By Jim Clark

According to the City of Somerville and specialists in this field, invasive plant species, such as black swallow-wort (BSW), can interfere with monarch butterfly reproduction.

Monarch butterflies help pollinate other plants, so a healthy population is important. If you have black swallow-wort in your yard, now is a good time to get rid of it before its seeds drop.

However, the Somerville UrbanAg Blog emphasize that “not all non-native plants are invasive plants. Invasive plant species are a problem because they interfere with native landscapes as well as the intentional landscapes in our gardens and parks. As the USDA puts it, ‘…not all exotic species are considered harmful. Non-native plants are fundamental to our lifestyle – most of our food crops, such as potatoes and wheat, are not native to the United States. Invasive species, however, are exotic organisms that have gone beyond being useful and have become harmful. There are some benefits to all species – but invasive species do more harm than good.’”

The blog also points out that many invasive plants, such as Japanese barberry or Norway maples are actually illegal to sell in Massachusetts, and the city does not plant invasive species in its parks and open spaces.

In addition, the blog states that though native to Southwestern and Northern Europe, BSW is easy to find in Somerville. A member of the same plant family as the milkweeds native to New England, BSW grows rapidly and aggressively, covering other vegetation and taking over urban fences as well as rural woodlands. BSW is aggressive and harmful in a variety of ways: it releases biochemicals into the soil that prevent the establishment of other plant species. Its seeds are carried on the wind or transported by water; its roots are toxic to some mammals; and, its plants toxic to many insect larvae.

According to the blog post, awareness has grown about BSW in recent years and a number of folks have committed to pulling and properly disposing of the noxious weed.

Both the Somerville Garden Club and the Cambridge Pod Patrol have been working to eradicate BSW.  You can help them by getting involved in their events, pulling BSW in your yard and, if you want to help the monarchs, replacing them with the native milkweeds.

You can find a list of Massachusetts invasive species here: https://www.mass.gov/service-details/invasive-plants.

The full Somerville UrbanAg Blog post can be found at http://somervilleurbanag.tumblr.com/post/177099083348/not-all-non-native-plants-are-invasive-plants.