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Garlic mustard (Alliaria petiolata) is likely the number one invasive plant species threatening Ontario’s forested landscapes today. It can be found in many places, including right here in the city of Waterloo. Removal of this plant from your property is strongly recommended to prevent further encroaching! Here is some information to get you started.

How can it be Identified?

This biennial plant starts out in its first year as a very tiny plant that eventually develops a rosette of kidney-shaped leaves. It sort of looks like a violet, except mainly for its long taproot. The plant remains green through the winter, allowing an early start in the spring (photo 1 below).

The mature second year plant can grow as much as 3 to 4 feet tall. It has triangular, alternate, sharply toothed leaves and produces masses of small white flowers with 4 petals followed by seed pods which are long, thin, and green, turning brown at maturity (photo 2 below).

First year Garlic Mustard

Photo 1: First year Garlic Mustard plant. Photo courtesy of Christine Hanrahan and the Fletcher Wildlife Garden. Click photo to enlarge

Mature Garlic Mustard plant

Photo 2: Mature Garlic Mustard plant. Photo courtesy of Christine Hanrahan and the Fletcher Wildlife Garden. Click photo to enlarge

What is the Best Way of Removal?

Start by removing small satellite populations (i.e. with just a few plants) to help prevent the plant from spreading. Then tackle larger more established areas. Focus on the mature, second year plants, as the majority of first-year plants do not mature. For these more established areas, note that long-term commitment is necessary as the seed pods can last a long time (up to five years or more) in the soil!

Pulling by hand from the root is most effective since plants can sprout again from cut stems and even roots. Note that seeds may become dislodged from the plant and become established in the soil while pulling. Consequently, it is best for hand-pulling to be done prior to flowering.

For large plant populations where garlic mustard has completely choked out all native plants, you may alternatively wish to use a hand-held motorized trimmer to cut the plant. You should do this twice a year prior to flowering and repeat, or hand pull, until no new plants appear.

Be sure to remove any pulled-out stalks! These contain toxins and may already have seeds or enough food reserves in them to allow the seed pods to grow and ripen. When removing the plants, put them in Yard Waste Bags for pickup. The high temperature municipal compost system will ensure destruction of the seed pods.

Why is Garlic Mustard so Good at Spreading?

Garlic mustard is an extremely prolific plant that produces many seeds. The seeds can reside in the soil for at least five years if not longer. It also produces a chemical substance (called an “allelochemical”) that prevents the growth of plants and saplings, and stunts the growth of small trees and shrubs as well as even larger trees. What is more, garlic mustard has no significant natural enemies in North America.

Why Is There So Much Concern?

Garlic Mustard Field

Photo 3: Established population of Garlic Mustard. Photo courtesy of Christine Hanrahan and the Fletcher Wildlife Garden. Click photo to enlarge

Because garlic mustard is so good at spreading, it is extremely efficient at pushing out other plant species (as shown in photo 3). For maintained property, this can be a particular concern in gardens, where the fact that the ground is not mowed means that garlic mustard can quickly overrun other plants.

In natural areas, the plant gets established more easily in disturbed areas like along trails, but can also invade largely pristine, undisturbed areas. This means not only a loss in the variety (or biodiversity) of other plant species, but drastic changes for other animals living there as well. For instance, garlic mustard appears to alter habitat quality for several species of salamanders through changes in forest litter layer depth and composition.

What Else Can I Do?

Garlic mustard does not know any boundaries and so spreads both on private and public property. There may be public spaces in your neighbourhood that you can get involved in garlic mustard removal. To find out more, contact the City of Waterloo at (519) 886-1550. Mention that you would like to get involved with the Partners in Park Program for the management of garlic mustard.

Further Resources

Have More Questions?

Feel free to email Volunteers working in the community will be happy to answer your questions.


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