Alien Invaders

Invasive Barberry takes over the forest floor in A Garden For All by Kathy Diemer

Invasive Barberry takes over the forest floor (photo by: Kathy Diemer)

I was horseback riding through the woods of Litchfield County with my sister the other day, and noticed masses of invasive plants and shrubs all along the trail.  I expressed concern about these unwanted residents of our landscape, and my sister looked at me and said “You should write a blog about these plants.  People need to know what to look for and what they can do.”  So, here I am trying to figure out where to start when there are over 100 plants, shrubs and trees considered invasive in Connecticut alone!  Instead of trying to tackle the whole list,  I am touching on a few that have been particularly problematic in my yard, and sharing how I am dealing with them.  I have provided a link at the end of the post where you can research invasives specific to your state, and learn what you can do to prevent and eradicate them.  Remember, we can make a difference!

Close up of Barberry branch in A Garden for All by Kathy Diemer

Close up of Barberry branch (photo by: Kathy Diemer)

Common & Japanese Barberry- Berberis vulgaris, or common barberry, is native to continental Europe and was introduced in the United States during the 17th century for producing jam from its fruits and to create thorn hedges. It quickly naturalized over large areas of the northeast and is now found sporadically across the landscape from North Carolina to Tennessee and north into Canada, where it is found with a scattered distribution in southern Ontario, Quebec and Nova Scotia. The Japanese barberry, Berberis thunbergii, was introduced in 1875 as an alternative to the common barberry, but it turned out to be an extremely problematic invasive as well; presently found in 31 states, with 17 (including Connecticut) where it is considered invasive. The fruit of Berberis vulgaris and thunbergii are dispersed by birds and small mammals.  And speaking of critters, barberry is a shrub that has been found quite inviting to ticks, especially those carrying Lyme disease, because of its tendency to form dense thickets where a variety of critters live or pass through. I dig this scourge up and put it in a trash bag (do not compost), but larger ones can be killed with repeated cutting to the ground and chemical application to the cut area (weed torches have also been considered successful).

Close-up of Garlic Mustard ready to flower in A Garden For All by Kathy Diemer

Close-up of Garlic Mustard ready to flower (photo by: Kathy Diemer)

Garlic MustardAlliaria petiolata is a non-native species originating from Europe and parts of Asia. The earliest records show it being grown on Long Island, N.Y. in 1868, where it was believed to be used for medicinal purposes and food. It has since spread throughout the eastern United States and Canada as far west as Washington, Utah, and British Columbia, causing great concern for the forests across North America.  Garlic mustard is a biennial herb that spreads by seed. Although edible for people, it is not eaten by local wildlife or insects, which makes it virtually impossible to control once it has reached a site.  It can cross-pollinate or self-pollinate, has a high seed production rate, it out competes native vegetation and it can quickly establish in a relatively stable forest understory (growing in dense shade or sunny sites). A square meter of garlic mustard can produce more than 62,000 seeds, quickly drowning out local flora and challenging the structure of plant communities on the forest floor. Garlic mustard is also allelopathic, producing chemicals that inhibit the growth of other plants and mychorrizal fungi needed for healthy tree growth and tree seedling survival.

Garlic Mustard's long tap root in A Garden For All by Kathy Diemer

Garlic Mustard’s long tap root (photo by: Kathy Diemer)

I have been fighting this plant for ten years, with some success.  I recommend pulling it in early spring before it forms flowers (it’s easy to recognize-it is the first plant to come up) making every effort to get the long tap root.  If you have too large of an area to pull, mow to the ground repeatedly to prevent it from creating seed.  I do not recommend using chemicals as garlic mustard grows in with native plants you may not want to sacrifice.

Close-up of Burning bush stem in A Garden For All by Kathy Diemer

Close-up of Burning bush stem (photo by: Kathy Diemer)

Burning BushEuonymus alatus, also known as winged euonymus, originated in Northeastern Asia, Japan and Central China, and was introduced to the U.S. around 1860 as an ornamental plant for use in landscaping. Despite its highly invasive nature, it remains very popular and is widely sold for its hardiness, winged stems and intense red foliage in the fall. Found in commercial and industrial sites, as well as park and residential landscapes, burning bush is a very real threat to a variety of habitats including forests, coastal scrublands and prairies.  Burning bush produces hundreds of berries which are eaten by birds or dropped to the ground under the shrub.  Once seedlings take hold, they quickly reproduce and form dense thickets, displacing many native woody and herbaceous plant species. My neighbor has one burning bush on their lawn, and directly across the street there are dozens upon dozens of illegitimate shrubs well over five feet tall clogging up the native understory.  While seedlings can be pulled by hand, mature shrubs must be dug up or cut to the ground; control re-sprouts by cutting again or brushing with systemic herbicides.

Close-up of Multiflora rose in A Garden For All by Kathy Diemer

Close-up of Multiflora rose (photo by: Kathy Diemer)

Multiflora roseRosa multiflora was originally introduced to the East Coast from Japan in 1886 as rootstock for cultivated roses. In the 1930’s the U.S. Soil Conservation Service advocated use of multiflora rose in soil erosion control, and experimental plantings were conducted in Missouri and Illinois as recently as the late 1960s.  It was planted in the Midwest for living fences and soil conservation, but also provided excellent escape cover and a source of winter food for wildlife. The species soon spread and became a serious invader of agricultural lands, pastures, open woodland and forest edges from the Midwest to the East Coast. It is a thorny, bushy bulldozer of a shrub that can form impenetrable thickets, easily smothering out other vegetation.

Forest edge overrun with Multiflora rose in A Garden For All by Kathy Diemer

Forest edge overrun with Multiflora rose (photo by: Kathy Diemer)

To keep this nasty rose under control in my horse pastures, we mow monthly throughout the growing season (one plant left untended will grow several feet tall and wide in one season).  We had to have a tractor come in to tear out some of the massive established stands, while smaller groupings have been maintained through repetitive cutting.

Trees strangled by Oriental bittersweet vine in A Garden For All by Kathy Diemer

Trees strangled by Oriental bittersweet vine (photo by: Kathy Diemer)

Oriental Bittersweet vineCelastrus orbiculatus is a woody vine native to China, Korea, and Japan that was introduced to North America in the mid 1860’s as an ornamental, quickly spreading throughout the temperate eastern US. Not to be confused with the native American bittersweet, Celastrus scandens has orange capsules around red fruits, while Oriental bittersweet has yellow capsules around red fruits. American bittersweet flowers and fruits are only found at the terminal ends of stems, while Oriental bittersweet flowers and fruits are found all along the stem at leaf axils.  Oriental bittersweet reproduces by seed and rhizome; and our birds consume the bright red fruit and disperse the seed at an alarming rate.  Once a vine becomes established it is capable of growing over 60 feet tall, all the while wrapping itself around the trunks of native trees and squeezing the life out of them like a boa constrictor.  The best way to control bittersweet vine is to carefully pull up the entire root system of young vines, and to cut established vines and brush with herbicide if necessary.

For more info on invasive species in your state, and what you can do to stop them visit:


  1. Judith Flaxman says:

    Perhaps another reason for the rapid proliferation of these invasives is the fact that the deer won’t touch them. They’ve eaten everything else.

    • You’re right, Judith! Our native fauna usually doesn’t like the non-natives, which only helps them to flourish. Pair that with the fast rate most of them tend to spread and I see trouble for our forests if we can’t take control of the situation. Thanks for writing!

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