Non-Native Invasive Species

Garlic mustard

Alliaria petiolata

Garlic Mustard

Garlic Mustard
Illustration by Anne Hunter

Native biodiversity, the plants and animals and other organisms typical of a region and expressive of its climate, soils, topography and other physical features, is increasingly endangered. Development of all kinds is the major threat, followed closely by organisms from elsewhere. Everyone is familiar with imported diseases such as Dutch elm disease or imported insects like gypsy moth. But plants from elsewhere can and do pose threats too. Some of the worst non-native, invasive plants are readily apparent along roadsides and in yards or woods or fields right now. Among them is garlic mustard, a plant originally from Europe.

The species is easy to recognize this time of year. Deep green crinkled leaves, kidney-shaped near the base of the plant and triangular nearer the top, now clothe a spike up to two feet tall bearing several clusters of white flowers. (Up close, the leaves, when crushed, smell of garlic.) The plant seldom grows alone but instead forms colonies which may cover large areas along roadsides or in woods.

Garlic Mustard

Common Buckthorn
Photo: Olivia Kwong, Plant Conservation Alliance, Washington, DC

The species is a biennial (it dies after flowering in its second year), so plants in bloom now are not long-lived. They will, however, have many replacements, for each mature plant produces hundreds of seeds, which germinate quickly. Young plants will overwinter as a round, short clump of leaves called a rosette.

Why is garlic mustard a problem? Along roadsides, it really isn't: few native plants grow naturally in such disturbed sites anyway. But in the woods, especially on the edges or where the woods have been disturbed by logging, garlic mustard seems to replace native wildflowers and even some shrub and tree species. Garlic mustard is also a threat to several butterflies. Adult butterflies, confused by the chemical similarity of garlic mustard to native wildflowers such as toothwort, lay eggs on garlic mustard. Young caterpillars, which have evolved to feed on toothwort and native plant cousins, are less likely to survive on garlic mustard.

Garlic Mustard

Common Buckthorn
Photo: Olivia Kwong, Plant Conservation Alliance, Washington, DC

The best way to control small patches of garlic mustard is to cut the flowering spikes before seed is set. And keep at it, year after year, until all the seed in the soil has germinated. (This could take five years or more.) Winter rosettes can be fairly easily pulled. And eaten, in late spring. The plant was probably brought to North America for culinary reasons (just as cabbage and broccoli and other mustard family relatives were). Some studies have found the species to be unusually high in Vitamins C and A.