Garlic mustard (Alliaria petiolata)

Synonyms: Alliaria officinalis, Alliaria alliaria, Erysimum alliaria, Sisymbrium alliaria

Common Names: Hedge garlic, jack-by-the-hedge, poor man's mustard, garlic root, garlicwort

Description:

Garlic mustard (Alliaria petiolata) is an invasive plant from Europe and western Asia that was first recorded in North America in 1868 and has since spread through woodlands across much of the eastern and midwestern United States and parts of Canada [1][5]. It takes over the shaded floor of forests, crowding out native wildflowers and tree seedlings [3]. MISIN tracks it because its roots release chemicals that harm the soil fungi that native trees and wildflowers depend on [3].

Habit:

Garlic mustard lives for two years and looks very different in each one. In its first year, it grows as a low cluster of rounded, kidney-shaped leaves with scalloped edges that stay green right through winter [2]. In its second year, it sends up a stem 1 to 3 feet tall topped with small white flowers [2]. The surest test is the smell: crush a leaf or stem between your fingers and it gives off a strong garlic odor, which no native look-alike shares [2][5].

The best time to spot it is early spring. The first-year clusters are easy to see on bare forest floors before native wildflowers come up, and second-year plants flower from late April into June, standing out as patches of white in the shade [2]. By midsummer the plants set slender seed pods and then die back [2].

At-a-glance cues:

1. Crushed leaves and stems smell strongly of garlic [2][5]
2. First-year plants are a low cluster of rounded, scalloped leaves that stay green all winter [2]
3. Second-year plants grow 1?3 feet tall with small white four-petaled flowers at the top [2]
4. Slender, upright seed pods line the upper stem after the flowers drop [2]

Leaves:

1. First-year leaves: rounded to kidney-shaped with scalloped edges, in a low cluster (basal rosette) close to the ground, up to about the size of your palm [2]
2. Second-year leaves: alternate (one per spot on the stem), more triangular to heart-shaped, with coarsely toothed edges [2]
3. Leaf surface is smooth and mostly hairless, on a distinct leaf stalk ? a quick way to separate it from fuzzy-leaved look-alikes [2]
4. Leaves of all ages smell of garlic when crushed [2][5]

Stems:

1. Soft and green (herbaceous), not woody [2]
2. Erect, usually 1?3 feet tall, occasionally taller [2]
3. One or a few stems rise from the first-year cluster in the second spring [2]
4. The white taproot often has a small S-shaped bend just below the stem [2]

Flowers:

1. Small and white, each with 4 petals arranged in a cross [2]
2. Held in tight clusters at the tops of the stems [2]
3. Bloom from late April through early June [2]
4. Each flower has both male and female parts, so plants set seed readily [2]

Fruit and seeds:

1. Fruit is a slender, upright seed pod up to about 2.5 inches long [2]
2. Pods ripen from green to tan in summer, then split open to release seeds [2]
3. Each pod holds roughly a dozen or more small, dark seeds [4]
4. A single plant can make hundreds to several thousand seeds [4]

Habitat:

Garlic mustard grows best in shade and partial shade. It is most at home on the floor of hardwood forests, but it also fills in along forest edges, trails, roadsides, riverbanks, fence rows, and shady spots in yards [2][5]. It does well in moist, rich soils and spreads fastest where the ground has been disturbed [2].

The plant is native to Europe and western Asia [1]. In North America it now ranges across much of the eastern and midwestern United States and into Canada [1]. It is one of the few invasive plants that can take over a shaded, undisturbed forest understory, not just disturbed ground [3].

Reproduction:

Garlic mustard spreads only by seed, and the seeds travel easily on things people and animals move around. They hitch a ride in the mud on your shoes, on clothing, on mowers and other tools, on vehicle tires, and they wash downstream in water [4][5]. That is why new patches so often show up along trails, driveways, and creek banks. A patch in a neighbor's yard or a nearby park can seed your property within a season or two.

