Invasive Plants
Identification and removal of invasives in Maine
Invasive plants pose a serious threat to park ecosystems. As a nonprofit whose mission is to enhance the vibrant parks of Portland, ME, we are committed to addressing this threat. City staff work diligently to remove invasive plants from parks, but this is an ongoing battle that can benefit from any extra help.
That’s where Portland Parks Conservancy comes in: our volunteers remove invasive plants from the city’s parks, providing much needed aid. We host events doing this important work throughout the summer and fall – anyone interested in protecting Maine’s environment is welcome to join!
Learn how to identify and safely remove invasive plants below. We always encourage attempting to remove invasives by physical means before considering herbicide.
Photos: Mid Michigan CISMA
Swallowwort
Cynanchum louiseae (black swallowwort)
Cynanchum rossicum (pale swallowwort – extremely uncommon in Maine)
Swallowwort is a vine that is identified by its shiny dark leaves and tiny brown flowers that bloom in the spring and summer. Pull out the vine and as much of the roots as possible.
Swallowwort spreads via dandelion-like seeds that pop out of seed pods which resemble green beans. To prevent spreading, harvest the pods in late July or early August and either throw them out or burn them.
Photos: James H. Miller (USDA Forest Service, Bugwood.org), Maine Department of Agriculture, Conservation, and Forestry
Bittersweet
Celastrus orbiculatus
In the winter, bittersweet is easy to identify by its bright red berries and its exposed vines
Cut the vine 1-3 feet off of the ground, then cut again 6 inches up the vine, leaving a 6inch gap in the vine. You may need hand clippers or a small saw, depending on how thick the vine has become. For more successful results, spray herbicide on the two cut sites. The vines in a tree should break off over time on its own as the tree grows.
Asiatic bittersweet (invasive) can be confused for American bittersweet (native). However, American bittersweet is uncommon in Maine.
Photos: Leslie J. Mehrhoff (University of Connecticut, Bugwood.org)
Knot Weed
Reynoutria japonica (also known as Fallopia japonica or Polygonum cuspidatum)
Pull the plant up by the base to ensure that you have removed its roots from the ground. If this is too challenging for larger plants, first cut down the bamboo-like shoots then spray with organic herbicide (do not spray other plants! It will kill them). Wait 7 days and then pull up plants by the root.
Photos: Master Gardeners of Northern Virginia, Hilton Pond Center
Multi-flora Rose
Rosa multiflora
Wear gloves to protect your hands from thorns. Proceed to pull out vines one or two at a time. It should pull out in clumps, though you may need hand clippers to get it started. Pull out as much as you can before mowing it down. Mow the area 3-6 times per season to prevent the plant from growing. Repeated mowing will deplete the plant's food stores and kill it over time.
Photos: Sophia Cameron (National Parks Service), Erin O’Connell (University of Minnesota)
Glossy Buckthorn
Frangula alnus
Cut the shrub down to a stump less than 6 inches off of the ground. Cover the stump with a black plastic bag or a tin can. Glossy buckthorn is shade tolerant, so it is necessary to use an opaque material. It may take a year or two, but this method will kill the plant and prevent growing while it does.
Photos: Leslie J. Mehrhoff (University of Connecticut, Bugwood.org)
Honeysuckle
Lonicera morrowii (Morrow’s Honeysuckle – white flowers)
Lonicera tatarica (Tatarian Honeysuckle – pink flowers)
Use a lopper or a hand saw to cut the base of each stem of the plant. Once completed, you can choose to use a few drops of organic herbicide locally on each cut stem. It is recommended to add food coloring to the herbicide so that you can see where the chemicals are being distributed.