Contact: Carole Bergmann | Carole.Bergmann@mncppc-md.org
ANNAPOLIS, MD (February 2004) – Institutions of higher learning in our country are sometimes described as “ivory towers.” For February’s Invader of the Month, the Maryland Invasive Species Council examines “ivy towers”, the columns that English ivy, Hedera helix, makes when it scales buildings or forest trees. English ivy is frequently used in home and commercial landscapes as a ground cover, primarily in shady situations. It is a vigorous grower, with few insect, disease or cultural problems, and for the first few years can be a low-maintenance plant. Easy to propagate, it is a relatively inexpensive ground cover.
The problem is that, without annual pruning, English ivy outgrows its original planting area, and climbs, attaching to trees, buildings, or anything else. Because it attaches to buildings by the use of “holdfast” roots, it can cause damage to tree bark, wood and masonry, a maintenance problem well known to property owners with ivy plantings. Even when it stays on the ground, English ivy can outgrow the bounds of the garden where it was originally planted, and grow into neighboring properties, including woodlands. This happens frequently in woodland buffer areas that adjoin residential neighborhoods, such as Rock Creek Park in Washington, DC and Maryland.
English ivy is a woody vine with dark green three- to five-lobed leaves, with heart-shaped bases and lighter colored veins. The form that we are most familiar with is sexually immature; it does not flower and seed. When allowed to climb and with sufficient light, however, it becomes sexually mature. The leaves take on a more triangular or egg-like shape, and the plants produce clusters of small greenish white flowers in the fall and then black fleshy berries with one or more hard seeds in the spring. The berries are eaten by birds, and the seed spread in bird droppings, and the plant is thus easily moved into areas where it was never intended to be planted. English ivy is also spread in improperly disposed of garden debris – it roots very easily from pruned pieces discarded at the side of the road.
Introduced into this country by colonists from Eurasia, English ivy today is widely sold as an ornamental plant. It inhabits not only gardens, but hedgerows, woodlands, coastal areas, salt marsh and field edges. It is extremely competitive, even in shady areas, although it does not do well in very wet conditions.
Once the ivy escapes gardens and grows into parklands and natural areas, it causes several types of damage.
1. It decreases biodiversity because it creates such a dense ground cover that it out-competes native woodland plants, which are often also under attack by white-tailed deer.
2. It damages trees, both through the glue-like substance that helps its holdfasts attach to bark, and through limb fall caused by the weight of the vines. Sometimes this extra weight can bring whole trees down, especially in ice storms.
Control of English Ivy not only involves removal, but also follow-up monitoring, and may require recolonization by planting native shrubs, small trees and wildflowers, especially in natural areas.
In most situations, wholesale, non-selective methods, such as spraying with an herbicide, should be avoided. Non-selective methods often result in the removal of desirable woodland species that may persist in the understory, like viburnums, blueberries or ferns. If possible, remove English ivy by hand.
The first step is to cut, near ground level, all the vines that are climbing trees. This will prevent further fruiting and seed dispersal, and will unburden the trees. It is not necessary to pull the vines from the trees, in fact, this may often do more harm than good.
The next step is to cut the ivy roots and to roll the mass of ivy vegetation as the roots are cut, much like rolling up a giant carpet. This is hard, dirty work, and it helps to have two or more people engaged in the process, but it is not as enormous a task as it may seem.
Step three of the process is to help native plants recolonize the woodland understory. This is crucial, because nature abhors a vacuum, and removal of the ivy disturbs the soil, creating an opportunity for colonization by other, aggressive, potentially more troublesome, invasive plants, such as Japanese stilt grass, Garlic mustard, Multiflora rose, or Japanese honeysuckle. The likelihood of simply swapping one invasive plant species for another means that natural area managers (including homeowners with woods on their properties) must be especially careful when attempting remediation of woodlands infested with English ivy. Often small bare root native woody plants are available for a relatively low cost per plant. Seed mixes of native woodland wildflowers are also available, and can be broadcast throughout the area where ivy has been removed.
No English ivy removal project is complete without follow-up monitoring. The final, and ongoing, step is to vigilantly scout for and remove any invasive plants (including ivy missed in the removal process) in the replanted area. As long as unmaintained English ivy is planted in gardens adjacent to natural areas, there will always be the potential for reinvasion.
Because of its potential to invade woodland environments, MISC urges homeowners and landscapers alike to consider alternatives to English ivy in most garden applications. In the average suburban landscape, there are other ground covers that may be substituted for English ivy. Some of them are:
- Liriope, or lily turf, is taller, and has spikes of small, attractive purple or white flowers. Avoid the species, Liriope spicata, which can spread by seed and runners.
- Allegheny pachysandra (Pachysandra procumbens), native to the Appalachian region, has a subtle silvery blaze over gray-green leaves. It has attractive spikes of tiny white flowers borne in early spring before new leaves appear.
- Hostas, while not evergreen, certainly are a terrific shady ground cover for gardens without deer.
- Epimedium, or Bishop’s Hat, is a shade perennial that slowly spreads and forms a dense cover. It has beautiful columbine-like flowers (yellow, pink, red, orange, lavender…) in early spring.
- Geranium macrorrhizum is evergreen, six to eight inches tall, with pink or white flowers in spring, and strongly herbal-scented foliage. It spreads by above-ground stems, and is easy to control.
- Foamflower (Tiarella species and hybrids) offers some great evergreen plants, both clumpers and spreaders, with white (or light pink) flowers in spring. Foamflowers tolerate shade, and prefer moist soil.
- Many evergreen ferns make nice ground covers, especially the Christmas fern, Polystichum acrostichoides, and the evergreen wood fern, Dryopteris marginalis.
- Japanese pachysandra (Pachysandra terminalis). Short, evergreen and tough, and costs about the same as English Ivy. However care must be taken to keep it from creeping beyond its bounds, especially in gardens bordering woodlands.
For more information on this and other invasive species in Maryland, visit the Maryland Invasive Species Council.