The plant lives for two years. A seed sprouts in early spring and spends its first year as a low cluster of leaves. The next spring it shoots up, flowers, sets seed, and dies. A single plant can produce hundreds to several thousand seeds [4]. Those seeds can survive in the soil for many years ? commonly cited as up to about 10 years ? so a patch keeps coming back long after the visible plants are gone [4]. The key to control is timing: pull or cut second-year plants before the flowers turn into seed pods, usually before June, to stop new seed from forming [4][5].

Impact and Damage:

Garlic mustard is not known to harm people or pets ? it is not poisonous and is even edible ? so the damage shows up in your garden and the woods, not your health. In shady gardens and woodlots it spreads into a dense carpet that pushes out native wildflowers, ferns, and tree seedlings and leaves little room for anything else [3].

The deeper problem is below ground. Garlic mustard's roots release chemicals into the soil that kill the helpful fungi (mycorrhizae) that most native trees and wildflowers rely on to take up water and nutrients [3]. In a controlled study, soil affected by garlic mustard had almost no detectable beneficial fungi, and native tree seedlings grown in it grew poorly ? the harm came from the damaged soil fungi, not from competition for light or water [3]. Because the plant itself does not need these fungi, it gets ahead while its neighbors fall behind [3]. Over time this can reshape a forest understory and slow the regrowth of native trees [3].

Similar species:

Several plants can be mistaken for garlic mustard, especially the first-year clusters of leaves. None of them smell of garlic when crushed, which is the quickest way to tell them apart [2].

Creeping Charlie (ground ivy) is a low, non-native plant with rounded, scalloped leaves much like a first-year garlic mustard cluster, but its stems are square and trailing and it has no garlic smell [2]. Common violets form low clusters of heart- or kidney-shaped leaves too, but their roots grow straight down rather than from an S-shaped taproot, and they lack the garlic odor [2]. Native toothworts are spring woodland plants in the same mustard family with white four-petaled flowers, but their leaves are deeply cut into narrow segments and have no strong garlic scent [2]. Sweet cicely can look similar in leaf, but a crushed leaf or root smells of anise or licorice, not garlic [2].

Monitoring and rapid response:

Signs to watch for:

1. Low clusters of rounded, scalloped, evergreen leaves on the forest floor in early spring [2]
2. Patches of 1?3 foot plants with small white four-petaled flowers from late April through June [2]
3. A garlic smell when you crush a leaf or stem [2][5]

What you can do:

1. Pull plants in the spring of their second year, before the flowers open (usually before June), so no seed can form [4][5].
2. Grab the plant at its base and pull up the top of the root too ? it can resprout if the root crown is left behind [5].
3. Bag what you pull, including any flowering or seeding plants, and put it in the trash ? not the compost, since seeds can still ripen on pulled plants [5].
4. For a few first-year clusters, hand-pull them; cutting plants off at ground level right as they flower also works [5].
5. Plan to repeat every year for several years ? seeds survive a long time in the soil [4].
6. Natural area crews should start in the healthiest, least-invaded areas and clear small outlying patches first, then work toward the core over repeated visits across several seasons [5].

When to call a professional:

1. Large, well-established infestations across a woodlot or property.
2. Sites where yearly hand-pulling is not keeping the plant in check.
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. USDA NRCS Plants Database. Alliaria petiolata (M. Bieb.) Cavara & Grande. plants.usda.gov
2. University of Minnesota Extension. Garlic mustard. extension.umn.edu
3. Stinson KA, Campbell SA, Powell JR, Wolfe BE, Callaway RM, Thelen GC, Hallett SG, Prati D, Klironomos JN (2006). "Invasive Plant Suppresses the Growth of Native Tree Seedlings by Disrupting Belowground Mutualisms." PLoS Biology 4(5):e140. doi.org/10.1371/journal.pbio.0040140
4. Rutgers New Jersey Agricultural Experiment Station. FS1212: Identification, Control, and Impact of Garlic Mustard, Alliaria petiolata. njaes.rutgers.edu/fs1212
5. Michigan Department of Natural Resources. Invasive Species: Garlic Mustard. michigan.gov/invasives

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