Invasive Weed of the Month: English Ivy
By Cathy McQueeney
English ivy (Hedera helix) may conjure up images of cozy, country cottages, but don’t be deceived. This invasive weed can destroy buildings, poison pets and topple trees.
Ivy grows quickly, requires little maintenance and provides a “no-mow” evergreen ground cover. These characteristics have made it a popular ornamental plant. Unfortunately, these are the same things that have led to it being designated as a Class B noxious weed in Oregon. This means that it is a regulated weed of economic importance which is regionally abundant. It also means that the propagation, transport and sale of this plant are prohibited by law.
Ivy is native to Europe and Asia, extending down into Northern Africa. It was introduced to the United States in the 1700s as an ornamental plant. Like many landscaping plants, however, it quickly naturalized and spread aggressively into our residential and natural areas. Ivy is abundant in Clackamas County. You’ve probably seen it carpeting the ground in a natural area, or possibly covering a wall. Maybe you’ve seen it climbing high up in a tree.
How Do I Know if it’s English Ivy?
There are actually three, similar-looking, ivy (Hedera) species in Oregon that are referred to collectively as “English” ivy. These include English ivy (Hedera helix), Atlantic ivy (H. hibernica), and Persian ivy (H. colchica). Distinguishing between the ivies can be difficult and often requires a microscope to tell them apart. Ivy identification is a hotly debated topic among the District WeedWise staff! A good rule for landowners is, “If it’s ivy, it’s a problem to be managed.”
English and Atlantic ivy are also known as “Baltic,” “Irish,” “European” and “common” ivy. Both of these types of ivy are listed as noxious weeds here in Oregon.
How Can I Identify Ivy?
Ivy is an evergreen, perennial climbing vine. Vines can grow up to 100 feet long and older stems can grow up to one foot in diameter. It is a hardy plant, with specimens living for up to 400 years. Roots form along the stem, allowing it to attach to either the ground or vertical surfaces. A hardy opportunist, ivy can continue to grow through the winter months when other plants are dormant.
Ivy has both a juvenile and mature stage. To reach maturity, the juvenile plant must grow vertically on something like a tree, fence, wall, building or even a small hill. Flowers and berries will only appear on mature ivy. The flowers are small, greenish-white and grow in umbrella-shaped clusters and berries are purplish-black. Many birds, especially starlings and robins, will eat them and disperse the seeds widely from the parent plants.
Juvenile ivy leaves alternate on the stem and are leathery, with 3-5 lobes. Mature leaves tend to be un-lobed and diamond-shaped. So many cultivated varieties of ivy exist, however, that leaves are an unreliable feature for identification.
Why Should I Care About English Ivy?
Ivy grows in thick mats, blocking sunlight and crowding out other plants, including native plants, in our natural areas. The loss of native plants decreases the availability of food and cover for our native wildlife. It also inhibits the ability for new trees, shrubs and ground cover plants from getting established. This creates what some call an “ivy desert.”
Climbing ivy can be very damaging to trees and forests. Ivy vines can trap moisture against the trunk of a tree, inviting rot and pests. Left to grow, the ivy can spread into the tree canopy. Trees can topple from the additional weight, especially in high wind storms and when the ground is wet or saturated. Trees are not the only casualties of ivy. Ivy can damage buildings, fences and other structures when invading roots widen existing cracks, allowing moisture to penetrate.
Additionally, these invasive plants contain chemicals which can cause severe dermatitis in sensitive humans. There have also been reports of poisoning in cattle, dogs, and sheep when they have consumed English ivy leaves.
Finally, ivy can be a concern with our increasing incidence of wildfires. Oils found in the thick skin of holly leaves produce a flammable vapor when heated, which causes them to ignite easily. Unfortunately, this means that holly can be a dangerous ladder fuel both in our natural areas and urban neighborhoods.
How Can I Control Ivy?
Pull ivy from the ground and off trees when still young and pliable. Older, thicker stems require cutting tools. Be sure to wear gloves and long sleeves. Ivy can be a skin irritant (although not in the same way as the infamous poison ivy or poison oak). Remove all runners from the ground because remaining root sections can sprout and grow.
At the minimum, remove ivy from trees both to prevent the trees from falling, and to prevent the ivy from maturing and producing seed. Be sure to clear the ivy around the tree base as it will quickly grow right back up the trunk.
Ivy can decompose on site, as long as roots are placed in such a way to prevent them from touching the soil and growing. Monitor sites for sprouting vines. Be aware that extensive pulling operations can disturb the soil. This can provide a place for other plants to move in, both native and invasive. Be sure to follow up and pull new growth as necessary.
For more information on ivy control, check out the Weedwise Program Best Management Practices for English Ivy. Questions about English ivy or its control? Contact the Clackamas Soil and Water Conservation District at 503-210-6000.