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Green is usually good, but not always

January 21, 2011|Celeste Maiorana
  • English ivy, Hedera helix L, as seen here on sycamore trees along the towpath in C&O Canal National Historical Park, is considered invasive, or harmful to native ecosystems.
By Celeste Maiorana

Winter is a good time to look at, evaluate and make a plan of action concerning your trees and shrubs and woodlands. It is also a good time to notice what is evergreen and what is not. While you might think that all that's green and growing is good, it is not always true.

As you drive and walk around your neighborhood and the countryside, please take time to notice an evergreen vine that can be seen growing thickly, sometimes overwhelmingly, up trees. This is likely to be English ivy, and once you start noticing it, you might be surprised about how commonly it can be seen growing up trees in yards and along woodland edges.

Ivy is often planted as a hardy ground cover in shady areas where it is difficult to grow grass or sun-loving perennials. Once established, it needs little care.  

In your yard and on the ground, ivy is not usually a problem. Unfortunately, it is not easily contained and will grow vigorously along the ground until it finds something to climb. Once up in the air, it will flower profusely and dangle abundant fruits for birds to eat and sow seeds far and wide. Ivy can also be spread from pieces of cut vines that can root and grow if dropped in moist soils, and it can also survive and grow away from insufficiently managed compost piles.   

Not native to the United States, ivy is considered invasive, or harmful to native ecosystems in Maryland and 17 other states and Washington, D.C. It infests woodlands, forest edges, fields, hedgerows, coastal areas, salt marsh edges and other areas where some soil moisture is present. And even though it has been banned in some states, in many others, it continues to be marketed as an attractive, low maintenance, evergreen alternative to lawns.

Ivy impacts all levels of our forest ecosystems. As it climbs in search of increased light, it engulfs and kills branches by blocking light from reaching the host tree's leaves. Branch dieback proceeds from the lower to upper branches, often leaving the tree with just a small green "broccoli head." The host tree eventually succumbs entirely from this insidious and steady weakening.

In addition, the added weight of the vines makes infested trees much more susceptible to blow-over during high rain and wind events and heavy snowfalls. Trees heavily draped with ivy can be hazardous if near roads, walkways, homes and other peopled areas. On the ground, English ivy forms dense and extensive monocultures that exclude native plants. Once established in a forest, it can, in time, create an ivy desert.

Ivy is just one of many commonly sold plants, which invade and damage natural ecosystems. There are always native and non-native, non-invasive alternatives to invasive species. If you have ivy in your yard, think about replacing it. Or try to keep it contained and on the ground.

If you are reluctant to cut ivy off your trees because you think that the dead ivy vines will be unsightly until they finally fall from the tree, keep this in mind: All those who love trees and forests will thank you from the bottom of their hearts each and every time they walk or drive by and see those dead ivy vines clinging to your liberated tree.  



Celeste Maiorana is a member of the Washington County Forest Conservancy District Board, which promotes forest conservation in Washington County. For more information and useful links on this and other topics, please visit the Board's website at www.wcfb.sailorsite.net.

Reference: English Ivy Fact Sheet, http://www.nps.gov/plants/alien/fact/hehe1.htm, authored by Jil M. Swearingen, National Park Service, Washington, DC & Sandra Diedrich

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