Garlic mustard flowers in early spring and then broadcasts its seeds. This is the time to remove it.
Each garlic mustard plant produces thousands of seeds that are believed to be dispersed by the fur of animals such as deer and squirrels and by people. The plant grows heartily in Riverwoods and most vigorously in areas of trampled and disturbed soil. Seeds are produced within days of initial flowering. The seed pods open about a month later.
Garlic mustard is a biennial, growing over a two-year period. In the first year, it is a low rosette. In the second year it is a tall, seed-producing flowering plant. Because seeds can be viable for 12 years, control of an infestation requires activity for several successive years. Garlic mustard can grow in deep shade to full sunlight and in a wide range of moisture levels.
Garlic mustard poses a severe threat to native plants and animals. It crowds out other plants, monopolizing moisture, nutrients and soil space and reducing the food supply for native animals. Native animals do not eat garlic mustard, and butterflies are not attracted to it. In fact, garlic mustard is toxic to some native insects, including butterflies. Garlic mustard is also believed to contaminate the soil with chemicals exuded from its roots. These chemicals inhibit the growth of other plant species.
Hand pulling. Hand pulling of the plants before or within a week or so after flowering is the most common method of control. The entire root must be removed or it will re-grow. A moist soil, such as after a rainfall, makes the hand pulling much easier. To prevent re-seeding, the pulled plants should be removed from the site.
Cutting. Cutting the plant immediately after flowering, and before seeds develop, is effective, but only if the plant is cut at the soil level. Cutting earlier or higher will prompt the plant to re-grow. Cutting later will require removal of plants from the site to prevent re-seeding.
Chemical treatment. Chemical treatment with an herbicide should be done carefully. It risks injuring or killing nearby vegetation.