Garlic Mustard is an introduced and naturalized biennial. First year plants form a basal rosette which flowers the second year when it raises an unbranched hairless stem that can be 4 inches to 4 feet high.
Leaves: The basal leaves are ovate to oval with a heart-shaped base, with very coarse teeth and a long stalk. Second year stem leaves are more triangular shaped with rounded lobes on the margins, tapering to a rounded point at the tip and a more truncate base tapering to a short stalk. The underside is paler in color and has hair on the underside. The leaves produce a garlic smell when crushed.
The inflorescence is a short terminal raceme of stalked flowers. Clusters may also rise from the upper leaf axils. These racemes are short at first but like many mustard family plants, once flowers bloom, the raceme elongates as seed pods form below.
Flowers are 4-parted, with a short calyx that has four whitish sepals with green tips and 4 white petals that have rounded lobes and claw-like bases. Petals are longer than the sepals. Stamens number six, with two shorter than the others, white filaments and yellowish anthers and there is a single short green style with a blunt tip.
Seed: Garlic Mustard flowers very early in spring and continuously into summer and produces huge quantities of seeds which can lie dormant for years. The seed pods are long and thin, with 4 angles, and horizontal or upward pointing and contain a flat row of dark brown to black ribbed seeds that are attached to two sides of a central membrane in the pod. The seeds are oblong, tapering to a sharp point. They will remain viable in the soil for 5+ years.
Habitat: Garlic Mustard produces a fleshy tough branching taproot, but mainly spreads by re-seeding. It colonizes from an established area outward and if unchecked will cover vast areas, preventing growth of other plants. It easily moves into disturbed areas and woodland edges. It adapts to many soil types and moisture conditions except constantly moist soils. It prefers full sun, but does well in partial shade. It has no known pests and deer and other browsers avoid it.
Names: The genus Alliaria comes from 'Allium' for garlic or onion, and the Latin aria, meaning 'a connection' which all refers to the plant having a garlic odor when crushed. The species petiolata means 'with a leaf stalk', which differentiates this species from other Alliums. The authorship of the plant classification is as follows: First to describe was ‘M.Bieb.’ who was Friedrich August Marschall von Bieberstein (1768-1826) German botanist and explorer who published several works on the flora of parts of Russia. His work was updated by two others. ‘Cavara’ is Fridiano Cavara (1857-1929) Italian botanist who was director of the botanical garden in Catania Sicily and then director of the Naples Botanical Garden and ‘Grande’ who is Loreto Grande (1878-1965), Italian botanist who worked at the Naples Botanical Garden. In earlier times the plant was classified as Alliaria officinalis.
Above: Plants can flower as early as late April and surpass in height anything else at that early date. 1st photo - The second year stem leaves are more triangular shaped with rounded lobes on the margins, tapering to a rounded point at the tip and a more truncate base tapering to a short stalk - different from other Alliums. 2nd photo - Characteristic Mustard family seed pods already forming while some flowers are still in bloom. 3rd photo - The fleshy tough branching taproot. In dry soils it will snap off allowing the plant to re-sprout.
Below: 1st photo - Of the six stamens, two are shorter than the other four. The four petals have rounded lobes and clawed bases. 2nd photo - The calyx has four whitish lobes with greenish tips.
Below: 1st photo - Notice the height of the plants in early May in an area where volunteers are about to begin removal (photo courtesy of Melissa Hansen). 2nd photo - Typical Garlic Mustard plants, each stem an individual plant, they branch only near the top.
Below: The basal leaves are ovate to oval with a heart-shaped base, with very coarse teeth and a long stalk. The underside is paler in color and has hair on veins. The basal leaves (far below) are more ovate with a heart-shaped base.
Below: The seed pods are long and thin, with 4 angles, and contain a flat row of dark brown to black ribbed seeds that are attached to two sides of a central membrane in the pod. The seeds are oblong, tapering to a sharp point.
Below: A large first year rosette formed last year that result in several large flowering stems in a few weeks.
Notes on removal and Eloise Butler Wildflower Garden: Sometimes found in both the Woodland and Upland Gardens and in many areas of Wirth Park outside the Garden boundary. Garlic Mustard is an officially designated invasive species. It is subject to continuous removal work in the Garden and the Garden surrounds. Removal work from the Garden by Garden staff and by volunteers has been very successful over the last 10 years. Plants appearing now within the Garden boundary are usually from long-dormant seeds in the soil or from seeds blown in from adjacent park areas where the plant has been present in large numbers.
Safe removal methods are by pulling the entire plant including the tap root or by cutting at ground level. Plants must be bagged as pulled plants left on the ground will produce seed. Cutting just the top usually results in a new flower cluster forming. On large infestations, glyphosate can be applied in early spring or late fall when native plants are dormant. If left untended, Garlic Mustard will within 10 years suppress most native herbaceous plants. It should be eradicated wherever found. It is listed on the "Prohibited noxious weeds" list in Minnesota.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"