The problem

Garlic Mustard (Alliaria petiolata) is a shade-tolerant biennial plant that thrives in woodland settings. It is considered a serious invasive pest of natural areas, particularly woodlands, displacing native flora and severely reducing species diversity. Its aggressive, rapid growth allows it to form dense carpets that prohibit growth of other species.

Recent research shows that Garlic Mustard can release chemicals that destroy the mycorrhizal fungi that many trees depend on for nutrients. When Garlic Mustard invades a site, growth of tree seedlings is reduced. Like many non-native plants, Garlic Mustard has few natural enemies to help keep it in check.

Garlic Mustard at the FWG

Garlic Mustard grows mainly in the Old Woodlot at the FWG, although in recent years we’ve found patches in our Old Field habitat and at the end of our Amphibian Pond.

Control strategy

Our control strategy is based on the fact that this plant is a biennial, so preventing seed production should eventually eliminate it. We spend several weeks in May pulling out plants that are blooming. During the summer, our student volunteers monitor the various patches for later blooming plants and any others that we missed in spring.

Seed pods

Strategy promoted by the Stewardship Network

  • Prevent new seedset and deplete existing seedbank (see photo of seed pods at right)
  • Focus on rosettes, not seedlings (the rosettes are the plants that are going to bloom this year and produce seeds, so it’s important to remove them; the thousands of tiny seedlings can be ignored temporarily because most of them will not survive to the next year)
  • Focus on satellite infestations (start with outlying populations, then work back to the heavier infestation at the core; if you start at the core, you might track seeds out to uninfested areas)
  • Check cleared areas later in the season and in subsequent years, as seeds may live in the soil for many years before germinating and creating a new infestation

Plants are bagged and removed from the site. In previous years, we left pulled plants on the ground assuming that they would not be able to develop to the point of producing seed. We now know that this is not true, and ALL plants must be removed from the site.

Recognizing Garlic Mustard in spring

Garlic Mustard is one of the first plants to come up in the spring. Rosettes appear around the same time as trilliums and other early spring wildflowers. We’ve found it helps to get an early start on weeding, but it’s easy to confuse small Garlic Mustard plants with other species.

Here are photos of all the rosette-type plants growing in our woodlot in early May. Garlic Mustard is the only real invasive. Motherwort is not native and we usually weed it out as well, but so far it hasn’t spread as aggressively as Garlic Mustard.

Garlic Mustard
(white flowers on tall stem)

(mauve flowers on tall stem)

Rough Avens
(yellow flowers)

(low, blue-violet flowers)

(white flowers on short upright stems)

Barren Strawberry
(low, yellow flowers)

More information

  • Ontario Ministry of Natural Resources – Garlic Mustard
  • Environment Canada, Invasive plants of natural habitats in Canada – Garlic Mustard
  • National Park Service, Alien Plant Working Group – Garlic Mustard
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This page was revised 14 July 2022
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