English ivy is not itself parasitic to trees, but it competes for light and nutrients with its host tree and adds considerable weight, increasing the chance of trees or large branches breaking off and falling during stormy weather.
English ivy is one of many non-native species introduced in the United States for its decorative appeal. Like many innocently imported species, English ivy can be invasive, damaging trees and structures with extended growth. It is best used in a controlled environment or completely removed.
English ivy (Hedera helix) is a member of the Arilia, or ginseng, family. A native plant in Europe, western Asia and northern Africa, it was first introduced into the United States during the Colonial era. This evergreen leafy vine enjoys shade in woodlands and forests and can be found along coastal regions and marshes as well. Leaves are lobed with three or five points and usually variegated in color with shades of green and white. It can survive in a wide range of climates and soils and is comfortable in U.S. Department of Agriculture plant hardiness zones 5 to 11.
English ivy climbs up trees and walls by attaching with suction-cup-like roots called "hold fasts," sometimes spelled "holdfasts." These little attachments are so strong that they often need to be removed from walls with sandblasting. As it grows, the vine becomes thick, sometimes reaching the width of an arm. Ivy reaches full maturity only when it climbs and grows flowers and seed balls at the top portions.
Although the ivy itself does not kill a tree, the resulting actions after the ivy has started growing can. By creating competition for nutrients, water and sunlight, ivy makes a tree weaker and more prone to disease and branch dieback. English ivy also contributes to added moisture around the bark, attracting bugs and accelerating rot. It grows from the ground up, so branch dieback is usually evident at the bottom of the tree first. This leaves the tree looking like a stalk of broccoli with a head at the top of the tree. The imbalance in branches, along with the added weight of the ivy at the top of the tree, makes a tree more prone to falling during drastic weather patterns.
If you wish to keep ivy for its decorative appearance, keep it from climbing. Allowing it to climb allows it to reach maturity, so keeping it on the ground will essentially neuter the plant. Once a tree has been infiltrated, the best remediation is to kill the ivy without removing it. Clip it at the bottom around the circumference of the trunk and pull the roots out of the ground in a circle 2 feet around the tree. Leave the ivy intact on the tree, since removing it can cause the hold fasts to pull off pieces of bark, further weakening the tree. The ivy will wilt and die and in time the tree trunk will grow around the old vines.