Many of us participate in garlic mustard pulls at Cold Spring Park and read about the Audubon survey of the invasive plants in Nahanton Park, but some of us don’t notice that we have invasive plants in our own yards. They’ve become established climbing up our trees, twining through our shrubs, and getting lost among our perennials.
Why is that a problem? First, because eventually they may displace the plants that we’ve chosen to put into our gardens, but, more importantly, because from their hiding spots in our yards, these invasive plants will produce seeds that will be eaten by birds, squirrels, chipmunks, and other animals and excreted in other areas, from which they will continue their spread. (Interestingly, ingested seeds have a higher germination rate than do seeds that just have fallen to the ground.) Thus, just because we don’t see a particular invasive plant taking over in our yards does not mean that it is not spreading. Invasions by plants like these are a leading cause of extinction and biodiversity loss.
Here are five increasingly common invasive plants that can be found in yards throughout Newton. (All of the accompanying photos were taken within a few blocks of my Newton Centre house.)
Oriental Bittersweet (Celastrus orbiculatus) is a deciduous vine that is the heartiest and perhaps most widespread of Newton’s invasive plant community: older vines can grow to be 4 inches in diameter and 60 feet tall. Oriental bittersweet can be found winding its way around trees and shrubs in yards, open spaces, and even densely shaded woods. It is spread not only by birds and mammals but also by people who are attracted to its showy deep orange fruits surrounded by the yellow-orange wings of the open pods and use the vine to make decorative fall wreaths. If left to grow, the vine can kill trees by girdling or smothering them; it kills shorter plants by covering them and preventing photosynthesis. It was introduced to the United States from China in the 1860s and first appeared in Massachusetts in 1919.
Black Swallow-wort (Cynanchum louiseae), a perennial vine with purple star-shaped flowers and thin pods, was brought to Ipswich from Europe in 1854 and was noted to have escaped into the wild from a Cambridge garden by 1867. It is extremely invasive and since has spread through New England gardens and into wild areas in the Northeast, the Midwest, and California. It can spread by winddispersed seed or underground rhizomes. In the wild, fields of established grass and goldenrod can be taken over by this invasive vine. It also has replaced milkweed populations, and initial investigations into its effect on the monarch butterfly, which requires milkweed for reproduction, indicate that the butterflies will lay eggs on the swallowwort plants, but the larvae do not survive. Because it is not a good food source for native birds, they, too, decline when black swallow-wort becomes dominant. Learn more about this plant.
Climbing Nightshade (Solanum dulcamara), a vine in the potato family, has beautiful purple flowers with yellow centers in the summer and bright red berries in the fall; it has distinctive, deeply lobed three-part leaves that are shaped somewhat like a lop-sided three-leaf clovers. Its berry is very poisonous to humans and livestock but edible for the birds that disperse its seeds; the leaves, too, are highly toxic to people. In Newton, the vines often are seen climbing over hedges. It was introduced to the United States from Europe for ornamental and medicinal uses and became widespread by the 1800s.
Multiflora Rose (Rosa multiflora) originally was brought to the United States from Japan because its hardiness made it seem ideal for erosion control and living fences. As late as 1960, state conservation departments recommended it as an ornamental planting that would provide food for wildlife and even distributed cuttings to landowners for free. Ultimately, they learned that it forms dense thickets in woods—and yards—and crowds out the less aggressive native plants. Furthermore, it is spread easily by birds (especially mockingbirds, cedar waxwings, and robins). A single plant can produce over 500,000 seeds (a million by some estimates) each year, which can remain viable for up to twenty years.
Garlic Mustard (Alliaria petiolata) was brought to the U.S. from Europe in the mid 1800s as a cooking and medicinal herb. Unfortunately, in spite of its benefits, it invades fields and woodlands displacing native plants. Garlic mustard changes soil conditions to inhibit the growth of many other plants. It’s been found in Newton’s woodlands for years but recently has found its way into our yards as well. It’s a biennial herb that remains as a low rosette for its first year and then in the second year has heartshaped leaves with toothed edges that grow from 6 to 36 inches tall. (If you’re not sure whether a plant is garlic mustard, just crush a leaf. If it has a light garlic scent, it is.) In May small white flowers appear and then are replaced by hundreds to thousands of tiny black seeds that are easily dispersed by the wind, allowing the plant to spread at an alarming rate. Early in the spring, the young plants can outcompete the less-hardy native plants, but they do not provide food for wildlife as the native plants do.
All of us will do a favor for the Newton’s environment in if we check our yards for these five invaders and remove any that we find, preferably before they have gone to seed. Do not put any seed-bearing invasive plants or their roots into compost or city yard-waste bags because that will help to disperse them even more. Finally, planting native plants in place of the removed invasive plants will help to keep them from returning.
Information about these and other common invasives such as Japanese barberry, Winged euonymus, and Creeping buttercup can be found in the Invasive Plant Atlas of New England.