University of Vermont Extension 
Department of Plant and Soil Science

Anytime News Article

POWER LINES AND TREES

 Dr. Leonard Perry, Extension Professor
University of Vermont
 
 
Every summer during thunderstorms, and every winter during snowstorms, I thank my power company for clearing the rights of ways near their power lines to prevent service disruptions.  Proper care and pruning of trees on your property, as well as planting appropriate species in the beginning, can keep you and your property safe and with fewer power outages.
 
The most important point to remember if trees are already growing into power lines, is to not prune them yourself.  Such lines, especially the main ones feeding each home, are often not insulated.  Touching or even getting close to them could result in death.  Cutting branches that, when falling, could touch live lines should be avoided as well, as these could cause short circuits or fluctuations that damage electronics.  Alert your power company to such situations and either let them do the pruning or recommend qualified arborists.

If your trees are reaching towards the power lines, but not close yet, they should be pruned if they’ll eventually cause problems.  Spring, as growth is resuming, is the best time for such corrective pruning.  Of course you’ll need to know what the trees are and how tall they’ll get when grown.  Your local nursery can usually help if you aren’t sure.  Some trees may be short, or fully grown already, and never cause problems.  There is no need to prune these, unless for other reasons such as broken limbs.

When pruning trees under power lines, don’t shear as you might a hedge, or “top” horizontally.  These result in many smaller shoots that are weak and can break in storms or wind, lead to rot organisms entering, and weaken the tree overall.  If you employ a tree service, make sure they wont use this outdated practice.

Two better practices for pruning trees near power lines are the V-shaped and sidetrim methods.  In the former, used for trees directly under power lines, branches are removed from the center.  Side branches then grow up in a V-shape on either side of and away from the power lines.  In the latter, used for trees growing alongside power lines, branches are removed only from the side that might interfere with the lines. For either method, prune branches back to a side limb or to where they come from the trunk, to avoid sprouting of many weak side shoots.

If, by pruning trees as above, they are quite unsightly, it may be best to remove them all together.  Also remove fast growing trees, such as willows, that will need frequent pruning.  Old trees, or those that are weak, should be removed as well.  Structurally weak trees may have lots of rotten limbs waiting to fall, uneven shapes, and weak branch angles in narrow V patterns from the trunk.  

Of course the best practice is to not grow trees near power lines if none are currently present.  If trees are desired, often for screening or aesthetics, then plant low-growing ones.  They should be under 25 feet tall at maturity if they’ll be within 15 feet of power lines (as measured along the ground).  Those trees growing over 25 to 50 feet tall should be planted at least 30 feet from power lines.  Those growing over 50 feet tall should be planted at least 40 feet away.
 
Don’t plant under the smaller service lines from the pole to your home, as these are often lower than the main power lines. Nor should you plant vines that will climb up power poles, or support wires.  Utilities often recommend planting lower shrubs near poles, but not within about 10 feet.  If you want to screen unsightly poles and wires, this is best done by plants nearer to where they will be viewed, such as a porch or windows.  Just make sure and allow plenty of room for growth if planted near buildings, walks, or other structures.

There are a several good small trees or large shrubs to choose from for northern landscapes.   Crabapples are one of the most common small trees, attractive with spring flowers and fall fruits, growing 12 to 25 feet high depending on cultivar (cultivated varieties).  Make sure to look for disease-resistant cultivars, and don’t plant if the fruits will be a nuisance if dropping into lawns or onto sidewalks.

Japanese tree lilac (Syringa reticulata) is another small tree 15 to 20 feet high and 10 to 15 feet wide, having attractive bark and creamy white flowers in June.  American hornbeam (Carpinus caroliniana) reaches about 25 feet tall and a bit less wide, with attractive bark, spring flowers, and fall color.  Hawthorns are often recommended, getting 15 to 20 feet high and 10 to 15 feet wide, depending on species.  Make sure to get ones without lethal thorns.  Hedge maples (Acer campestre) are dark green in summer and gold in fall, but as they may reach slightly above 25 feet high and wide they may need some pruning. 

Ornamental plums and cherries generally reach 15 to 20 feet high and 10 to 15 feet wide, with very beautiful spring flowers.  Just make sure to buy ones hardy for your area.  Purpleleaf sandcherry (Prunus x cistena) only gets about 8 feet high and slightly less wide, with white spring flowers and reddish purple leaves. Showy or European mountainash (Sorbus) have attractive white flowers in June on trees 20 to 25 feet high, with bright orange or red fruit in fall.  Unfortunately, these may be short-lived due to insects and diseases.

Large shrubs might be used instead of small trees, just make sure they have room to spread if needed.  The native serviceberry (Amelanchier) has attractive gray bark on multiple stems to 25 feet tall and 10 to 15 feet wide, with white flowers in May and fruit (edible by birds and humans) later in summer. The Siberian peashrub (Caragana arborescens) is, as its name suggests, quite hardy.  Yellow early summer flowers appear on this shrub reaching 10 to 15 feet high and 5 to 8 feet wide.  Lilacs reach 10 to 15 feet tall and wide, with a range of flower colors most are familiar with in spring.

Saucer or star magnolias are large shrubs with a rounded habit, generally 8 to 12 feet high and wide, with generally white or pink flowers in early spring.  Native viburnums have nice white flowers in summer, followed by attractive fruits good for wildlife.  Depending on species they get 6 to 12 feet high and similarly wide.  Make sure to choose viburnums that are resistant to the viburnum leaf beetle such as the doublefile, leatherleaf, or Siebold. 

Whether trees or shrubs, if near roadsides in the north, make sure they are salt tolerant, one of the best being the Japanese tree lilac.  Avoid trees that you may find sometimes recommended but that may be invasive, such as amur and tatarian maples, honeysuckle shrubs, or Russian olive.  Check your local nursery for more choices of plants that are power-line friendly.
 

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