English ivy suffers a most profound duality. While at once refusing to grow where we want it to, escapees can naturalize to engulf whole landscapes. This is just one aspect of an insidious spreader that has wrecked havoc unparalleled in the annals of horticulture.
Though it is commonly known as English ivy, Hedera helix is actually native to Europe, western Asia and northern Africa. It is an evergreen that takes on various forms and behaviors depending on conditions. On flat land it becomes a groundcover, rooting as it travels to produce dense stands of foliage. This rooting also makes it a first class erosion control plant creating seas of deep green leaves.
What makes English ivy so dicey, though, is the fact that it climbs aggressively. This quality led to its long time use of cloaking ugly fences and walls with greenery. Tendrils grow semiwoody and lined with dense modified roots that cling to any surface they contact. The roots exude a kind of natural plant glue to help them stick tenaciously. This substance can invade deep into porous materials such as mortar.
Once attached the runners grow ever larger in diameter. Very old specimens produce main branches up to one foot in diameter.
Problems with this plant manifest in a variety of ways. The clinging roots become so anchored in brick or mortar than when removed they take a good deal of the masonry with them. This can be devastating to older structures when the plants are stripped off for restoration, painting or repair. Residual bases of the roots can remain attached , leaving an unattractive pattern wherever they grew. When ivy adheres to wood structures the results can be even more destructive. The runners can invade gaps between siding boards or stretch into rafters and under roofing materials. As these eighth inch tendrils grow woody and expand in diameter, they can literally break the structure apart. When ivy climbs into shade trees there can be devastating results.
In gardens or landscapes poorly cared for, ivy grows rampant. It will root its way up a mature tree seeking light, wrapping its tendrils around the entire trunk. As it spreads out onto lateral branches, the tree leaves become overwhelmed. They eventually die out for lack of sun. Inch by inch ivy denies the tree’s ability to carry on photosynthesis. When enough of the foliage is compromised, the tree can no longer support itself and dies. The weight of a severe ivy infestation can make a dead or dying tree so top heavy it becomes a severe weather hazard. Finally there is the environmental damage to consider. Because all English ivy is imported from the Old World, those plants that have naturalized are dangerous exotics. It will cloak a forest floor shading out grasses and wildflowers that support wildlife. Because ivy rarely flowers it offers now direct food value. Invasiveness has proven most significant along both coasts and selected states in between where the climate and conditions are ideal. Ivy is a significant threat to botanical diversity.
Everyone who gardens must be aware of how aggressive this plant can be. Fortunately the smaller dwarf cultivars are far less of a problem and better suited to gardens. Their overall size does not support such rampant growth. Variegated dwarf forms are not only more attractive, this unusual coloration it seems to slow them down a bit.
For gardeners and homeowners who know few plants, ivy is always among the most easily identified and thus frequently sold. However, consider the risks of an established plant to your house, trees and wildlands before you buy. If you live in happy ivy country and are adjacent to unmanaged open space, there’s a good chance it will escape. If you aren’t ready to fight its natural tendency to grow rampant with regular pruning, think again. Then ask yourself if there might be a better choice for a labor friendly, eco-sensitive vine for home, fence or wall.
For information on controlling ivy infestations, click here for the No Ivy League’s helpful web site http://www.noivyleague.com/