Q. I have a wisteria that is climbing up and around and around a large fir tree. Will it damage my fir tree? Pat Stougard – Vashon Island, WA
A. Wisteria are considered a problem when growing over or on woody trees and shrubs. They can strangle smaller specimens and if they reach to top of the tree or shrub will also kill by shading. They are not killing parasitically the way mistletoe does – by tapping right into the tree and extracting nutrients. Instead they wrap around and try to outgrow the tree or shrub to get to the best light. Now your large fir tree may be so big it would never reach to top to completely shade it out but it will kill off lower branches of the tree as it climbs. In addition it adds more drag force to the tree when we have windstorms. This increases the chances that your tree will succumb to a blow down. It is usually best to train wisteria to a man made structure and keep it managed.