Garden Tips: Avoid hazardous trees

You probably have heard about the many trees that came down across our state in the wind storm recently, but you may not have heard about a tree in Spokane that snapped off and speared a house. It entered the roof, went through the crib of a 6-week-old baby, and stopped only when it reached the basement floor. Thankfully, the baby was with his mother, who was in the kitchen fixing dinner, and the rest of the family was safe too. This hazardous tree story hit home for me because that baby is my grandson.

I have talked often about not topping trees, but this story emphasizes why it is important to prune properly and to periodically assess large trees for potential hazards.

A tree is considered hazardous when all or part of it could fail and damage a target, such as a building, vehicle or a person. Common failures are the breaking off of a tree limb, a tree splitting a part or a tree uprooting and falling over.

Some reasons for a tree failure include wood decay from past topping; other bad pruning cuts or injuries to the bark and trunk; a lopsided crown; competing central leaders or main branches that are weakly attached at a less than 45 degree angle; the severing within the drip line of more than 50 percent of a tree’s root system; and the development of significant girdling roots at the base of a tree.

The failure of a small tree is usually insignificant, but the failure of a large tree can be catastrophic. When I first moved to this area in 1980, we didn’t have many large mature trees in our home landscapes. Now there are many more. This is good, but it has also increased our potential for hazardous trees.

If you have a larger and older tree, check for any signs of potential failure in shade trees and then consult an International Society of Arboriculture certified arborist if there might be a problem.

Signs of potential tree failure:

• trees that have been topped in the past
• a tree that is leaning
• a tree with multiple trunks or with competing leaders
• trees with lopsided crowns
• trees with dead or broken branches
• trees with dead areas of trunk or signs of wood rot

If you have a smaller tree that will grow into a big one, also consider having an arborist check for any corrective pruning that is needed to avoid future problems. It is better and less expensive to take care of these problems when the tree is young.

It is possible that a consultation with an arborist before last week’s extraordinary wind event might have avoided the damage to my family’s home, the deaths of several people and the property of many others, but there is no way to know for sure. Hindsight is always better than foresight.

This story was originally published November 28, 2015 at 11:32 PM with the headline "Garden Tips: Avoid hazardous trees."