Help Trees Take Shape: Prune Properly
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Help Trees Take Shape: Prune Properly
CHAMPAIGN, Ill. -- In search of a strong structure and a desirable form…for your tree? If so, prune your trees when they are young. This will result in less need for corrective pruning as they mature. In fact, with a basic understanding of tree biology, homeowners can properly prune young trees, maintain tree health and structure, and enhance the aesthetic and economic values of their landscape, says Jim Skiera, Executive Director of the International Society of Arboriculture (ISA).
Why do people prune trees?
People commonly prune trees to remove dead branches, remove crowded or rubbing limbs, or to eliminate hazards. Trees also are pruned to increase light and air penetration to the inside of the tree's crown or to surrounding landscape. But in most cases, mature trees are pruned as a corrective or preventative measure. Since each cut has the potential to change the growth of the tree, no branch should be removed without a reason, warns Skiera.
"Urban environments are not 'natural' conditions for trees, so trees usually have to be modified in some way," Skiera explains. "But homeowners need to remember that heavy pruning can severely stress a tree. They need to exercise caution and a little common sense when they prune."
Removing foliage, the primary source of energy-producing sugar for trees, can reduce growth and stored energy reserves. Skiera says a good rule of thumb for pruning is to maintain at least half the foliage on branches in the lower two-thirds of a tree.
There are specific types of pruning that help trees stay healthy, safe, and
- Cleaning removes dead, dying, diseased, crowded, weakly-attached, and low-vigor branches from the crown of a tree.
- Thinning selectively removes branches to increase light penetration and air movement through the crown and reduces weight on heavy limbs to retain the tree's natural shape.
- Raising removes lower branches from a tree to clear space for buildings, vehicles, pedestrians, and views.
- Reduction trims the height or spread of a tree by pruning back the leaders and branch terminals to lateral branches that are large enough to assume the terminal roles (at least one-third the diameter of the cut stem). Compared to topping, this helps maintain the form and structural integrity of the tree.
When to prune
Most routine pruning to remove weak, diseased, or dead limbs can be done at any time of the year. But growth is maximized and wound closure is fastest if pruning occurs before the spring growth flush - when trees have just expended a great deal of energy to produce foliage and early shoot growth. Heavy pruning immediately after growth flush can stress the tree. Avoid pruning during active disease transmission periods. A few tree diseases, such as oak wilt, can be spread when pruning wounds allow spores to access a tree.
Proper pruning cuts
A pruning cut's location is critical to a tree's response in growth and wound closure. Pruning cuts should be made just outside the branch collar, which contains trunk or parent branch tissue that should not be damaged or removed. When removing a large limb, first reduce its weight to avoid tearing the bark by making an undercut about 12 to 18 inches from the limb's point of attachment. Then make a second cut from the top, directly above or a few inches further out on the limb.
How much to prune
The amount to remove depends on the tree size, species, and age, as well as pruning objectives. Younger trees can tolerate more pruning than mature trees. Skiera says: "A tree can recover faster from several small pruning wounds than from one large wound." Removing just one, large-diameter limb can create a wound that the tree may not be able to close. The older and larger the tree, the less energy it has to close wounds and ward off decay or insects.
Hiring an arborist
Pruning large trees can be dangerous. It usually involves working above the ground and using power equipment. Ensure your safety, and that of your trees, by hiring an ISA Certified Arborist. Find one in your area, along with more tree care information, at www.treesaregood.org.
The International Society of Arboriculture (ISA), headquartered in Champaign, IL, is a nonprofit organization supporting
tree care research around the world. As part of ISA's dedication to the care and
preservation of shade and ornamental trees, it offers the only internationally-recognized certification program in the industry. For more information, or to find a local ISA Certified Arborist, visit www.isa-arbor.com.