Mulberry weed is the bane of my existence. What begins as a tiny green floret soon grows into a two to three-foot-tall hairy monster. Also known as hairy crabweed, this plant begins prolifically releasing its tiny seeds in all directions when it is less than six inches high. Its ability to seemingly disguise itself among look-alike plants, like lemon balm, makes its march across my garden that much more insidious.
Deb Weissler
Mulberry Weed
According to the Lewis Ginter Botanical Garden in Richmond, mulberry weed is now one of its “dirty dozen” that has crept into their planting beds. It has stayed under the radar in many states including Virginia, but California, Alabama and Georgia include this plant on their invasive species lists or laws.
Invasive plants are everywhere, traveling by sea, air, and even on the soles of our shoes to get here. Some have been introduced by well-meaning horticulturists and conservation groups. As international trade has exploded, so has the number of invasive species, both flora and fauna. Some have been here for over a century and are just making themselves known.
Most introduced species cause few problems. Tens of thousands of plant varieties have been introduced to North America since the beginning of colonization. Likewise, native plants have been collected and sent oversees with equal success. Of these introductions, many have successfully naturalized. Three percent of Virginia’s flora has been assessed as invasive, defined as a nonnative species capable of overtaking natural communities and creating habitat destruction.
Invasive plants proliferate and aggressively replace native plants, reduce wildlife habitat and alter natural communities. These plants typically exhibit rapid growth, prolific seed production and dispersal, rampant spread, the ability to outcompete native species, and are costly to remove or control. Some have altered entire rangelands, clogged waterways, overcome power lines and displaced crops. It has been described as a slow motion explosion, which left unchecked can alter a landscape forever.
Each state has a different list of invasive plants. The Virginia Department of Conservation and Recreation’s Division of Natural Heritage currently identifies 90 invasive plant species that threaten or potentially threaten our natural areas, parks and other protected lands. Some were never intended for our gardens but have moved in and thrived. A few may surprise you.
Deb Weissler
Japanese Stilt Grass
JAPANESE STILTGRASS
Japanese stiltgrass threatens native plants and natural habitats in much of the eastern United States. Native to parts of Asia, this plant was first documented in Tennessee in 1919 and was accidentally introduced here through its use as packing material.
Stiltgrass thrives in moderate to dense shade that has been subject to disturbance: flooding, mowing, tilling, and high foot traffic. It is commonly found along roadways, ditches, floodplains, moist woodlands, and power line corridors. Stiltgrass forms dense groves of upright grasses that resembles miniature bamboo. It is an annual grass that germinates in the spring, grows to heights of two to three feet and dies back in late fall. In late summer the plants generate flower spikes from which dry fruits are produced.
Small patches are easy to pull, but each plant can produce thousands of seeds and before long a forest of them can overtake your land. Once in the soil, seeds can remain viable for up to three years. The seeds are small and easily stick to clothing, shoes and animal fur, which aid its spread.
BAMBOO
A drive along the Yorktown battlefields reveals a large stance of impenetrable bamboo that neither Washington nor Cornwallis had to battle through. Bamboo can grow inches in a single day. The National Park Service has attempted removal of the aggressive golden bamboo that nearly surrounds the historic Shiloh Church cemetery adjacent to the property. In some places the 40 to 60 foot stalks create an impenetrable forest deprived of sunlight.
Well-meaning garden centers and online merchants continue to sell several varieties of bamboo as ornamentals without disclosing its invasive nature. Uninformed gardeners fail to plant them in deep, underground plastic barriers to restrict its growth. If left unchecked, bamboo is known for running wild. It is spread by rhizomes that can spread underground for yards, burrowing under foundations, driveways and into your neighbors’ yards. Weed-suppressant ground covers will not stop it. Some states bar its sale. In Virginia, the 2017 General Assembly passed a bill that ordered local authorities to adopt ordinances requiring proper upkeep and prohibited its spread beyond a landowner’s property.
BURNING BUSH
Burning bush is famous for its almost neon-red fall color. While this quality has made the shrub an ornamental staple in many landscapes it has also become all too invasive in the woodlands of the eastern US, where it is recognized as an invasive species in 21 states. Burning bush is native to China and was brought here around 1860 as an ornamental shrub. The plants produce a prolific number of berries, and the seeds, dispersed mainly by birds, germinate easily in both sun and shade. It can also spread by root suckering. One plant can generate hundreds of others. Beneath a mature tree, hundreds of seedlings can be found.
