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Questions about Trees and Utilities

This article answers five common questions about trees and utilities, and how conflicts between trees and wires can be resolved. It includes tables listing low-growing trees compatible under utility wires and medium-size trees compatible near utility wires.

Why is the utility company "butchering" our trees?

Pruning trees along overhead utility lines reduces electrical interruptions, provides safe conditions for the public, and protects power company employees. Most interruptions during storms are caused by trees. One type of service interruption, called a momentary interruption, is annoying to the customer because it lasts just long enough to affect sensitive electronic equipment such as clocks, VCRs, and computers. A second type, called a sustained interruption, results in a complete loss of power. Sustained outages occur mainly during severe weather, and may cause serious damage to electric facilities.

The utility company hires contractors whose trained tree workers clear vegetation back to distances that are consistent with safe and reliable electric service. Clearances between trees and wires vary according to different voltages of primary and secondary conductors. Also, pruning practices may differ between urban and rural areas. Most utilities use an arboriculturally correct method called directional pruning, instead of topping and shearing. Directional pruning directs subsequent growth away from wires and leaves no stubs. Even a properly pruned tree growing near wires may have a disfigured appearance.

Can't wires be buried underground, to get them out of our trees?

In new developments, electrical conductors usually are placed underground. But to relocate existing wires from poles to an underground installation would be prohibitively expensive. Besides the expense to the utility company, property owners would have to dig up their yards and relocate the electrical entrance to each building at a cost of several thousand dollars. Moreover, the trenching would tear up tree roots, which could injure or kill the trees. Future maintenance of underground utilities can be disruptive to established landscape plants, and repairs would result in longer outages.

How can the conflict between trees and wires be resolved?

The best long-range solution is to replace incompatible trees (those that interfere with wires) with new trees that will not grow into wires. Trees can be replaced all at once, or one at a time as trees become overmature and unhealthy. The choice between sudden or gradual replacement depends on various considerations, including the type of landscape desired in a neighborhood. A formal design with uniformly spaced trees of the same kind and size requires planting all trees at the same time. An informal planting design can be implemented over several years, with less disruption in the appearance of the neighborhood.

The design concept of trees that are compatible with utility lines has been called "the right tree in the right place." The right tree for planting under utility wires is a species that will not be taller than 20 to 30 feet at maturity (Table 1). Medium-size trees, up to 45 feet at maturity (Table 2), can be planted near utility lines if they are offset at least 15 feet from the nearest wire. Adequate space for root growth also is an important consideration when deciding tree size and placement. Low-growing trees are most appropriate if the space for roots between the curb and the sidewalk is less than 4 feet wide. If pedestrians and vehicles pass by the planting site, the variety selected should have ascending branches and a single trunk that can be pruned up for clearance.

Table 1. Low-growing trees compatible under utility wires; mature sizes in urban situations.
Common Name Scientific Name Mature
Height
Mature
Width
choke cherry, Shubert Prunus virginiana Shubert 20-30 15-20
crabapple varieties:
Adams, centurion, harvest Gold, madonna, Prairifire, Prof. sprenger, red Barron, red Jewel, sentinel, snowdrift, spring snow, sugar Tyme, Zumi, or redbud
Malus varieties: 16-30
*depends on variety
8-30
*depends on variety
dogwood, kousa and hybrids:
celestial, constellation, Julian, milky Way, stardust, steeple, stellar Pink
Cornus kousa and varieties: 20-30 20-30
hawthorn varieties:
crimson cloud, inermis, ohio Pioneer, phaenopyrum, Vaughn, Winter King
Crataegus varieties: 15-30
*depends on variety
12-35
*depends on variety
Japanese tree lilac varieties:
Ivory Silk, Regent, Summer Snow
Syringa reticulata varieties: 20-30 15-25
magnolia, Galaxy Magnolia Galaxy 20-30 10-15
magnolia, Star Magnolia stellata 10-20 10-15
maple, Amur Acer ginnala 15-20 15-20
maple, paperback Acer griseum 25-35 15-20
maple, Tatarian Acer tataricum 15-25 15-25
maple, trident Acer buergeranum 20-30 20-30
serviceberry varieties:
Autumn Brilliance, cumulus, majestic, Princess diana, robin hill, Tradition
Amelanchier varieties: 20-30
*depends on variety
12-20
*depends on variety
Table 2. Medium-size trees compatible near utility wires, offset at least 15 feet; mature sizes in urban situations.
Common Name Scientific Name Mature Height Mature Width
birch, Heritage Betula nigra heritage 40-50 30-40
cherry varieties:
Accolade, Kwanzan, Okame, Rosy Cloud, Sargent columnar
Prunus varieties: 25-40
*depends on variety
12-35
*depends on variety
corktree, Amur, varieties:
Macho, Shademaster
Phellodendron amurense varieties: 35-45 30-40
goldenrain tree Koelreuteria paniculata 25-40 25-40
honeylocust, Imperial Gleditsia triacanthos Imperial 30-40 35-45
hophornbeam, American Ostrya virginiana 30-40 20-30
hornbeam, American Carpinus caroliniana 20-35 20-35
hornbeam, fastigate Carpinus betulus fastigiata 40-50 30-40
horsechestnut, red Aesculus x carnea 35-50 30-45
magnolia, Merrill Magnolia Merrill 25-40 25-40
maple, Crimson King Acer platanoides Crimson King 40-50 35-45
maple, Olmstead Acer platanoides Olmsted 35-45 20-25
maple, Norwegian Sunset Acer truncatum Norwegian Sunset 35-45 25-35
maple, Pacific Sunset Acer truncatum Pacific Sunset 30-40 25-35
maple, Queen Elizabeth Acer truncatum Queen Elizabeth 30-40 25-35
pagoda tree varieties:
Halka, Regent, Princeton Upright
Sophora japonica varieties: 40-50 25-40
pear, callery, varieties:
Aristocrat, Autumn Blaze, Capital, Chanticleer, Cleveland Pride, Cleveland Select, Valiant, Whitehouse
Pyrus calleryana varieties: 35-45
*depends on variety
12-35
*depends on variety
yellowwood Cladrastis kentukea 35-50 40-55

Can't we have any large trees?

Yes, many residential neighborhoods and other locations can and should accommodate properly placed large trees. Utility lines usually are along just one side of a street; large trees can grow on the opposite side if there is ample space for the roots and branches. Other open spaces away from the street also can accommodate large trees, though they should be planted far enough away from buildings. In fact, a diverse mixture of tree sizes and species tends to be healthier, with fewer disease or insect problems. Large trees are recommended where space permits, as they contribute most to cleaner air, moderating temperatures, and reducing storm water runoff.

Who can answer my other questions?

Contact your local utility, Penn State Cooperative Extension office, or Pennsylvania District Forestry office.

Produced by Henry D. Gerhold, professor emeritus of forest resources, and William F. Elmendorf, associate professor of urban and community forestry.

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Title

Questions about Trees and Utilities

Series

Urban and Community Forestry in Pennsylvania 7

Code

UH100

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Contact Information

William Elmendorf
  • Associate Professor
Email:
Phone: 814-863-7941