Jenny AngelEven if you don’t know its name, you’ve likely seen black swallow-wort around town. This twining vine with narrow, glossy leaves is as likely to lurk in shadow among the branches of a privet hedge as sprawl across a chain-link fence. When you try to pull it, white rhizomes beneath the ground hold fast and easily break off, mocking your effort. A new plant can regrow from a tiny piece of rhizome.
But this weed is worth our attempts at eradication. Introduced from the Mediterranean region to Essex County, Mass. in the mid-1800s as an ornamental, the vine is named for the dark purple— almost black—color of its tiny star-shaped flowers and the swallow-winged shape of its elongated seed pods; “wort” is the Old English word for “plant.” Like other invasive species, it arrived into a new habitat free of the ecological controls—such as leaf-eating insects—that kept it from growing out of control in its native range. It is so pervasive in New England today that a more fitting name might be “mini kudzu of the north.”
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Black swallow-wort (Vincetoxicum nigrum)—and its lighter-flowered cousin, pale swallow-wort—are members of the milkweed plant family, so-named for their white sap, which is toxic to many animals (and irritating to gardeners’ skin). Milkweed seeds develop in conspicuous long pods that split open when ripe; silky fluff attached to each seed acts like a sail, catching the wind, and dispersing the plant’s offspring near and far.
Species of milkweed native to North America, including common milkweed, butterfly weed, and swamp milkweed, are important to the life cycle of monarch butterflies. Their nectar attracts the butterflies, who in turn aid in pollinating the plants, and their unique leaf chemistry of milkweeds attracts female monarchs seeking a place to lay their eggs. Through a nifty bit of alchemy, the caterpillar hatchlings are not poisoned as they chew on the leaves. Instead, they co-opt the plant’s weapon as their own. The caterpillars store the poison in their bodies, making themselves toxic to would-be predators such as birds. Thousands of years of co-evolution of plant and animal have choreographed this intricate ballet.
Alas, monarchs will also lay their eggs on swallow-wort, especially where it has displaced native milkweeds. The European swallow-worts, which did not co-evolve with monarchs, have leaf toxins that caterpillars cannot process. Instead, the caterpillars die. By running rampant across New England, swallow-wort contributes to the dwindling numbers of monarchs.
Taking a few small steps at eradication on your own property can help. Look for the plant in late spring, and use a trowel or tool to dig out as much of the root and rhizomes as you can. Wear gloves and long sleeves, and keep children and pets away, because of the toxicity. At this time of year, late summer, if it’s too overwhelming to dig up mature plants, you can still make a dent in next year’s crop by removing the green pods. Most important: Bag all plants, roots, and pods in plastic; tie off or seal the bag; dispose in the trash. Do not put swallow-wort or other noxious weeds in yard waste or compost, as you will likely just be helping the plant spread to new places! Finally, focus on your own property and on gently educating friends and neighbors. Offer your free labor if you wish, but don’t pull from public land or a neighbor’s property without permission.
Frank Sartori of the Department of Public Works suggests that people who want to organize a “pulling party” should coordinate with the DPW and the Recreation Department before doing any work at town playgrounds and school grounds.
Angus Abercrombie of Belmont’s Conservation Commission stresses that the rules at Rock Meadow forbid damaging or removing plants, even invasives. Still, he expects there will be opportunities for people to help tackle weeds during planned efforts in the future.
Organized efforts to pull various invasives at Lone Tree Hill are scheduled from time to time; look for their postings hereand online. Another option is to join Mass Audubon Habitat’s Pulling Partners, who meet on Wednesdays after school and were featured in the Belmont Voice last week.
Jenny Angel has been gardening in Belmont since 2001 and became a member of the Belmont Garden Club in 2019. From 2010 to 2013 she was the volunteer editor for the Belmont Farmers’ Market newsletter, “Roots & Sprouts.” As a Garden Gems columnist, she is excited to delve into Belmont’s horticultural history and current greenspaces as well as share tips from local experts on diverse aspects of gardening and related pursuits.