When English ivy grows large enough to encircle and cover an entire tree, the vines add a considerable amount of weight to the tree. Depending on the strength and integrity of the trunk, this can present a danger for the tree. The weight of the vine can further compromise the tree, especially during the winter months. English ivy is evergreen, meaning it remains on the tree in its entirety when the tree is at its most vulnerable state of hibernation. The winter months can present problems such as high winds and heavy snows, further adding to the stress on the tree and making it much more likely to break or fall.
Since the leaf cover of the English ivy is so complete, a thorough covering of this invasive vine can prevent sunlight from getting through to any plants growing beneath. This can rob a tree of sunlight, especially when the vine grows large enough to cover branches and the tree's own leaves. English ivy thrives in full sunlight, and will naturally try to reach the brightest light it can find. This is often done by circling its way up the trunks of trees until it reaches the canopy. As the ivy climbs, it often begins to kill the leaves that it covers, resulting in the tree's death from the ground up.
Vines of English ivy that have climbed their way up a tree trunk often spread out along the ground as well. The root structures that take hold in the ground above the tree roots act to draw out water and precious nutrients that would otherwise be used to sustain the tree. Vines and leaves around the base of the tree and roots shield the tree from water and keep decaying plant matter off the ground. This decaying matter is vital to returning nutrients back to the soil, and a thick covering of English ivy can drain the soil of its nutrients in this way.
English ivy can be very difficult to remove. Most instances will require multiple attempts to rid the area of the vines; using multiple methods can often help. Removing the vines from the tree itself by hand can be effective immediately, allowing sunlight to reach the tree again and restoring the quality of the soil around it. When disposing of vines, throw them in the trash rather than on a compost or leaf pile, where seeds can spread and vines can take root again. There are a variety of chemical compounds that are readily available for controlling weeds and invasive plants that can be effective in controlling new growth; selecting the right herbicide geared for weeds and vines will control English ivy without hurting the tree if applied according to directions.