Old Backyard Favorites can be Invasive in Naturalized Areas

Many of the attractive plants we’ve loved and used for decades in our yards and other settings are increasingly being recognized as invasive in naturalized settings.  In the surrounding woodlands, meadows and prairies, along roadways and in our local parks in Central Ohio, we are seeing large, dense stands of these non-native invasive plants, which can out-compete other native plants. Some of the most common in central Ohio include wintercreeper, Asian bush honeysuckle, myrtle, privet and burning bush.

Wintercreeper, or creeping euonymus, Euonymus fortunei, is an extremely aggressive evergreen perennial vine.  An article on wintercreeper was published in the FLOW Newsletter in January 2024.  Asian bush honeysuckle, perhaps the most widespread invasive shrub in central Ohio, was also reviewed in a FLOW article.

In this month’s newsletter we’ll discuss the problems with two other of these long used but invasive plants–myrtle and English Ivy – when they accidentally escape our property or are intentionally planted in woodlands or other natural settings. Any property owner whose land land is near natural areas need to be especially vigilant if they have either of these plants, which many of us still do!  Eradicating these invasives and naturalizing areas with native plants can be challenging.

Myrtle

Myrtle, (Vinca minor), also known as common or small periwinkle, is now recognized as invasive, especially in woodland areas.  Myrtle, a longtime favorite groundcover, is a member of the dogbane genus, was introduced from Europe and western Asia in the 1700s.  Because it prefers shade/part shade, and tolerates a wide variety of soil types, it spreads rapidly in forests. Growing in dense stands, it crowds out native ground plants, and even will surpress shrub and tree saplings.  Furthermore, myrtle produces a chemical that inhibits the growth of these native plants, while providing no benefits for wildlife. Fortunately, it does not climb and damage trees like wintercreeper and English Ivy, and does not spread rapidly through seed dispersion.

Myrtle is an evergreen vine that creates a groundcover, growing 3 to 6 inches tall, with dark green , glossy leaves one-half to two inches long on the opposite sides of the stem.  Flowers are purple, blue or white, blooming in March and April, and sometimes again in the fall.  Fruit is slender, cylindrical up to two inches long, splitting when dry to release three to five seeds.  However, as mentioned above, seeds are probably not a major mechanism for myrtle spreading.

Myrtle can be controlled by hand-pulling or foliar spray with glyphosate or triclopyr.  Cutting then spraying with 3% glyphosate on new growth in the spring is likely more successful to penetrate the waxy surfaces of the leaves. Hand pulling and spraying often requires follow-up spot treatment to ensure all the roots are removed or killed.  Myrtle can also be smothered with several inches of mulch kept in place for at least two years.

English Ivy

English ivy (Hedera helix) is native to Europe, western Asia and northern Africa.  It was likely brought to the US by early European settlers, and prized as a decorative evergreen groundcover and attractive climbing vine. It is also very hardy and fast-growing, tolerating a wide range of temperatures and soil types. English ivy invades woodlands and their borders with fields, hedges and, like myrtle, is often associated with old, abandoned home sites.

English Ivy has waxy, dark green leaves with lobes in juvenile plants, which gradually diminish as the plant matures.  The juvenile plants grow horizontally, and the stems can root when in contact with soil.  At this stage English ivy is a groundcover, often forming a monoculture of dense mats which, like myrtle, can smother or outcompete native plants, including shrub and tree seedlings.

After several years, as the vine matures, it often begins climbing and adhering to trees, shrubs, walls and other structures with aerial rootlets.  With sufficient light, it can produce clusters of yellow-green flowers with black-purple berries in the fall. At this stage, English ivy becomes much more detrimental. The berries are eaten by birds, providing little nutritional benefit, and becoming an important mechanism for spread. As it climbs trees seeking sunlight, often to the canopy, it shades out the tree leaves, blocking photosynthesis and can eventually kill the tree. And as the vine grows larger and heavier, it can also cause branches or entire trees to fall under its weight. This is especially problematic for trees that are diseased or stressed, and during storms when the mass of vines can act as a sail catching the wind.

Credit – Greensburgh Nature Center, Scarsdale NY

Controlling English ivy, especially when well established, can be very challenging.  Small infestations can be pulled by hand.  The more established groundcover vines can be cut at the roots and rolled up into a ball, like wintercreeper.  Foliar spray with glyphosate and triclopyr can be effective, but the effect is slow, and new leaves sprout and need to be treated. Like myrtle, it also can be smothered with several inches of mulch left in place for at least two years. These control measures will generally require followup treatment to ensure all the remaining roots are removed or the plant has been killed.

The climbing vines are a higher priority, as at this stage it spreads far more rapidly and begins damaging trees. Vines should be cut twice to remove a section, around eye level and again close to the ground, being careful not to damage the bark. It is important to cut all the vines around the tree in the section being removed. Sometimes it’s difficult to get underneath the vine to make a cut, and a small pry bar can help loosen it. The vine above the cut generally dies and trying to pull it out can further damage the tree. The freshly cut stump can be killed by treating with glyphsate or triclopyr, always following the manufacturer’s instructions.

Alternative ground covers to myrtle and English ivy include: moss phlox (Phlox sublata), green and gold (Chrysogoru virgiianum), wild pink (Silene carolinia), Allegheny pachysandra (Pachysandra procumbens), Canandian wild ginger (Asarum canadensis), white wood aster (Aster divaricatus), Virginia bluebells (Mertensia virginica).  A more in-depth listing of alternative plants for myrtle can be found at:  https://www.gardenia.net/guide/native-plant-alternatives-to-vinca-minor and for English Ivy:  https://www.gardenia.net/guide/native-plant-alternatives-to-hedera-helix.

Sources:

• USDA Forest Service & USDA National Invasive Species Information Center
• Invasive Plant Atlas of the United States
• Global Invasive Species Team, The Nature Conservancy
• Pennsylvania Department of Conservation and Natural Resources
• University of Georgia Extension Center