Garlic mustard (Alliaria petiolata) is an herbaceous, biennial forb that was introduced from Europe in the mid-1800s. This highly invasive exotic species grows and spreads extremely quickly, forming thick stands that shade-out and out-compete native understory plants and tree seedlings, to the point of completely suppressing their growth. Additionally, garlic mustard can release allelochemicals into the soil that prevent seeds of other species from germinating. Few animals or insects eat this plant in the U.S., so without human intervention it can spread. One garlic mustard plant can produce hundreds of seeds that remain viable in the soil for 5 or more years. These seeds are easily spread on the fur and feet of animals and through human activity.
Garlic mustard has two different growing phases. In the first year, seedlings have round or heart shaped leaves with scalloped edges that often resemble creeping charlie. In the second year, the plant produces a stalk with triangular leaves that are sharply toothed. Flowers grow at the top of the stalks or in the leaf axils and long, thin, green pods with shiny black seeds form soon after.
Habitat: Forests, along trails, yards, roadsides; prefers shaded areas but can also be found in full sun
Height: First year: 1-6 inches, second year with stalk 1-4 feet
Site Requirements: Cannot tolerate acidic soil
Leaves: Smell like garlic when crushed. First year: round or heart-shaped rosette 1-6 inches across with scalloped edges, not clasped around the flower stalk; second year: sharply toothed triangular leaves 2-3 inches across, alternately attached to flowering stalk
Flowers: small white with four petals that are 0.25 inches wide
Flowering Dates: April-June
Seed Dispersal Dates: July-August
Seed Bearing Age: Produce seeds in the second year of growth (plants die after seed production)
Garlic mustard plants usually have one or two stems but plants that have been cut will sometimes have more. Plants also have a white taproot.
The Iowa DNR has a guide to controlling garlic mustard throughout the year. Prescribed fire can be used in early spring and can be followed up with torching if seedlings continue to emerge. Hand pulling can be extremely effective from April through June, before seeds start falling. It is important to stay out of garlic mustard infested areas from July through October to prevent spreading seeds. Check out our Chemical Control of Unwanted Vegetation article for herbicides and application methods.