Saturday, July 27, 2013 —
Visualize a 17th-century English country home with its manicured gardens and nearby outbuildings, and you'll likely imagine brick walls covered so completely in ivy that only the windows and entryways poke through the greenage.
Ivy, particularly English ivy (the species most often seen growing in our area), is a member of the aralia family and is native to Europe and western Asia. It can be a beautiful addition to any landscape and can provide excellent ornamentation to trees, fences and garden walls. Its lush aesthetic appeal can't be denied.
However, when left unchecked, it becomes an invader that can grow out of control almost virulently, can be extremely difficult to remove and can damage those same trees, buildings and fences on which it earlier looked so good.
In some cases, ivy can cause permanent displacement of native plant populations. As an aggressive invader, it can escape landscapes to overrun forest ecosystems. The Oregon Dept. of Agriculture has even gone so far as to ban the transport, sale or propagation of English ivy in Oregon, labeling it as an invasive, noxious weed that out-competes native plants.
When a tree fully or partially engulfed with ivy shows signs of distress, it is tempting to assume that the ivy is "strangling" the tree. While this may be a little simplistic, the ivy does often out-compete the tree for nutrients and resources, leading to the tree's death.
Ivy can harm otherwise healthy trees. Since ivy's leaf cover is so thorough, a complete covering of ivy can prohibit sunlight from reaching the tree, especially when the vine grows large enough to cover branches and the tree's own leaves. English ivy loves full sunlight and tends to keep growing up the tree in search of light. As the ivy climbs, it often begins to kill the leaves that it covers, resulting in the tree's death from the ground up.