Purpose of the Handbook

Large trees growing under or close to power lines often create severe problems. Branches which break during wind or ice storms can knock down the lines creating dangerous situations and disrupting power service. Pruning to keep branches from rubbing against the lines is a continuous problem and cost to utility companies. It may also be difficult to prune trees in a fashion that does not create an unnatural form and an unsightly appearance. The best answer to this problem is to choose smaller trees and shrubs for planting both under and next to power lines. This handbook was prepared to describe and illustrate some possible plants to use in landscaping under and near power lines. Large trees are also described to make the book a more complete listing of woody landscape plants.

Interpretation of Information

Trees and shrubs are living organisms that respond differently under varying site conditions and maintenance practices. Thus, size and appearance can vary for the same plant in different situations. The following definitions describe how to interpret statements made in this handbook.

Height and Width: Size given is the average size that plants listed would reach at maturity when growing under average conditions in the upper midwest. Old specimens, or plants growing under very favorable conditions, or those receiving excellent care may be somewhat larger.

Limitations: Only very serious insect or disease problems are listed here. There are many insects that frequently feed on plants that may cause foliage to appear injured but don't cause a threat to the health of the plant. Many leaf spots and other foliage diseases also cause the foliage to appear unsightly on close inspection but don't pose a threat to the plant and are not very noticeable from a distance.

Shade tolerance: Plants grown in shade are usually less dense in habit, grow taller and are more leggy. In addition, these plants generally have fewer flowers. They tend to have more limited root systems which make them more susceptible to periods of drought. Many plants can tolerate some shade and still survive but don't have an acceptable landscape quality when grown under those conditions. Thus it is often difficult to characterize a plant's tolerance to shade. In this handbook, we list as shade tolerant only plants that will have a fairly good plant quality when grown in shade.

Hardiness Zone: The hardiness zone listed for each plant follows the U.S.D.A. hardiness zone map which is based on minimum winter temperatures. Hardiness zones can be further divided into (a) and (b) with (a) being the colder half of the zone. The capability of plants to withstand winter cold is often difficult to characterize since many factors can influence a plant's ability to acclimate to cold temperatures. Plants not only need to be able to withstand the coldest winter temperatures, but they must harden soon enough to tolerate early severe cold temperatures. They must also be able to retain hardiness through periods of warm weather in winter or early spring that might be followed by more low temperatures. General health and vigor of the plant can influence its ability to acclimate. Microclimate can also greatly affect the temperature compared to that of the general area. Thus a marginally hardy plant grown in a favorable site with good growing conditions and provided good maintenance can survive. The hardiness zone listed is the coldest zone that the plant can tolerate when grown under average growing conditions.

Color code: To help in readily identifying plants that can safely be grown underneath power lines, a color code appears on the right hand margin of each plant description sheet.

Green: indicates plants that usually do not exceed 25 feet in height and can readily
be planted underneath power lines.
Yellow: indicates medium size trees that grow to heights of 25-40 feet.
These should not be used under most power lines.
Red: indicates tall trees that grow to heights exceeding 40 feet in height.
These should never be planted under power lines.

Handbook Reviewers

We wish to thank Dr. Edward Hasselkus, Department of Horticulture, University of Wisconsin, Dr. Dale Herman, Department of Horticulture and Forestry, North Dakato State University, Dr. Bert Swanson and Dr. Jim Calkins, Department of Horticultural Science, University of Minnesota for their critique of the handbook and for their excellent suggestions which helped in improving the accuracy and detail of the information presented.

Photo Credits

Photographs used in the handbook were provided by a number of individuals. Photo credits given at the bottom of the front page of each factsheet relate to those photos on the back of the particular sheet. They relate to the photos from left (1) to right, top (2) to bottom (3). Photos taken by current or former staff members of the Minnesota Landscape Arboretum and the Department of Horticultural Science, University of Minnesota are indicated by MLA. Photographs were also contributed by staff of Bailey Nurseries, Inc., St. Paul, MN; staff of Dakota County Technical College, Rosemount, MN (designated by DCTC); Laverne Dunsmore, Otten Bros. Nursery & Landscaping, Inc., Long Lake, MN; Dr. Edward Hasselkus, University of Wisconsin, Madison, WI; Keith Warren, J. Frank Schmidt & Son Co., Boring Oregon; and the Minnesota Nursery and Landscape Association (MNLA).