Under Invasion

Invasive species are a problem everywhere, and one I don’t think we talk about enough. Recently I’ve been seeing one old nemesis crop up, and I thought I’d share. The more people are aware of the problems invasive species can cause, the more people can help to limit their spread as much as possible.

Let’s start by making one thing perfectly clear: in a well-balanced ecosystem, everything has its place, no matter how annoying it may be. Things that are invasive in the Northeastern United States have a place of origin where they make a valuable contribution to the overall balance of life. The key word there is balance. Nature generally has checks and balances to keep everything in harmony. Herbivores feed on plant species so they don’t overgrow. Predators keep the herbivore populations from getting out of hand. When a plant or animal is moved from its native area to a new place, the new environment doesn’t have any checks and balances to control it. The new species can badly upset the established harmony.

Today’s example is a plant known as garlic mustard (Alliaria petiolata). This herb is native to Europe and parts of Asia, and is first recorded in North America in 1868 on Long Island. Now, it is found in various areas of the northeast and midwest. It was most likely introduced for its culinary and medicinal uses. It is often found in forest understories, particularly along trails and forest edges, or along roadsides, and it can form dense stands. It is a biennial, and spends its first year as a small rosette of toothed green leaves. In its more recognizable second-year form, it is a tall plant, standing as much as 2-3 feet high and fairly straight, with clusters of small white flowers.

A stand of garlic mustard

A stand of garlic mustard

So, what’s the problem? At first glance it may seem that garlic mustard is just another wildflower, and an edible one at that. In fact, it looks an awful lot like some of our native understory plants, like toothwort, early saxifrage, and sweet cicely. But because it is not a native plant, there are some important differences. Firstly, garlic mustard is able to out-compete the comparable native plants listed above, in part because the major native herbivores like deer don’t feed on it. They will preferentially pick out and eat the others instead. As garlic mustard becomes over-represented in the understory, other imbalances arise. For example, several species of native butterfly typically lay their eggs on plants like toothwort. When toothwort is less available, they lay those eggs on garlic mustard instead. The oils in the leaves of the garlic mustard can interfere with the eggs and keep them from hatching, or be unhealthy to caterpillars trying to eat them. One of these butterflies is the endangered West Virginia white butterfly.

Did you know that plants engage in chemical warfare? It’s true: plants give off chemicals that help them compete with other nearby plants for territory and nutrients. When this back-and-forth of chemical exchanges evolves over long periods, it is just another set of steps in the elaborate dance of the ecosystem. When an imported plant is dropped in the middle of this dance, however, the chemicals it exudes that were perfectly in step with its normal habitat cause havoc instead. Garlic mustard interferes with the beneficial fungi that are important for native tree seedling growth.

What can you do to keep your forest ecosystem healthy? Eradicating garlic mustard is a big job, but every little bit helps. Start by being certain you’ve identified garlic mustard correctly. It’s pretty distinctive, but make sure not to confuse it with the similar native plants mentioned above. The leaves have a heart shape and are toothed around the edges, and are generally pointed at the tips. The first-year rosettes have similar leaves, but more kidney-shaped.


The flowers grow in clusters, usually with an iconic cluster at the top of the plant. Each small blossom will have 4 white petals oriented in the shape of a cross. (The clusters can have more flowers than this, but the specimens around my yard are a little light right now). The long, four-sided seed pods will also start to appear around this time of year.


If in doubt, pluck a few leaves and crush them in your fingers. They should give off a garlic or onion-like smell. This will tell you you’ve got the right plant! Once you’ve identified it, you’ll want to grasp near the root and simply pull it out of the ground. This is easier when the soil is damp. Try to get as much of the root as possible, or it can regrow. Do this every year! Seeds can grow after even as long as five years in the soil. Once the plant is pulled, you need to make sure the seeds don’t go back into the soil. Put it in a burn barrel if you have one, or bag it securely and put it in the garbage. Feel free to use the leaves as a culinary herb, if you know they haven’t been sprayed.

More questions? Want to check out the sources I used to investigate garlic mustard? I first learned about garlic mustard from the Brandywine Conservancy, a local conservation group. Then I did some more research here:





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