Look Out For These Invasive Plants in Maine
Keep an eye out for invasive plants in your yard, like the Asiatic Bittersweet or Japanese Barberry, two of the most invasive plants in Maine.
Written by Bonnie Stinson
Reviewed by Melanie Reiff
From the Asiatic bittersweet to common buckthorn and Japanese barberry, these are 10 of the most invasive plant species in Maine.
From gorgeous coastal views to stunning fall foliage, Maine has a lot of natural beauty to draw tourists and homeowners alike. But whether you’re looking to move to Maine or already own a home there, it’s important to keep an eye out for invasive plants that can destroy your property or even risk your home’s value!
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The top 10 invasive plant species in Maine
1. Asiatic bittersweet
Scientific name:Celastrus orbiculatus
What it looks like: Woody vine with slightly elliptical toothy leaves. Greenish-yellow 5-petaled flowers produce bright orange seeds in fall.
Why it’s a problem: Asiatic bittersweet twines around mature trees and even grows through low vegetation strangling most other plants it latches on to. Thickets of Asiatic bittersweet can also harbor large tick populations and transmit diseases that will kill crops and native trees.
What to do: Small plants can be pulled up by the root, but larger established vines will need to be cut aggressively (and often!). Cut vines at chest and ankle height to prevent new vines from climbing the old ones. Chemical herbicides can be used to kill root systems. Leave cut vines in trees to die—pulling the vines out may cause additional harm to the plants (or structures) they’re attached to.
2. Black locust
Scientific name:Robinia pseudoacacia
What it looks like: 40-100’ tall tree with smooth green bark on younger trees and furrowed, dark brown bark as the tree ages. The trunk and branches grow long pairs of spines and the leaves are oval and blue-green and grow in 8-12” shoots.
Why it’s a problem: Black locust trees change the chemistry of the soil they’re growing in to create soil conditions preferable to non-native and invasive species. These soil conditions persist even years after black locust trees have been removed, making it difficult to remove other invasive species.
What to do: Seedlings and saplings can be pulled, but resprouting may occur so watch the area carefully. Larger trees can be cut down, but the stump will need to be treated with herbicide in order to prevent the tree from regrowing.
3. Black swallowwart
Scientific name:Cynanchum louiseae
What it looks like: Thin, twining vine with lance or heart-shaped leaves. Star-shaped purple flowers appear from May-September, and the pollen smells like rotting fruit.
Why it’s a problem: Black swallowwart can form large patches that crowd out native plant species, destroying important insect habitats which in turn impact the feeding habits and nesting areas of native bird species. Black swallowwart also poses a danger to plants like milkweed, which are a necessary food source for endangered Monarch butterfly populations.
What to do: Dig plants up by the root before seed pods form and dispose of them in garbage bags. Do not mow them down as this will encourage aggressive resprouting. For large thickets, chemical herbicide sprays may be necessary.
4. Canada thistle
Scientific name:Cirsium arvense
What it looks like: A creeping herb that grows to 2-5’ tall. Flowers are purple and flask-shaped, and several flowers will sprout on one plant. Leaves are wavy or crinkled and very spiny.
Why it’s a problem: Canada thistle will dominate fields and pastures to crowd out any other desirable plant species. This creates areas with very little plant diversity and disrupts the habitats of several insect and animal species.
What to do: Established plants will need to be mowed, or cut or pulled out by the roots. Whichever method you choose, it may take years of diligent work to completely get rid of Canada thistle. Sheep and goats will eat Canada thistle, so letting them graze in an area is an option to get rid of the plant. If you intend to pull them out, make sure you wear gloves as the leaves are sharp!
5. Common buckthorn
Scientific name: Rhamnus cathartica
What it looks like: Small shrub or tree with almost round leaves. Produces small, glossy black berries in late summer.
Why it’s a problem: Common buckthorn is dense and creates large shady spots under its branches, which kill native plants that happen to be growing underneath it. Its leaves, when they drop and decompose, create high levels of nitrogen that attract invasive species of earthworms which further degrades the soil conditions. Buckthorn can even cause defects and death in some amphibian species.
