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Cambridge declares war on invasive vine

Rebecca Ramsay observed black swallow-wort on Forest Street in Cambridge.DAVID L. RYAN/GLOBE STAFF/Globe Staff

CAMBRIDGE — It’s a problem that probably started in Cambridge a century-and-a-half ago, and now a group of Cambridge women – they call themselves the “Cambridge Pod Patrol” – are trying to do what they can to fix it.

Their target: the black swallow-wort, a type of milkweed.

Their slogan: “Spread the word, not the weed.”

Their intentions, according to experts: noble.

Their chance of winning, according to experts: none.

When they will give up, according to the Pod Patrol: never!

It all started in the mid-1800s when the black swallow-wort, a perennial, herbaceous vine native to southern Europe, was first cultivated in greenhouses in Ipswich and at the Harvard Botanical Garden in Cambridge. When, a short time later, the vine was discovered growing wild in Cambridge, it was assumed it had escaped from the Harvard greenhouse. Since then, it has been a growing bane for gardeners all over the country, one that has boomed since the 1970s. It is now found in every county in the state.

Last year, a group of women in Cambridge who were tired of fighting a losing battle against the weeds in their own yards had an idea.


The problem with black swallow-wort is that it is very good at spreading its seed, which it does by opening up its pods and releasing fluffy, cotton-like parachutes that get carried by the wind. So no matter how much one gardener may weed them out, the fight is useless unless their neighbors also did their part.

“Like a lot of invasive species, they don’t respect property lines,” said Jennifer Forman Orth, a biologist with the state Department of Agricultural Resources, who said the state does not have the resources to battle well-established invasive species, and instead focuses on keeping out those species that are not yet here.


The “Pod Patrol” was born as a way for neighbors to educate neighbors about the vine and “get the conversation going,” said Helen Snively, one of the Pod Patrol founders. “The important thing was to get people to start noticing the plants, to train their eyes.”

The weeds, which are often referred to as the black dog-strangling vine, are easy to not notice because they are ubiquitous. They thrive in the urban environment, where they grow well in disturbed soil and have found their soul mate in the chain-link fences they love to climb.

The mission of the “Pod Patrol” is to pull the pods off the vines before they open and spread seeds. It’s not the most effective method of control – unless you pull the entire root out in the early spring, it will grow back — but the thought was that it was at least something, and that there would be less pushback from neighbors if they were just picking the pods from fences, instead of pulling it out by the roots.

Some people like the aesthetics of the vines, find their star-shaped purple flowers and chili pepper-like pods to be more pleasant than the fences they are obscuring.

“It’s poor-man’s ivy,” said Elizabeth Bolton, a Cambridge realtor who discovered black swallow-wort in her yard a few years ago and quickly transformed into a “guerrilla pod person,” harvesting bags and bags full of the pods wherever she found them. “I very openly hate it,” she says. “And if people knew what it was, I think they would hate it too.”


The Pod Patrol has organized “weedout” events at the Fresh Pond Reservation, set up shop in the local library to educate the public about how to dispose of it (in plastic bags in the trash, not in compost or yard waste where it will resprout), distributed “Pick your pods!” buttons to children, and hung educational fliers on the doors of homes that have an infestation.

They have also tried the “think of the butterflies” approach: If a monarch butterfly mistakes the black swallow-wort for actual milkweed and lays its eggs on the plant, the eggs will not hatch.

Deb Albenberg, who handles the invasive plant management at the Fresh Pond Reservation for the Cambridge Water Department — the pond is part of the city’s drinking water supply — said the Pod Patrol is born of frustration. As she walked to a fence along the reservation recently, the black swallow-wort was abundant.

“If we get all of it here and no one in the surrounding area is doing it, we’re just treading water,” she said. “When you’re dealing with invasive plants, eradication is not a realistic goal. The goal is to keep it from getting worse.”

David Morimoto, a biology professor at Lesley University in Cambridge, has had students do environmental field research on the plants in the past to study urban ecology — Albenberg was one of his students — and said the goal is to get students to notice the ground under their feet.


“These kinds of species are the second-biggest threat to biodiversity on the planet next to habitat destruction,” he said. “The first step is to make people aware.”

But referring to a species as “invasive” in an urban setting is a controversial subject in academia, because there is nothing natural about cities and suburbs, where the most invasive of species is humans.

“In an urban context, there’s really no such thing as a native species because the environment has been so drastically altered,” said Peter Del Tredici, the author of “Wild Urban Plants of the Northeast: A Field Guide,” and a senior research scientist at the Arnold Arboretum, which has been fighting its own battle with black swallow-wort for years.

And while he applauds the effort of the Pod Patrol, he fears the warriors fighting a battle they can’t win.

“Wanting to do something positive for the environment is a noble idea, but it’s not realistic,” Del Tredici said. “This is a biological phenomenon that is very complicated, and well established. It doesn’t matter how vigorous you are, the seeds are going to blow in from somewhere else. Pulling the pod off it does nothing. You can keep your own property neat and free of swallow-wort, but we’re never going to get rid of it. It’s here to stay.”

With all this, though, the Pod Patrol says it will not be deterred.

“I personally think that every pod you pick is a good thing,” said Bolton. “There’s no question it’s depressing when you see how much of it is around, but that’s not enough reason not to try to do something.”


Billy Baker can be reached at Follow him on Twitter @billy_baker.