Garlic Mustard

First year plants

Height: First year garlic mustard is low-growing.

Leaves: First year garlic mustard leaves are dark green and kidney-shaped. They have scalloped margins and deep veins that make the leaves look wrinkled. A strong smell of garlic is present when the leaves are crushed.

Roots: First year garlic mustard roots are slender with a white “S” shaped taproot.

Second year plants

Height: Second year garlic mustard grows up to 1 m in height.

Stem: Second year garlic mustard plants have hairy stems.

Leaves: Second year garlic mustard has alternative, 3-8 cm long, triangular, and coarsely-toothed leaves.

Flower: Second year garlic mustard has white flowers, each with four petals. Second year plants flower in early May.

Fruit (seeds): Second year plants have seed pods that are 2.5-6 cm long, each containing 10-20 small black seeds.

Garlic mustard is widespread in Southern Ontario, from Windsor to Ottawa, and has also be found as far north as Sault Ste. Marie. Canada-wide, garlic mustard has been found in BC, Alberta, Ontario, Quebec, New Brunswick, Nova Scotia, and PEI.

Distribution Map Provided by EDDMapS 

Vegetation communities

Garlic mustard does not appear to require disturbance to become established, making it a threat to mature forests. It can enter, establish itself, and become the dominant plant in the forest understory in 5-7 years. It actively displaces native spring ephemeral wildflowers through direct competition and/or through changes to the soil/leaf litter.

Forest ecosystems and wildlife

Garlic mustard is allelopathic; the chemicals produced in the roots have been shown to prevent the growth of other plants and grasses. These chemicals also affect the growth and regeneration of arbuscular mycorrhizal fungi (AMF), beneficial fungi in the soil that help trees and plants absorb nutrients and water into their roots. The reduced AMF in forests inhibits growth of most native tree seedlings and plants, which depend on AMF. Loss of AMF changes the forest ecosystem. Non-native species are able to grow and displace native seedlings, including those which would eventually become canopy trees such as maples and oaks. This effect can last for years after garlic mustard has been removed. 

Ontario’s forests have evolved to depend on leaf litter, which provides a layer of slowly decomposing organic matter on the forest floor. Garlic mustard leaves have a high nutrient content. When they die, they accelerate the rate of decay of native leaf litter, altering the natural decomposition cycle and changing the structure and function of forest ecosystems.

This effect is compounded by non-native earthworms which have also caused ecosystem changes to Ontario’s forests by reducing the amount of leaf litter available. Garlic mustard is able to establish itself in these low-leaf litter environments, whereas many native species cannot. By changing the composition of the litter layer on the forest floor, garlic mustard reduces habitat for ground-nesting birds and affects habitat for salamanders and other forest floor-dwelling animals.

Mechanical Control

Hand pulling: Hand pulling is a viable strategy for small populations or few plants. Hand pulling garlic mustard will create soil disturbance, which stimulates the germination of seeds in the seed bank. The entire “S” shaped root must be removed to avoid resprouting from buds on the root system. Hand pulling must be repeated more than once and is more likely to be successful when followed with replanting with native species.

Basal cutting/mowing: Basal cutting involves cutting 2nd year plants at the base of the stem. The best time to do basal cutting is just after the plants flower and before they produce seeds. Garlic mustard plants can flower at different times, so it may need to be repeated more than once in a season. Basal cutting is preferable to hand pulling because it reduces the soil disturbance. Plants that have been mowed can still send up flowering stalks, but continuous mowing throughout the growing season can prevent seed production.

Clipping flower heads: Clipping the flower heads will prevent seed production but must be repeated continually until the end of the growing season, as it encourages new flowers to emerge.

Chemical Control

For more information on chemical control see the Best Management Practice on Garlic Mustard (below).

Learn how to identify garlic mustard and other invasive plants, and how to effectively manage these species on your property. See The Landowner’s Guide to Controlling Invasive Woodland Plants. Go to ontario.ca/invasivespecies, click on Here’s a list of things you can do to help fight invasive species, and click on the title (Garlic Mustard MNR):

• Avoid using invasive plants in gardens and landscaping.
• Buy native or non-invasive plants from reputable garden suppliers. Native plants provide habitat and food sources for native wildlife. See Grow Me Instead: Beautiful Non-Invasive Plants for Your Garden. 
• Dispose of invasive plants in the garbage. Do not put them in the compost or discard them in natural areas. Discarded flowers may produce seeds.
• When hiking, prevent the spread of invasive plants by staying on trails and keeping pets on a leash.
• If you’ve seen garlic mustard or other invasive species in the wild, please contact the Invading Species Hotline at 1-800-563-7711 or visit www.invadingspecies.com to report a sighting.