Its sale has been banned in several Mid-Atlantic states. In Virginia, they can still be found in local garden centers, but retail stores that offer them for sale are required to display a sign warning of its invasive nature.
Despite its biblical connotation, it is a devil to eradicate. Young plants can be easily pulled by hand, and seeds should be disposed of in a way that will prevent them from escaping into the wild. Larger specimens should be dug up and disposed of, and no part of this plant should be composted.
WISTERIA
Few plants are as beautiful or fragrant as wisteria, or as invasive. Chinese Wisteria was first imported into this country in 1816, followed in 1830 by Japanese Wisteria. Because the vines grow fast, create dense shade, are extremely fragrant and attract pollinators, wisteria is a favorite plant for porches, trellises, and gazebos.
This vine grows rapidly, reaching up to 70 feet with 15 inch trunks. Because of this rapid growth and dense shade, native canopy trees, under-story trees, and shrubs are smothered or killed beneath its heavy weight. This is especially true in warm southern states, where native ecosystems are being wiped out in the path of this aggressive and fast-spreading plant. In spring, a drive through the countryside reveals entire tree groves festooned with flowering purple vines.
It is not only the vine that threatens to escape, but the brown button-like seeds found inside the wisteria’s seed pods. Wisteria pods show up a few weeks after the vine finishes blooming. As the pods dry, the seeds burst out like popcorn, landing yards away from the parent plant. Wisteria is poisonous so children and pets should not eat any part of this infamous plant.
TREE OF HEAVEN
There is nothing divine about this devilish tree. This rapidly growing deciduous tree, native to China, has become a widespread invasive species across North America. It was brought here in the late 1770s as a horticultural specimen and shade tree. Its ease of adaptation and absence of insect or disease problems made it popular in urban landscaping. These same traits have led it to spread aggressively, crowding out native plants wherever it establishes itself.
This tree produces an abundance of seeds, crowds out native species with its dense thickets and secretes a chemical into the soil that is toxic to surrounding plants. Its aggressive root system can damage pavement, sewers and building foundations.
It has also helped advance the spread of the spotted lantern fly, an invasive insect also originally from China. These insects seek out the tree of heaven as a place to lay their eggs. The spotted lantern fly, currently spreading across Pennsylvania and the Mid-Atlantic, feeds on and damages many species of native and fruit-bearing trees.
CHINESE PRIVET
Though several southern states, including Virginia, have this plant on their invasive species list, Chinese privet remains a commonly sold and planted ornamental shrub. Privet grows particularly well in riparian forests, and its pollen is known to cause asthma and eczema in allergy sufferers. With few competitors, it is an ideal invasive plant. All nine species of privet currently in the Southeast are considered invasive.
It reproduces sexually through production and dispersal of seeds, and asexually via root suckers. It thrives in sun and shade, exploiting any open niche within our floodplain ecosystem, choking out native plants. Its presence in an area has resulted in the decline of butterflies, moths and bees.
Kudzu
KUDZU
This Asian vine needs no introduction. Known as “the vine that ate the South” is alive and well in Virginia. First introduced during the Philadelphia Centennial Exposition in 1876, it was touted as a great ornamental plant for its sweet-smelling blooms and sturdy vines. Today, no one remembers the blooms, but the choking carpet of vine is unforgettable!
From the 1930s through the 1950s, the Soil Conservation Service promoted it as a great tool for soil erosion control, and kudzu was planted in abundance throughout the South. Now this creeping, climbing, smothering perennial terrorizes farmers, gardeners and foresters all over the southeastern United States and into the Midwest, Northeast, and even Oregon.
There are many other unsavory plants too numerous to mention, including Autumn Olive, Multiflora Rose, Oriental Bittersweet, Japanese Honeysuckle, Crimson Barberry, Mexican Primrose; the list seems endless. Landowners and gardeners must be good land stewards. Become informed before planting and take action when mistakes are made or invasive species arrive. Take advantage of online resources such as www.dof.virginia.gov or your local Virginia Cooperative Extension. Fight back against invasion!