Invasive Species Identification & Management
In this region of the world, there are 125 non-native plants considered to be a threat to habitats and natural resources. That is a lot of plants that are extremely capable of multiplying rapidly, crowding out native species and leading to systemic ecosystem harm. It is already illegal to buy these plants from nurseries (like us!), but chances are, some of these species are already where you live. This article will describe some of the most common and destructive invasives as well as how to identify and remove them. It is important that when removing invasives, native species be planted in their space. Otherwise a new invasive will simply colonize the open soil.
This first invasive species has spread around the globe causing habitat destruction through its aggressive roots which rapidly reach new areas and can even disrupt home’s foundations. I’m referring to Japanese Knotweed (Fallopia japonica), a member of the buckwheat family that was introduced to the area in the late 1800s. While it was once sold at nurseries, by the 1930s it was listed as invasive and in many places illegal to sell. By that time though, populations had been established and Knotweed is now a common sight as you drive down the road.
Japanese Knotweed has bamboo-like stalks that turn from green to brown in the fall. The stalks are easy to spot in the winter after the leaves drop. Its leaves are vibrant green and heart shaped. It can grow to be 15 feet tall and form dense thickets. Since it spreads through its rhizomes, any disturbance to the soil where it lies can easily cause it to invade new areas. In the late summer, small winged seeds form which can be spread by the wind.
Once a stand of knotweed is established, it is extremely difficult to remove it. Prevention is key with knotweed, so if you know there is some nearby, ensure that any new areas of disturbed soil are quickly planted with fast colonizing native species such as dogwood or alder. If you are trying to remove established knotweed, start by hand pulling young shoots in the early spring. Be aware that new shoots will likely grow again, so you must be vigilant and repeat this often. The stalks are edible and taste sweet like rhubarb/ They are best when pickled or sauteed.
For larger populations, cutting down all stalks in the area and laying ½” hardware cloth has been shown to constrict new growth and limit nutrient availability to the underground rhizomes. Be aware that removing a stand of knotweed without aggressive chemicals will be a long journey. It will require continuous cutting of stalks and monitoring for spread sometimes over the course of multiple years. The edible shoots make this effort more rewarding and the opportunity to clear an invasive and grow helpful native species should never be passed up.
The next invasive species also originates from Japan and was similarly brought to the region as a nursery crop. Japanese Barberry (Berberis thunbergii) is a perennial deciduous shrub easily identifiable in winter by its numerous thorns and bright yellow wood when the stems are snapped. During the growing season it has simple small leaves which turn red in the fall to match the small red berries it grows in late summer. It can reach 6 feet tall though it is usually half that.
This plant rapidly grows in open dry areas but will also thrive in shaded damp areas. Birds enjoy the fruits and thereby spread this plant to new areas. Studies have also shown that tick populations thrive underneath Barberry’s dense leaves. Removing these plants may be one of the most effective tick control methods.
To manage Japanese Barberry, carefully pull up small plants in the Spring when the ground is wet. For larger plants, you may attempt to dig up the entire root system. When the plant is too big to fully dig up, repeatedly cutting the shoots may be the best bet to ultimately kill the plant.
Asiatic Bittersweet (Celastrus orbiculatus) is another invasive that is now extremely common throughout the state. Growing as a vine, it climbs native trees, smothering them and eventually killing them with its weight. Look for it along roadsides as a tangled mass of vertical vines in the winter and climbing leaves in the summer.
Its leaves are somewhat round with a tapered point. Small yellow flowers give way to vibrant clusters of red orange seeds in the fall that last through winter. Birds and small mammals love these seeds and spread this plant rapidly.
Like Japanese Barberry, Asiatic Bittersweet has the potential to increase tick populations and can snuff out the natural succession of plants leading to a less diverse forest community.
To control this plant, pull out the roots of small individuals when the soil is wet. For larger vines, cut the plant both on the ground and pull or cut the aerial vines. Only pull the vine if it falls down easily. Pulling on a stuck vine may damage a tree more than simply leaving the cut vine to die. Like other robust species, new shoots will sprout from cut roots, so repeated cutting is necessary. Expect to cut shoots multiple times a growing season and for at least three years. There’s a reason these plants have taken over so much area.
The next common invasive that we find at our nursery is the Multiflora Rose (Rosa multiflora). Yes it is a true rose and does produce pretty flowers, however this plant spreads rapidly and has some of the most painful thorns we know of.
Nasty thorns on a multiflora rose stalk.
In the winter the plant is identifiable by its arching green and purple canes with long recurved thorns. In the summer, look for pale white to pink flowers clustered at the tips of branches. In the fall these flowers turn to small red rose hips, or berries. These berries are edible and loved by wildlife. Of all the plants mentioned, this is the one that we let lie the most. If you don’t want this rose to take over, repeated cutting of its canes is the best method.
The last species that we are at odds with is Field Bindweed (Convolvulus arvensis). This Eurasian transplant is one of the most damaging plants out there due to its tremendous ability to climb, spread via rhizome, survive drought and produce viable seeds. Bindweed root systems have been documented growing 20 feet deep and whenever a shoot is severed, new growth will sprout. Control methods include pulling shoots on a regular basis to limit energy going to the roots, although this may seem to be a Sisyphean task. Applying landscape fabric to smother a large area is another option, however this has the drawbacks of plastic use and potentially killing native plants. We still have not found a great solution to Bindweed, so the best method is prevention. Weeding young seedlings when you buy plants and keeping an eye on any compost or mulch you buy is the best option.
Field Bindweed bringing down the otherwise upright stalks of Stinging Nettle
Each of these invasives can be the bane of a gardener and we are lucky enough to be dealing with all of them at once. No matter how tired we get from hand weeding, spreading beneficial native species is worth it. If you need help with identification or management feel free to give us a call and we can lend a hand in your garden as well.
