Invasive of the Month: Garlic Mustard (Alliaria Petiolata)

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Find it

Garlic mustard is a small green invasive plant with leaves that smell like garlic when crushed. It’s an unusual invasive because almost anyone, regardless of age, ability or tool readiness, can pull garlic mustard plants. March and April are great times to take action on garlic mustard, before it forms flowers and seeds.

Garlic mustard is often found in forests and at forest edges. It needs moist, non-acidic soil, and is very tolerant of shade. During winter, garlic mustard plants from the previous year are visible as small clumps of 1-inch leaves that remain green and low and limp, flattened against the ground. With longer, warmer days, they perk up and becomes green mounds of roundish leaves. Around May, they bolt upwards with white flowers on a stalk a foot or two high. After the flowers, seeds form in pods up and down the stalk. In late summer, the pods dry and burst open, releasing hundreds of seeds.

Why it’s a problem

Native to Europe, garlic mustard now ranges across the northern half of the nation. It’s an aggressive invader and takes over in several ways. No native insects or animals eat it. Because deer don’t like it, they make more room for it when they graze other plants. Its roots produce chemicals (allelopathic compounds) that are toxic to other plants. As it grows and multiplies, it sucks up resources other plants need. Forests that previously featured spring flowers like trillium or lady slippers can become vast garlic mustard monocultures in a few years.

What to do

Remove it. Gaining control over garlic mustard takes several years because it spreads by seed; the seeds remain viable for five years or more. Spring is the best time to weed out garlic mustard as last year’s plants become more visible but are still small enough to pull up. Grab them at the base to pull up the roots. A small shovel or trowel or a forked root-cutting tool can help. 

Flowers and seeds can continue to ripen on recently pulled plants, so remove them altogether, or pile and cover with black plastic to dry them out. In very early spring, before flowers have begun to form, plants can be left to decay where they are pulled. Repeating this for several years will greatly reduce garlic mustard invasions, allow native plants to survive, and make way for a wider variety of plants over time.

For more information on invasive plants, events and the NOT WANTED campaign, drop us a note on the Granby Conservation Commission webpage.