Choosing Trees To Plant Near Streets

On Sunday, Peter Shaw, professor of horticulture at Spokane Community College, will host a free tour of some of the not-so-common trees and shrubs at the Finch Arboretum. One of the highlights of the tour will be the new street tree exhibit.

This outstanding display, though young, introduces us to many tree species that are excellent candidates for planting alongside streets, sidewalks and under power lines. In most cases these trees are shorter and narrower than their larger relatives. And because they are smaller, their root systems don’t have to be quite as aggressive.

So why is it important for us to become familiar with these smaller trees? From years of overcrowding, poor pruning practices, moisture stress, pollution, disease, insects and age, many of our street trees are in a state of rapid decline. The day is coming when many will need to be replaced.

Large, older trees are also creating hazards. As their roots seek out moisture and mature into large swollen underground limbs, sidewalks are buckling. Cracked, heaving concrete creates a very unsafe path for pedestrians. Of course, we can hardly blame the tree. When most of these classic trees were planted, there were no sidewalks or streets to contend with. But today, there are sidewalks and homeowners bear the responsibility of maintaining them. And often, this can be a very costly undertaking.

While the roots of mature trees are causing one dilemma, their tops may be causing yet another when they grow into power lines. No one wins in the power line-vs.-tree dilemma - including the power company. Tree limbs whipping against lines cause power outages and fires. Power companies often have to severely prune the trees to prevent these major problems. Though they make healthy pruning cuts the trees often wind up looking dog-eared and downright ugly. But let’s face it, the power companies have NO choice in this matter. There are no alternatives.

Regulations require a 10-foot clearing below the primary lines (the top lines running from the poles). This 10-foot distance includes the neutral and secondary wires (the next set of wires running below the primary lines). A 10-foot clearing must also be maintained along the sides of the primary lines and a two- to three-foot clearing from the secondary lines. A 15-foot clearing is maintained above the primary line.

Sometimes the trees were there before the power lines and sometimes the power lines were there before the trees. In either case the beauty of the tree must be compromised for our safety. We see these misshapen old trees and we are disgusted by their appearance; yet, potentially huge trees are planted under power lines each year. By visiting the arboretum or, better yet, attending the tour, we can become acquainted with 34 outstanding “street trees.” Here’s a sampling of what you will see:

Karpick red maple (Acer rubrum “Karpick”): Height: 30 feet. Spread: 10 feet. This upright maple turns yellow to brilliant red in the fall. It thoroughly enjoys wet areas.

Katsura tree (Cercidiphyllum japonicum): Height: 35 feet. Spread: 20 feet. This slow-growing tree has a light, airy branch and leaf pattern. Leaves turn brilliant red or yellow in the fall. It does require special protection from hot sun and dry winds.

Queen Elizabeth hedge maple (Acer campestre “Queen Elizabeth”): Height: 35 feet. Spread: 30 feet. This is the best little tree. It seems to adapt to anything - compacted soil, heat, cold, sun or shade. No disease or insects seem to bother it. Fall color is yellow.

Goldenrain tree (Koelreuteria paniculata): Height: 35 feet. Spread: 35 feet. Obviously this is a round tree. This lovely specimen is a showstopper with its long, 8- to 14-inch flower clusters. It can tolerate cold, heat, drought and wind.

True shade honeylocust (Gleditsia triacanthos “True Shade”): Height: 40 feet. Spread: 35 feet. This fast grower has a broad, round crown with fine, textured leaves that yellow in the fall. It is an excellent specimen for a light, airy look.

Street trees aren’t only for the street. Because of their size, they make excellent trees for small gardens and privacy screens. If you would like to know more about these less commonly used tree species, join Peter on Sunday for a slide show at 1 p.m.; the tour follows at 2 at the arboretum.