What is Garlic Mustard?
Garlic Mustard (Alliaria petiolata) is an herbaceous biannual plant in the Brassicaceae (Mustard) family. It is native to the temperate forests and Mediterranean shrublands of western Eurasia and northern Africa. Leaves are typically around 12 cm long and 8 cm broad, ranging from triangular to heart-shaped (cordate). The margins of leaves consist of large, rounded teeth. When crushed, the foliage emits a garlic-like odour, giving the species it’s common name.
Seeds of Garlic Mustard germinate in the spring, typically in March or April. These young plants will grow into dense rosettes of foliage, up to around 20 cm in diameter by the autumn. They are evergreen, though the rosettes will often appear flattened during the cold winter months when the average temperature is below freezing. In the spring of the 2nd year, Garlic Mustard grows rapidly, generating a flowering stalk up to 1 m tall, although they are typically shorter. Flowers open by May, each consisting of 4 white petals 0.5 cm long. Since there are dozens of flowers per stalk, Garlic Mustard creates quite a showy display! After pollination, 5 cm fruit capsules develop. Each plant can produce hundreds of seeds in ideal conditions, which typically disperse up to a few meters from the parent plant, although some can travel much further.
How was Garlic Mustard introduced to Long Point?
Garlic Mustard was first introduced to North America by European settlers as a culinary, medicinal, and horticultural plant. Considering its high reproductive rate, Garlic Mustard soon escaped from cultivation and spread throughout most of temperate North America, except for the boreal forests (where the growing season is too short), arid areas (which are too dry), and the subtropical forests surrounding the Gulf of Mexico, such as those in Florida and Louisiana. The preferred habitat of Garlic Mustard are open-canopy deciduous forests with high disturbance – this is the location where garlic mustard will reach its highest concentrations. Garlic Mustard can also reach high densities in oak savannas, and closed-canopy deciduous forests, though it is usually mixed with native wildflowers. In locations where Garlic Mustard is well-established, populations can fluctuate year to year, though densities typically remain high. It is intolerant of flooded conditions and thus not usually found in large swamps except in raised areas. While Garlic Mustard effectively spreads naturally through its introduced range, it is often aided by humans. Seeds can attach to footwear and vehicles – allowing Garlic Mustard to spread long distances. It is also spread accidentally through the horticultural and agricultural trade. Port cities and roadways often host major concentrations of Garlic Mustard and other invasive species; monitoring along these entry-points to determine novel occurrences of invasives is good conservation practice.
How does Garlic Mustard impact the environment?
Garlic Mustard reduces resources for native wildlife (through decreasing the abundances of many native plant species) – the reason many conservation biologists and land managers favour its removal. Garlic Mustard is allelopathic – releasing chemicals into the soil that disrupt the normal growth of native plants. Effects include inhibiting seed germination, altering soil microbial composition, disrupting the functions of mycorrhizal fungi. The impacts of Garlic Mustard on native plant communities have wide-reaching effects on wildlife dependant on native plants. Some insects, such as the West Virginia White Butterfly (Pieris virginiensis), mistake Garlic Mustard for closely related native Cardamine species, laying eggs both species. Larvae hatched on Garlic Mustard are unable to survive, as they are not resistant to the defensive, anti-herbivore phytochemicals produced by in Garlic Mustard. Thus, the presence of Garlic Mustard increases larval mortality for these species. In addition to allopathy, the presence of Garlic Mustard raises soil pH, and influences the nitrogen cycle, which may be partially attributable to altered microbial composition in soils. Dying Garlic Mustard plants promote the establishment of these decomposers, increasing the efficiency of N-cycling enzymes, which in turn generates higher nitrogen mineralization rates, and nitrification rates (Edwards et al., 2022).
How is Garlic Mustard controlled?
Land conservancies, including Long Point Basin Land Trust, frequently remove Garlic Mustard on their nature reserves annually as part of spring land stewardship activities.
To effectively control Garlic Mustard:
- Plants need to be completely removed and properly disposed of – any remaining plant material has potential of re-establishing, undermining Garlic Mustard control efforts
- Removal procedures need to be repeated for multiple years to observe noticeable declines in Garlic Mustard densities, as Garlic Mustard seeds can remain viable for up to 15 years
- Control efforts must encompass all Garlic Mustard plants within a site to prevent re-establishment through dispersal
There are several different methods of removal, such as physical removal (hand-pulling), chemical removal (herbicide application), and biological control (introduction of the natural predators of Garlic Mustard). Currently, physical and chemical methods are most widely utilized, though biological control may become more important if herbivorous insects are released. Most biocontrol efforts focus on two seed-eating weevils, Ceutorhynchus scrobicollis (federally approved for release in 2018), and Ceutorhynchus constrictus (approved in 2025). Time will tell whether biological control efforts will substantially reduce Garlic Mustard densities – but in the meantime, the continued removal of Garlic Mustard remains a relevant and much-needed conservation practice in areas where the plant is established.
Garlic Mustard is Edible
Did you know that Garlic Mustard is edible? Garlic Mustard can be used as a leafy green, providing a nutritious source of calcium, iron, manganese, and zinc. It also contains substantial quantities of Vitamin A, C, and E, as well as a healthy dose of fibre! The plant is gaining popularity as a wild food, especially since it is prolific as an invasive plant species – there’s no shortage! The garlic-like flavour of the leaves allows Garlic Mustard to be utilized as a pesto or a salad. If you plan on using Garlic Mustard for culinary purposes, be sure to properly identify the plant – there are many toxic woodland plants that resemble Garlic Mustard.
Written by: Matthew Palarchio – HBSc, Environmental Sciences, Western University
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References
Coles, W. (2025, March 31). Nearly 25 years of research precedes release of seed-feeding weevil to fight garlic mustard in North America. Invasive Species Blog. https://blog.invasive-species.org/2025/03/31/nearly-25-years-of-research-precedes-release-of-seed-feeding-weevil-to-fight-garlic-mustard-in-north-america/
Edwards, J. D., Cook, A. M., Yannarell, A. C., & Yang, W. H. (2022). Accelerated gross nitrogen cycling following garlic mustard invasion is linked with abiotic and biotic ch0anges to soils. *Frontiers in Forests and Global Change*, *5*, 1050542. https://doi.org/10.3389/ffgc.2022.1050542
Nature Conservancy of Canada (n.d.). Garlic Mustard. https://www.natureconservancy.ca/en/what-we-do/resource-centre/invasive-species/garlic-mustard.html
Photo Credits
Small Rosette © Kristin Piston
Large Rosette © Ian Whyte
Flowers © CWF-Meagan
Group of Plants © Matthew Palarchio
