Invasive Plants
Friends of Mianus River have joined forces with UCONN Master Gardener (MG) and park volunteers to address invasive plants that have overtaken the Merriebrook Lane parking areas. Thanks to donations from park lovers and a MicroGrant from the City of Stamford, we are working to return the areas to native plantings. Per the US Forest Service, “Invasive species are defined as a Non-native (or alien) to the ecosystem under consideration; and, whose introduction causes or is likely to cause economic or environmental harm or harm to human health.” Invasive plants thrive in adverse conditions, have many seeds, and crowd out native species. Ultimately, they contribute to decreased soil quality, erosion, diminished wildlife habitat, and degraded water quality.
Invasives must be eradicated before we can plant species native to the area. Given the parking area’s uneven terrain, we used a selective herbicide to destroy Mugwort, the primary invasive. For the Fishing platform, we are testing different eradication methods: spraying, smothering with wood chips, and solarization.
Smothering with Wood Chips: Place a 6-8 inch thick layer of wood over the infestation.
Solarization: Use the sun’s heat to “cook” invasives under a heavy plastic tarp.
Chemical Control: Apply a selective broadleaf herbicide to each invasive.
Invasives in the Mianus River Park:
The City of Stamford surveyed invasive plants inhabiting the City’s parks, with the following being the most prevalent at Mianus. They are listed in order of magnitude, with one having the most appearances.
Winged Euonymus/Burning Bush (Euonymus alatus): This fast-growing woody shrub, native to northeastern Asia, reaching heights of 5-15 feet, features twigs lined with thin ribs and vibrant red leaves in the fall, serving as a popular ornamental shrub for various areas; however, it's rapid spread and dense thickets pose a severe threat to local woodlands by shading out native vegetation.
Garlic Mustard (Alliaria petiolata): Garlic mustard, brought by European settlers, is a two-year herbal plant with small rosettes in the first year and 4-foot height with white flowers in the second. Emitting a garlic odor when crushed, it spreads rapidly, emitting toxins that hinder nearby plant growth, weakening the ecosystem.
Japanese Knotweed (Polygonum Cuspidatum): Japanese Knotweed is a vigorously spreading shrub with smooth, zig-zag shaped stems, broad egg-shaped leaves, and white flowers in late summer; this plant forms dense clumps, preventing the growth of other vegetation. Native to Eastern Asia, it thrives along riverbanks and roadsides, reaching heights of 3-15 feet.
Mugwort (Artemisia Vulgaris): Mugwort is a rapidly spreading herbaceous plant, two to five feet tall, native to Europe and Eastern Asia, with chrysanthemum-like leaves, varying in shape between upper and lower leaves. Commonly causing allergies, it thrives in high elevations, disturbed habitats, meadows, and roadsides, having been introduced in the 1600s for medicinal use.
Multiflora Rose (Rosa multiflora): Multiflora rose, a robust shrub with arching stems, forms dense thickets, displacing native plants. Featuring prickled branches, it blooms white flowers in May and June, followed by red hips in August. Native to Japan and Korea, it prolifically reproduces, with each plant producing up to a million seeds annually, primarily dispersed by birds.
Oriental Bittersweet (Celastrus orbiculatus): Oriental Bittersweet, a robust vine native to Korea, China, and Japan, rapidly overtakes nearby vegetation and structures. With a rapid growth rate, it can strangle shrubs and trees, reaching 20-30 feet or more with support. This invasive species outcompetes native American bittersweet and is prized for its vibrant berries in dried-flower arrangements.
Tree of Heaven (Ailanthus altissima): The tree of heaven, originating from China, is a fast-growing deciduous tree with compound leaves along reddish-brown stems. Reaching up to 80 feet, it thrives in unconventional locations like sidewalks and stone walls due to its pollution resistance and adaptability. Introduced for urban use, it outcompetes native plants, emitting a strong odor and releasing soil-toxic chemicals. Serving as a host for the invasive spotted lanternfly, it contributes to the spread of this harmful insect. Distinguished by glands at the leaflet base, it may resemble native trees like sumac or walnut.
Ground ivy (Glechoma hederacea): Ground ivy, native to Europe, is a perennial herb in the mint family that forms thick mats along the ground, with square stems and kidney-shaped, toothed leaves emitting a musky mint odor when crushed. From March to May, it has blue-violet flowers with purple spots and spreads through creeping stems in various habitats.
Black locust (Robinia pseudoacacia): The nitrogen-fixing black locust is a large deciduous tree with thorn-covered branches, reaching up to 25 m tall. Featuring compound leaves and fragrant white flowers in May-June, it reproduces vegetatively and proliferates, displacing native vegetation in disturbed areas. While native to parts of North America, it is not indigenous to New England.
Japanese Stiltgrass (Microstegium vimineum): Japanese Stiltgrass is an annual grass resembling young bamboo, reaching 1-3 ft. Its lance-shaped green leaves, sparsely hairy upper blades, and stoloniferous stems are distinctive. It reproduces by seed, with 100-1,000 seeds per plant, spreading through soil and water movement, particularly with soil disturbance.
Wineberry (Rubus phoenicolasius): Wine raspberry, a spiny shrub from eastern Asia introduced to the U.S. in 1890, invades open areas with its multi-stemmed growth. It has canes up to 9 ft, compound leaves, and produces small white flowers in spring, leading to tasty red fruit. Thriving in moist open areas, it forms dense thickets, displacing native vegetation. Reproduction occurs through seeds and root nodes.
Garden loosestrife (Lysimachia vulgaris). The garden loosestrife is a perennial flowering plant growing three to six feet tall. It has soft, hairy stems and leaves that are lance-shaped and 3-5 inches long. The leaves are usually whorled in three groups, dotted with orange or black glands. This invasive species grows in wetlands, waterways, and lakeshores, forming dense stands and outcompeting native plants.
Honeysuckle (Lonicera maackii). The honeysuckle is a flowering shrub or vine native to North America and Eurasia. It can grow 10 to 25 feet, having long, tubular flowers that may be white, yellow, orange, or pink. Invasive honeysuckles can shade out tree seedlings and outcompete native plant diversity. Honeysuckle berries have lower nutritional content than natives, causing harm to the wildlife that feed on them.
Japanese barberry (Berberis thunbergii). The Japanese barberry is a woody, spiny shrub that can grow up to 6 feet tall. It has small, oval-shaped leaves that are smooth-edged and turn red in the fall. Native to Japan and Asia, the invasive plant was introduced in the United States as an ornamental plant. The thorny shrub quickly spreads and overcrowds native plants in various ecosystems: forests, woodlands, wetlands, fields, and more.
Norway maple (Acer platanoides). The Norway maple is a large, deciduous tree native to Europe and Asia. It has lime-green flowers that bloom in April and have a sweet smell. The tree can grow approximately 40 to 60 feet and tolerate many different growing environments. The Norway maple can also spread into native woodlands and outcompete the sugar maple due to its shade tolerance and ability to survive in various living conditions.
Porcelain berry (Ampelopsis brevipedunculata). The porcelain berry is a woody, perennial vine native to northeastern Asia. It is a relative of grapes and can grow up to 20 feet tall. It resembles a wild grapevine, climbs via its tendrils, and can grow from 15 to 20 feet. The berry is an aggressive, invasive weed. It tolerates adverse conditions, often spreading to damp, shady areas like streambanks and forest edges.
Contributors:
Isabelle Kanefsky, Volunteer
Liz Gilbert, Master Gardener 2016, Advanced Master Gardener 2019
Linda Chapman, Master Gardener 2022
February 19, 2024