Top 10 Invasive Plants That Harm Our Urban Forest
Scientific Name: Privet Ligustrum sinense/lucidum/japonicum
Believe it or not, privet takes up more space in our forests than kudzu and can be just as harmful. This plant is commonly planted as a “privacy” hedge on private property. Birds then spread the berries all over the city. These shrubs are evergreen and can reach more than 30 feet tall full-grown, shading out anything trying to grow beneath them. In forests infested with mature privet, it is typical to see only older trees with no younger generations of trees growing. When these older trees fall, there will be nothing left but a privet monoculture.
Scientific Name: Wisteria sinensis/floribunda
These two invasive wisterias are commonly planted for their enchanting and fragrant flowers. This vine, which often escapes into our forests, grows aggressively. It covers the forest floor and wraps tightly around trees, starving them of nutrients needed to grow. If you cannot live without this plant in your garden, don’t fret! There is a native variety called American wisteria (Wisteria frutescens) that provides the same grape shaped beautiful flowers without the guilt.
Scientific Name: Hedera helix
English ivy is often planted as a ground cover in yards. Because it is so aggressive, it often spreads into neighboring properties and climbs trees. When growing vertically on trees or walls, it can produce berries allowing the plant to spread to other greenspaces via birds. The leaves of the vine act like a sail, catching wind on the trunk of the tree. This wind effect, combined with the weight of the vines, pulls on the tree, making them more likely to fall during a storm. When this plant spreads into our urban forests, it can pull down large trees and prevent new trees, woodland plants and wildflowers from germinating. This plant is great to keep indoors because of its effectiveness of removing pollutants from the air, improving your indoor air quality. So if you are tempted to bring some ivy into your life, plant it in a pot indoors.
Japanese Chaff Flower
Scientific Name: Achyranthes japonica
While this herbaceous perennial is fairly new to Georgia, it has been spreading like wildfire. It has “hitchhiker seeds” that stick to pant legs and loose pups in nature preserves (another reason to keep your dogs on a leash). Because of this, you will often see this plant growing along trails. This plant that breaks apart when you try to uproot it, making it very difficult to remove. It creates very dense patches up to 3 feet high, shading out any native plants below. Check yourself for seeds whenever exploring our forests! If you have a hitchhiker, be sure to dispose of it in a trash can and not on the forest floor.
Scientific Name: Lonicera japonica
Japanese honeysuckle is commonly planted. Although this plant’s flowers smell good, this vine can mean big trouble for our forests. It is the 5th most commonly observed invasive plant in the country. The vine creates a dense cover on our forest floors, covers young trees, cuts their bark and prevents them from getting the sun they need to thrive. If you are interested in planting a honeysuckle vine at your house, consider the beautiful, native Coral honeysuckle (Lonicera sempervirens) instead.
Scientific Name: Humulus japonicus
Japanese hops is a prickly vine found growing on stream banks around the city (usually with kudzu). It is fairly easy to hand pull as long as you’re wearing gloves. This vine covers streambank slopes, preventing the growth of other vegetation. Erosion along our streams results from a lack of plant diversity and deep roots that would help keep the bank in place.
Scientific Name: Fallopia japonica
Japanese Knotweed is an herbaceous plant with a hollow stem that grows up to 6 feet tall. Its dense root system and strong growth can damage concrete foundations, buildings, roads, paving, and retaining walls. It also takes over streambanks, making it difficult for water to flow down the stream efficiently. Japanese knotweed is very difficult to remove. The plant tears easily, making pulling out the roots nearly impossible. Additionally, any piece of the stem or root that rips off can travel downstream and form a new plant.
Scientific Name: Microstegium vimineum
Japanese stiltgrass is an annual grass that often covers the ground near stream corridors. Unlike most grasses, it thrives in the shade. Since it is an annual, it does not have deep roots and is easy to pull by hand. Its seeds can survive in the soil for years before they begin to grow, making this plant even harder to control. There are studies showing that this plant can release chemicals that prevent other, more beneficial plants from growing around it. So although this plant does not create as dense of a mat as our other invasive vines and grasses, it suppresses our native plants in other ways.
Scientific Name: Pueraria montana
Better known as “the plant that ate the south,” kudzu was purposefully planted all over the south in the early 20th century to reduce erosion from poor farming practices. Although kudzu is no longer planted, we are still stuck with it growing along highways, in public parks, and abandoned lots. During peak growing season, it can grow up to a foot a day! With that kind of speed, it out competes all plants in its path, including large trees by growing vertically and covering the tree canopy with its large leaves. In other countries, this plant is farmed because it has edible leaves, and the root can be used as a thickening agent for soups. Thankfully, the seeds of this plant are not much of an issue with it spreading but rather it keeps growing along the ground and developing more roots. Well-established kudzu roots can weigh up to 400 pounds! With all that energy stored, it can be a difficult plant to remove.
Mondo & Monkey Grass
Scientific Name: Ophiopogon japonicus & Liriope muscari/spicata
Monkey or Mondo grass is commonly planted in yards, right of way gardens or under trees since it grows easily in shade. It is planted for its evergreen appeal and purple flowers. Unfortunately, those flowers turn into berries that birds readily spread to our forested areas. Because this plant grows so well in the shade, it takes over the forest floor, creating thick mats (much like English ivy) suffocating our native ground layers. Native ferns are a great alternative and grow well in shade. Another good choice is Blue-eyed grass (Sisyrinchium spp.) for sunny spots!