Know your Invasive Plants-English Ivy
By Roger Simpson
As time goes by our understanding grows larger of what is an invasive plant. And along with this, our list of what plants are invasive grows also. This is the case with English Ivy. Until recently it was one of the most common ground covers. It was considered valuable for covering walls, rocks, or any rough surface. It was especially useful for growing under trees in the shade where grass could not be maintained. But things change, and English Ivy (hedera helix) is now considered an invasive plant. An invasive plant has the ability to thrive and spread outside its natural range. A naturally aggressive plant may be especially invasive when it is introduced to a new habitat. An invasive species that colonizes a new area may gain an ecological edge since the insects, diseases, and foraging animals that keep its growth in check in its native range are not in its new habitat.
Some invasive plants are worse than others. Many invasive plants continue to be admired by gardeners who may not be aware of their weedy nature. Others are recognized as weeds but property owners fail to do their part in preventing their spread. Some do not even become invasive until they are neglected for a long time. Invasive plants are not all equally invasive. Some only colonize small areas and do not do so aggressively. Others may spread and come to dominate large areas in just a few years. It’s a matter of ecology. In many cases, plants from other parts of the world are welcomed, manageable additions to our gardens. However, in some situations these non-native species cause serious ecological disturbances. In the worst cases, invasive plants like mile-a-minute, purple loosestrife, and kudzu ruthlessly choke out other plant life. This puts extreme pressure on native plants and animals, and threatened species may succumb to this pressure.
Ultimately, invasive plants alter habitats and reduce biodiversity. English Ivy is dangerous because it can spread very quickly through native woodlands, both by it’s creeping runners, and by seed scattered by birds that eat the berries. As it spreads, native plants are reduced until we are left with a very simplified ecosystem.
The problem with English Ivy is that it climbs with the use of aerial rootlets and will in time cover and kill trees. Hedera helix grows by spreading runners which climb over and smother anything and everything in their path including buildings, shrubs, and trees. If you’re a homeowner, you really do not want this plant climbing up your walls. The rootlets will burrow into masonry, eventually weakening them to the point of collapse. On wooden siding the dense cover retains moisture, which causes fungus and decay, while the rootlets pry apart siding and eventually rip your outer walls apart. As a ground cover, the quick growth and dense cover shade out native plants and suppress their growth. In tree canopies, the enormous weight of the Ivy will eventually topple each tree. The rootlets burrow under the bark, causing fungus and decay while creating opportunities for disease to enter. English ivy carries Bacterial Leaf Scorch (Xylella fastidiosa), a plant pathogen harmful to elms, oaks, maples, & other native trees.
There are two forms of English Ivy, immature and mature. The immature form has deeply lobed leaves. The mature form’s leaves, show here, are not lobed. The mature form with flowers and berries does not appear until the vine begins to grow vertically. The English Ivy Vine can grow very large, this one was larger around than a man’s arm. It gets bigger.
Early this spring it was if I awakened from a deep sleep and really took a look at two large maple trees growing in my yard. One in particular was covered with English Ivy. Perhaps the ivy stood out more on the tree before the trees leaves emerged in the spring. But for what ever reason, the realization came to me that if something was not done quickly, the tree could die. And this was an old large maple tree. What is the tree’s value, and how
long would be take to replace a tree its size? According to experts, the vines would have to be physically stripped from the tree. This turned out to be tougher than thought. By this time the vines at the bottom of the tree were larger than a man’s arm and very tough. It was recommended that all the vines be removed from six feet above the ground down. I started at chest height because it was easier to work. The vine was so thick that a combination of a tree saw and machete had to be used to cut through them . I found that the vines had to be cut and removed in lengths of about a foot. Longer lengths were simply too hard to remove. Because the ivy attaches itself with the aerial roots, after the lengths were cut, they had to be pried off with a small crow bar.
This was not easy work and very time consuming as there were vines all the way around the tree. I was lucky in that the tree was in the corner of my yard. Every time there was some extra time, I would go work on the tree for an hour. Even after the vines had all been cut and stripped down to the ground, it still took the vines in the trees a month or so to dry out and die. The leaves lived on the nutrients stored in the vine itself. Even today, months after, there are several very small lengths of vine still green but the great majority is brown and dried. The tree has leaved out and appears to be none the worst for wear. But the message is clear, avoidance is better than remedy. If you have English Ivy, the best bet is to never let it climb into any tree. Ivy can cover a tree or building, but it might take several years. Beside the weight of the vine, it slowly smothers the tree and promotes disease.