What to do: Small plants can be pulled up by the root, but larger established shrubs will need to be mowed down. You’ll have to mow common buckthorn frequently throughout the year in order to keep it from resprouting, and it could take years to completely kill an infestation.
MORE: Best places to live in Maine
6. Common reed
Scientific name:Phragmites australis
What it looks like: Very tall grass that grows in dense clusters. Leaves are yellow to greenish blue and are widest in the middle and taper at the tip. Common reed produces fluffy seed heads during the fall, and a bare woody stalk will remain in the winter.
Why it’s a problem: Increased leaf litter from common reed can reduce fish populations in wetlands and marsh areas. They also decrease nesting habitats for turtles, including the endangered Blanding’s turtle. Common reed can cross-pollinate with other plant types to create hybrid species which reduce the populations of native plant species.
What to do: Small patches of common reed can be mowed repeatedly during the year, with a controlled burn in the spring to remove old thatch and encourage native plant growth.
7. Garlic mustard
Scientific name:Alliaria petiolata
What it looks like: Young plants start as small rosettes with toothy, kidney-shaped leaves while older plants will grow up to 3’ and have more triangular leaves. Leaves smell like garlic when crushed.
Why it’s a problem: Garlic mustard sprouts very early in the growing season and is well-established before many native species. This means that when native plants are ready to grow, they’ve already lost out on space, sunshine, and nutrients from the soil.
What to do: Garlic mustard is edible, and younger plants are easy to hand pull from the soil. Older plants need to be bagged after they’re pulled to prevent seeds from spreading. You can also mow large patches of garlic mustard, but be prepared to mow them often before they completely die out.
8. Glossy buckthorn
Scientific name:Frangula alnus
What it looks like: Shrub that can grow to 20’, the glossy buckthorn has glossy elliptical leaves and produces red or dark purple berries in late fall.
Why it’s a problem: Glossy buckthorn competes with native plant species for resources, especially among low-growing plants. Glossy buckthorn is especially dangerous in white pine forests where its thick and wide-spread root system strangles young pine tree seedlings before they can grow. Glossy buckthorn is also a host for the fungus that causes oat rust disease.
What to do: Smaller plants can be pulled up by the roots, but larger plants will need to be mowed down repeatedly to discourage resprouting. You can also apply herbicides to the buckthorn stump after it’s cut to prevent regrowth.
9. Goutweed
Scientific name:Aegopodium podagraria
What it looks like: Also known as Bishop’s weed, goutweed is 1-2’ feet tall and spreads along the ground. Leaves are serrated and grow in groups of three. Goutweed produces tiny white flower clusters that appear on 2-3’ stalks.
Why it’s a problem: Goutweed changes the chemistry of the soil it grows in along with raising the humidity near the ground. This smothers native plants, especially tree seedlings like the white pine, black spruce, and balsam fir.
What to do: Pulling the plants out by hand will not remove its root system. Plants need to be dug up to remove the roots completely, then disposed of in a bag to prevent reseeding. It may take repeated diggings before the goutweed is wiped out completely.
10. Japanese barberry
Scientific name:Berberis thunbergii
What it looks like: Shrubs that can grow 6’ tall and wide with sharp spines on the branches. Leaves are round at the end and taper toward the branch. Red berries appear in the late summer.
Why it’s a problem: Japanese barberry changes the composition of the soil it grows in which can kill native plants and create a habitat where only more Japanese barberry can survive. The shrub is also a habitat for disease-carrying ticks that can cause health issues for humans, native animals, and livestock.
What to do: You can pull small plants up by hand, but wear gloves to avoid the spines! You can mow larger plants, or conduct a controlled burn, but these methods will need to be repeated to ensure that the infestation is taken care of.
MORE: Maine renters insurance
How to save on homeowners’ insurance in Maine
The invasive plants on this list not only threaten the natural habitats and plant diversity in Maine’s forests and wetlands, but they can also be a hassle for homeowners trying to get them out of their yard or property.
Fortunately, finding affordable homeowners insurance in Maine isn’t a hassle. With a little help from
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