January Invasive Weed of the Month: Ivy

Mature ivy is cold hardy and continues to grow in winter.

Are you familiar with the invasive weed English ivy? You’ve probably seen it carpeting the ground in a natural area, or perhaps completely covering a wall, or possibly climbing high up a tree.

Like many invasive plants, ivy was introduced as an attractive ornamental plant for landscaping. However, it escaped! Now ivy has become highly invasive in forests and natural areas across western Oregon and Washington.

More than one ivy?

Did you know there are actually three similar-looking Hedera species documented in Oregon? Many people refer to all of them as English ivy, but there are three species: English ivy (Hedera helix), Atlantic ivy (H. Hibernica), and Persian ivy (H. colchica). Only the first two (H. helix and H. Hibernica) are listed as noxious weeds in Oregon. While much difficulty surrounds its identification, Atlantic ivy (H. Hibernica) is considered the most common in Oregon.

It can be difficult to tell them apart as the key distinguishing feature is microscopic hairs on the underside of juvenile leaves that can only be seen with at least 40x magnification. However, even this feature can be confusing as weather exposure can rub off these hairs.

How can I identify ivy?

English ivy berries

Ivy is an evergreen, perennial, climbing vine in the Araliaceae (ginseng) family. The vines can grow up to 100 feet long, older stems can grow to 1 foot in diameter, and it can live to be 400 years old. Wow! Roots can form along the stem that allow it to attach to either the ground or vertical surfaces.

You may see ivy in two forms, juvenile and mature. 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. Berries are purplish- black and many birds (especially starlings and robins) will eat them, though they are poisonous to mammals (including humans).

Juvenile ivy leaves alternate on the stem and are leathery, with 3 – 5 lobes. English ivy juvenile leaves are typically smaller and more deeply lobed than Atlantic ivy juvenile leaves. However, many cultivated varieties exist, making leaves an unreliable identification feature. Mature leaves for both species are unlobed and more diamond shaped.

Why should I care about invasive ivy?

English ivy in trees

One of the main impacts of ivy is that it grows in thick mats, blocking sunlight and crowding out other plants. As with other invasive weeds, the loss of native plants decreases the availability of food and cover for our wildlife. A thick carpet of ivy also inhibits the ability for new trees, shrubs, and ground-cover plants to get started, creating what some call an “ivy desert”.

When ivy climbs trees, it can be very damaging to forests. The additional weight and drag during winds can cause trees to topple, especially in high wind storms when the ground is saturated. Ivy often takes advantage in deciduous forests, where the extra winter sunlight allows it to grow while other plants are dormant.

How can I help?

Ivy can be pulled from the ground and off trees, although when the stems grow thick, cutting tools are necessary. Be sure to wear gloves and long sleeves as ivy can be a minor skin irritant (though not in the same way as the infamous “poison ivy”). When pulling ivy from the ground, all runners must be removed because remaining root sections can resprout.

Massive English ivy stem

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 base of the tree as well; ivy is determined and will quickly grow right back up the tree.

Ivy can be left on site to decompose, as long as roots are placed in such a way to prevent resprouting. Sites should be monitored for resprouting vines. Be aware that extensive pulling operations can disturb the soil, providing a place for other plants to move in, both native and invasive. Follow-up is highly encouraged! For more detailed information on control, visit our Best Management Practices on ivy.

If you have additional questions about ivy or how best to control it, please contact the WeedWise program at 503-210-6000 or [email protected].


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