornbeam)
Carya: (pecan, hickory)
Castanea: (chestnut)
Cercis: (redbud)
Chionanthus: (fringetree)
Cladrastis: (yellowwood)
Cornus: (dogwood)
Corylus: (filbert)
Crataegus: (hawthorn)
Halesia: (silverbell)
Hamamelis: (witchhazel)
Ilex: (holly)
Magnolia: (magnolia)
Malus: (crabapple, apple)
Prunus: (cherry, plum)
Pyrus: (pear)

Summer Flowering

Albizzia: (mimosa)
Cotinus: (smoke tree)
Koelreuteria: (goldenrain tree)
Sophora: (Japanese pagodatree)
Oxydendrum arboreum: (sourwood)


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