Garlic mustard is a prime example of a good plant gone bad when brought to non-native lands as an invasive species.
Garlic mustard (Alliaria petiolata) has been used for thousands of years in cooking and its native habitat includes Europe, western and central Asia, and northwest Africa.
The leaves are chopped and used in salads as well as in pesto, much in the same way basil is used. When the leaves are crushed they smell like garlic, thus the name — although the two plants are not otherwise closely related.
It has picked up many colloquial name and nicknames over the centuries such as Jack-by-the-Hedge, hedge garlic, garlicwort, sauce-alone, Jack-in-the-Bush, penny hedge, and poor man’s mustard.
In Europe and other natural habitats a host of insects and fungus feed on garlic mustard and keep it in check.
In North America, however, garlic mustard has no natural enemies so it has spread unchecked since it was brought to the U.S. as a medicinal herb in the mid 1800s.
Garlic Mustard in North America
Garlic mustard has been particularly devastating in North America, due to its ability to produce allelochemicals such as allyl isothiocynate and benzyl isothiocynate.
These allelochemicals suppress mycorrhizal fungi that many plants and trees in North America need to grow, giving garlic mustard an edge over many other native species in the race for nutrients and sunlight.
Deer and other foraging animals also avoid garlic mustard. Its seed can also lie dormant for years before germinating, making eradication and exhausting the seedbank very difficult once it is established.
Deer are also thought to help spread the plant by both eating competing natural species as well disturbing the soil and helping spread seeds.
Many states with large deer populations have been particularly impacted by the spread of garlic mustard.
Identifying Alliaria petiolata
Garlic mustard is a single-stemmed biennial or winter annual herb that typically grows to about 3 feet tall, but can grow as tall as six feet under optimal growing conditions.
One of its most distinctive features are small white flowers that appear in early spring in clusters at the top of the plant; garlic mustard will be the only plant with white flowers in early spring.
First year plants are low-growing rosettes with rounded, scalloped leaves. The leaves are smooth and not fuzzy or hairy as is the case with other species that resemble garlic mustard.
Upper leaves on mature plants are triangular, jagged and toothed, and decrease in size toward the top of the plant. When crushed the leaves will produce a noticeable garlic odor.