Garlic Mustard

Description

Garlic mustard (Alliaria petiolata) is an invasive biennial plant native to Europe that was introduced to North America in the 1800s as an edible herb and medicinal plant. It can form dense populations in forests and other natural areas, where it crowds out native vegetation, including species at risk. Garlic mustard can also release chemicals that interfere with the growth of nearby plants and beneficial soil fungi, altering forest ecosystems. A single plant can produce thousands of seeds, allowing infestations to spread and persist for many years.

  • Scientific name: Alliaria petiolata 

  • French name: Alliaire officinale

  • Common name(s): Garlic mustard, Hedge garlic

  • Distribution: Found in British Columbia, Alberta, Ontario, Quebec, New Brunswick, Nova Scotia and Prince Edward Island.   

  • Regulatory Status: Garlic mustard is not a federally regulated species. However, it is regulated as a noxious weed or prohibited weed in British Columbia, Alberta, Saskatchewan, and Manitoba. 

Image of Garlic Mustard

© Quinten Wiegersma via iNaturalist.org, used under CC-BY

Introduction and Spread

Garlic mustard is native to Europe and was introduced to North America in the early 1800s as an edible herb and medicinal plant. It was first recorded in the US in 1868 and in Canada in 1897.  It spreads exclusively via seeds and dense stands can produce more than 60, 000 seeds per square meter. They are typically spread long distances by animals and humans as most seeds fall close to the parent plant. For example, garlic mustard seeds may stick to the bottom of hiking boots and be spread down trails. 

Habitat

Garlic mustard can grow in a wide variety of habitats. It is commonly found in disturbed areas such as along roadsides, trails, fence lines and forest edges. From here, it can spread into areas of high ecological value such as old growth forests. It can tolerate many soil types in addition to light regimes, but is most often found in damp, calcareous-based (limestone) soils in partial shade.

Identification

Note: Garlic mustard has a biennial life cycle which occurs over two years. First and second year plants have different ID characteristics. 

First-year plants

  • Height and Stem: Grows as a circular structure of leaves called a basal rosette.  

  • Leaves: Dark green kidney-shaped leaves with scalloped edges. Distinctive garlic smell when crushed. 

  • Flowers: Does not flower.

  • Fruits: Does not produce fruits.

  • Roots: Slender “S” or “J” shaped taproot.

Second-year plants

  • Height and Stem: Grows an erect stem and up to 1 m tall. The stem is covered in fine hairs. 

  • Leaves: The leaves occur alternate along the stem. They are medium green, triangular with coarsely toothed margins. 

  • Flowers: Flowers occur in umbels (umbrella-shaped flower cluster) and are present April to June. They are small, white and four-petaled. 

  • Fruits:  Fruits are seed pods (siliques) that measure 2.5 cm – 6 cm long and contain 10 – 20 seed. Present from late June into Fall.

  • Roots: Slender “S” or “J” shaped taproot.

Image of garlic mustard flower

Second-year flower

Image of garlic mustard leaf

Second-year leaf

Image of first-year garlic mustard

First-year plant

Impacts

  • Garlic mustard can invade areas of high ecological value such as old growth forests where it can displace native species. This includes species at risk. For example, in Ontario, garlic mustard threatens American ginseng (Panax quinquefolius), drooping trillium (Trillium flexipes), Eastern false rue-anemone (Enemion biternatum), hoary mountain mint and wood poppy (Stylophorum diphyllum) (Meekins and McCarthy 1999; Nuzzo 1999).  

  • Garlic mustard is allelopathic and produces chemicals that inhibit the growth of nearby plants. It also interferes with the growth of arbuscular mycorrhizal fungi (AMF) that assist plants and trees with nutrient and water absorption into their roots. The loss of AMF can change the forest ecosystem by inhibiting the growth of native plants and trees (McCarthy and Hanson 1998; Burke 2008).   

  • Garlic mustard leaves have high nutrient content which can affect nutrient cycling in forests. In particular, it accelerates the rate of decay of native leaf litter which can alter decomposition cycles (Rodgers et al. 2008). This can change the structure and function of forest ecosystems.  

  • Garlic mustard is a host to several viruses that can impact horticulture plants and crops, including: cucumber mosaic virus (Cucumovirus CMV), cabbage black ringspot virus (Potyvirus rapae), and turnip mosaic virus. 

  • When this plant invades pastures of dairy cows, who then consume the plant, they can start producing garlic-flavoured milk which is unappealing to buyers.  

Life cycle

Garlic mustard begins to grow early in the spring and its leaves will often be green under the snow. This gives it a competitive advantage because it is able to start growing earlier than many native species. Garlic mustard has a biennial life cycle that occurs over two years. In its first year, the plant grows low to the ground in a circular structure of leaves called a basal rosette and does not flowers. In its second year, it will produce an erect stem and flower in the spring into the summer (April to June). Flowers produce seed pods (siliques) are produced in summer (late June) and continues into the fall. Once a garlic mustard plant flowers, it dies and a new plant germinates from seed. One plant can produce up to 8000 seeds. Plants can resprout from the root crown or can produce multiple flower heads after being cut (Cavers et al. 1979). 

What You Can Do

You can help prevent the spread of garlic mustard by:

  • PlayCleanGo: To prevent the spread of invasive species, stay on designated trails to prevent spreading, clean equipment, vehicles and clothing after visiting infested areas, and dispose of plant material properly. Cleaning equipment and vehicles that have come into contact with garlic mustard, and educating the public about the importance of not moving plant materials, can help prevent the spread to new areas. 

  • PlantWise: Do not plant garlic mustard or other invasive species. Choose native or non-invasive alternatives. Dispose of yard waste properly and do not dump it into natural areas.

  • Educate: Learn to identify garlic mustard and spread awareness about the ecological risks posed by invasive species and encourage responsible practices in your community.  

  • Reporting: Report garlic mustard and any invasive species to the appropriate provincial authorities such as provincial invasive species councils or report using free tools such as EDDMapS and iNaturalist.  

  • Community Stewardship: Use the Garlic Mustard Best Management Practice Guide to safely and effectively remove garlic mustard from your yard or local green spaces.

Other Resources

  1. Burke DJ. 2008. Effects of Alliaria petiolata (Garlic Mustard; Brassicaceae) on mycorrhizal colonization and community structure in three herbaceous plants in a mixed deciduous forest. American Journal of Botany 95(11): 1416-1425. 
  2. Cavers PB, Heagy MI, Kokron RF. 1979. The Biology of Canadian Weeds. 35. Alliaria petiolata (M. Bieb.) Cavara and Grande. Canadian Journal of Plant Science 59: 217-22. 
  3. McCarthy BC and Hanson SL. 1998. An assessment of the allelopathic potential of the invasive weed Alliaria petiolata (Brassicaceae). Castanea 63(1): 68-73. 
  4. Meekins JF and McCarthy BC. 1999. Competitive ability of Alliaria petiolata (Garlic Mustard, Brassicaceae), an invasive, nonindigenous forest herb. International Journal of Plant Science 160(4): 743- 752.  
  5. Nuzzo V. 1999. Invasion Pattern of the herb garlic mustard (Alliaria petiolata) in high quality forests. Biological Invasions 1: 169-179. 
  6. Rodgers VL, Wolfe BE, Werden LK, Finzi AC. 2008. The invasive species Alliaria petiolata (garlic mustard) increases soil nutrient availability in northern hardwood-conifer forests. Oecologia 157: 459-471. 

Invasive Species Categories

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