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Plantings in City Spaces: Information on Natives Policy & Invasive Plants

The City of Somerville Parks & Open Space and Urban Forestry (UF) divisions consider many factors when developing urban spaces. We prohibit the use of invasive plants and would like your help removing them. There are many factors that go into choosing the right plant for the right space, including but not limited to: the challenges of urban conditions, management of urban plantings, the need to consider and plan for climate change, and the desire to achieve a balanced approach while encouraging plant diversity and resilience.

Contact Information

Unwanted Plants

The Urban Forestry Committee is in the process of updating the Somerville's Most Un-Wanted Weeds list, and is asking for help in gathering local photos that are representative of invasive plants (non-native plants that are harmful to the environment and the most problematic "weed" species). Please submit your good quality photos to:

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Somerville's Most
UN-Wanted Plants

Click here for a printable PDF.

Please note: This list was compiled to assist non-gardeners/volunteers who are working within City-led work days in identifying non-intentional plants in our parks. It is not comprehensive, nor is it a value judgment about which plants are weeds or not, or their ecological value. 

Black swallow wort



Field Bindweed

Green Foxtail

Japanese Knotweed

Pennsylvania Smartweed

Quack Grass

Sow Thistle

Canada Thistle

Common Burdock


Garlic Mustard


Norway Maple Seedling

Purple Clover

Shepherd's Purse

Annual Fleabane

Sources: Canadian Thistle (left): (CC BY-SA 2.0) F.D. Richards via Flickr; Chickweed (left): (CC BY 2.0) Simon via Flickr; Chickweed (right): (CC BY-SA 4.0) Lazaregagnidze via Wikimedia Commons; Common Burdock: (CC BY 2.0) Homer Edward Price via Flickr; Dandelion © 2010 (CC BY 2.0) Rev Stan via Flickr; Dead-nettle (right): (CC BY-SA 2.0) hadera.baltica via Flickr; Garlic Mustard (right): (CC BY 2.0) Katja Schulz via Flickr; Green Foxtail: (CC BY-SA 2.0) Matt Lavin via Flickr; Horseweed (left): (CC BY 2.0) Jim Kennedy via Flickr; Horseweed (right): (CC BY-SA 2.0) F.D. Richards via Flickr; Japanese Knotweed: (CC BY-SA 2.0) Gordon Joly via Flickr; Norway Maple Seedling (left): (CC BY 2.0) Gilles Gonthier via Wikimedia Commons; Pennsylvania Smartweed (left): (CC BY-SA 2.0) F.D. Richards via Flickr (left): (CC BY 2.0) Phil Sellens; Swallow-wort: (CC BY-SA 3.0 (left), CC BY-SA 4.0 (right)) R.A. Nonenmacher via Wikimedia Commons; Emerald Ash Borer: David Cappaert, Michigan State University

Native Plants Ordinance

Help Eradicate Black Swallow Wort

The City of Somerville is partnering with community groups to raise awareness about black swallow-wort (BSW), a very aggressive and invasive, non-native weed that can be found throughout Somerville. It displaces native plants and habitats, threatens butterflies and songbirds, and is toxic to deer and livestock. BSW is especially harmful to the monarch butterfly population as BSW resembles milkweed, where monarchs lay their eggs, and once the monarch larvae hatch they die from eating the toxic BSW leaves.

BSW pods have already started to appear in Somerville this season, and the City and community groups are asking community members to remove BSW when they see it. Volunteers are also being sought to help distribute informational door hangers in their neighborhoods about BSW, how to identify it, how to and remove it. 

The BSW plant has shiny, green leaves that come in pairs along winding vines that are often found around fences and shrubs. It also has slim, green pods that appear in June, which are imperative to remove before they turn brown and disperse wind-borne seeds. BSW also has small, dark purple flowers that grow in clusters with five petals and a green center. Whenever possible BSW should be uprooted completely and the pods should be removed. To dispose of the plant, be sure to place all of it in a sealed trash bag. Do not compost or place BSW in paper or yard waste bags, they will resprout.

To pick up door hangers now through mid-July, please visit the Somerville Central Library at 79 Highland for contactless pickup. Because there is a limited quantity, we ask that each person take a maximum of  20 door hangers.

Thank you for helping eradicate this invasive species!

How to Identify and Remove Black Swallow Wort

Other Un-Wanted Plants in Somerville

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