Pruning Mature Trees Is Best Left To Professionals

December 22, 1998

UNIVERSITY PARK, Pa. -- The key to pruning mature trees, according to a community forestry expert in Penn State's College of Agricultural Sciences, is remembering that older trees, much like aging people, are slower to recover from injury, illness or structural adjustments.

Mature trees are defined as trees that have reached a mature age or size for a species, according to Bill Elmendorf, instructor and urban and community forest program coordinator in the School of Forest Resources.

"Most homeowners can determine if a tree is mature by researching its size and age range," Elmendorf says. "If a tree can grow to 80 feet and your tree is 60 or 70 feet, it's a mature tree. If the species can live 100 years and your tree is 70 years old, it's mature."

Elmendorf emphasizes that mature landscape trees must be pruned carefully because haphazard or ill-considered pruning causes injury, decline or even death in a plant that has established its system for energy production, storage and use. Fruit trees, he warns, have very different pruning guidelines than other tree species.

"A tree gets its energy through its leaves by photosynthesis," Elmendorf explains. "A tree uses energy for growth and maintenance of living tissue, reproduction and resisting decay. In addition, some energy is stored for future use. Younger trees use most of their energy for growth, but older trees use most of their energy for maintaining live tissue, which means not as much energy is available for growth and defense against decay."

"If you remove too much green, the mature tree will respond by using its stored energy to promote new growth," Elmendorf adds. "You also create many wounds susceptible to decay, which the tree must defend against. With repeated or large injuries, the tree's energy generation and storage capability has been reduced, so the tree will use its stored energy again and again until the tree goes into a spiral of decline or death."

Elmendorf says mature trees should be pruned only if:

  • trees have crossed branches, weak crotches or defects
  • branches are dead, decayed, dying or hazardous
  • lower branches interfere with people or vehicles, or obscure visibility
  • branches are growing into buildings or utility wires
  • limbs are broken by storms
  • trees are too large and present a hazard to people and property

Elmendorf says homeowners should not try to prune mature trees in most cases. "Pruning should always be done by a qualified arborist who understands and uses current safety and pruning guidelines," he says.

Homeowners should be familiar with different types of pruning cuts to ensure proper tree care.

--Thinning Cut. This method removes a branch to its point of origin on the trunk, or shortens the length of a branch back to a side branch that is large enough to resume growth of the pruned limb. "On large trees, the standard is pruning back to a side branch that is one-third the diameter of the branch you are pruning," Elmendorf explains. "For example, if a limb is 10 inches in diameter, prune it back to a connecting branch that is at least 3 inches in diameter."

--Drop-Crotch Cut. Used on large branches more than 15 inches in diameter, this technique uses the same method as a thinning cut. "It's a large thinning cut used mostly for reducing a tree's size," Elmendorf says.

--Heading Cut. This cut should not be used unless the entire tree is being removed. The branch is trimmed back to a bud or to a very small branch that cannot assume the growth of the pruned branch.

--Stub Cut. This cut is made indiscriminately on a branch where no bud or adjoining branch exists. "This is a topping cut that should be used only when you are removing a tree," he says. "Topping is the ultimate in destructive pruning practices."

Cutting a branch correctly is another important element in pruning. Elmendorf recommends natural target pruning, a method in which the branch is cut to protect the branch collar -- above the area of swelling at the base of a branch. "Branches should never be cut flush to the trunk or left as a branch stub," he says. "Natural target pruning helps the tree form wound wood to heal a cut."

Elmendorf says homeowners should make sure they are pruning at the right time of year to ensure tree health. "Deciduous trees should never be pruned when they are growing new leaves in the spring or when they are losing leaves in the fall," Elmendorf says. "The best time to prune a tree is in winter, when they are dormant."

Elms and white oaks should not be pruned in the summer, because beetles carrying the pathogens for Dutch elm disease and oak wilt are active in the summer and are attracted to fresh pruning cuts. Dogwoods and flowering fruit trees should be pruned right after their flowers fade in late spring or early summer to protect the next year's flower buds.

Elmendorf lists other pruning do's and don'ts:

--Do keep pruning cuts as small as possible.

--Don't use tree wound dressing. "Dressing seals in moisture and decay spores and prevents wound wood from forming," Elmendorf says.

--Don't remove more than 25 percent of the tree's leaf area in any year.

--Do remove all dead wood first when pruning. "You may find you don't need to do any further pruning," Elmendorf says.

--Do step back and look at what you are doing when pruning. "Pruning cuts should be distributed equally," he says. "Don't cut all interior branches, or don't make all your cuts in the lower half of the tree."

--Don't attempt to climb a tree, use ropes to climb a tree or use a ladder to prune. "Only people trained in those methods have any business in a tree," he warns.

--Don't take a chainsaw into a tree or operate it above your head when pruning. "Homeowners should only prune using a hand pole saw while standing on the ground," he says. "There have been many horrific injuries to homeowners using chainsaws to prune."

--Do hire a qualified arborist to do any major pruning on a mature tree.

"The key to reducing pruning needs in a mature tree is to buy and plant a healthy tree with good structure," Elmendorf says. "Once the tree is planted properly, prune the young tree using hand shears so you can reduce pruning and the size of wounds in the tree's later years."

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EDITORS: For more information, contact Bill Elmendorf at 814-863-7941.

Contacts: John Wall jtw3@psu.edu 814-863-2719 814-865-1068 fax

Last Updated March 19, 2009