I remember the first time I saw garlic mustard. It was the mid-1990s, during a fifth grade field trip to a prairie park in central Illinois. My parents had told me about this botanical invader, new to many areas of the state, spreading through the countryside and outcompeting native species. I hadn’t seen garlic mustard before, but I knew it had white flowers and a sharp distinctive odor.
“If this smells like garlic, I’m going to tear it out,” I told my friends as I crushed its leaves and sniffed. I’d guessed right—and yanked it out by the roots. Such a seemingly destructive act surprised and amused my Catholic school classmates but it was, as I tried to explain to them, ecologically sound.
Invasive plants are a major problem for the United States, and few are more top of mind than garlic mustard in the forests and open spaces of the Midwest and East Coast—where the plant is now flowering. This plant is a menace to forests: Its roots produce noxious chemicals that kill symbiotic fungi that native species rely on, says Don Cipollini, a professor of plant physiology and chemical ecology at Wright State University in Dayton, Ohio. Most animals don’t eat it, so it spreads unchecked.
Garlic mustard plants can each produce several hundred seeds and they are very difficult, if not impossible, to eradicate once established over a large area. Now, while it’s in peak bloom and easy to identify, is a great time to pull it out, Cipollini adds.
But this weedy troublemaker has a limit. Accumulating research suggests it becomes less abundant and destructive over time, and in some cases, it may be best to let it be. And as I learned on a recent walk, garlic mustard is edible—and in small doses, quite tasty and nutritious.
Beware the cyanide, though.
Plant explosion
Garlic mustard has a two-year life cycle. The first year, it lays low to the ground, forming small, rosette-like leaves. In the second year, it shoots upward in early spring, growing to a height of several feet and producing bright white flowers.
Populations of garlic mustard “can really explode,” says Jeffrey Corbin, a plant ecologist at Union College in Schenectady, N.Y. The species has been spreading haltingly throughout the country since the late 1800s, when it was deliberately introduced to Long Island from its native Europe.
The plant produces an abundance of glucosinolates, a family of sulfur-containing chemicals present in many types of mustards, which generally have a pungent smell and sharp taste. They give horseradish its kick and make yellow mustard spicy. But in the case of garlic mustard plants, the glucosinolates are also excreted by the roots, killing some of the symbiotic mycorrhizal fungi that most native plant and tree species partner with to draw nutrients from the soil. Garlic mustard, like other members of its family, do not need these fungi to thrive.
The decreased abundance and diversity of these fungi can last for many years after the plant is removed, says Mark Anthony, a fungal ecologist and postdoctoral researcher at ETH Zurich.
There’s also some research showing that this fungi-killing power perhaps weakens native plants and makes germination more difficult, although the scientific record is mixed as to how serious the effect is.
Though all researchers agree it’s important to prevent garlic mustard from spreading to new areas, some researchers think the plant is often not worth spending resources to eradicate once it’s established.
Worth the effort?
Bernd Blossey, a plant ecologist at Cornell University, is one. Research by Blossey and colleagues shows that at more than a dozen plots throughout the Northeast and Midwest, garlic mustard has declined significantly in abundance over the course of recent years. In those places, there’s a “negative soil feedback” happening, where microbes are accumulating that hurt the mustard, he says.
The microbes are likely feeding on the chemicals the roots excrete, including glucosinolates, he says. If you leave the plant alone, and let these microbes accumulate, it will eventually thin out, though it’s unlikely to disappear completely, he adds. By pulling it, you might actually be doing harm, by creating more disturbance, potentially spreading its seeds, trampling native species, and interfering with the soil’s ability to repel the invader, he says: “It all backfires.”
Some researchers think garlic mustard is more harmful than Blossey suggests and that this self-thinning phenomenon is not universal. But there does seem to be a consensus that garlic mustard is not quite as fearsome as thought in the 1990s, for example, when it was new to many areas of the Midwest. (And to me.)
One study led by Corbin at a site in northeastern New York found that to eradicate garlic mustard once it’s established is nearly impossible over a large area. To get rid of it, you’d need to pull up nearly 100 percent of the plants every year over the course of a decade, because up to one-fifth of the seeds can delay germination for years. If you only get 90 percent of the plants, the job could take 50 years, the researchers calculated.
Researchers agree the best option is to prevent it from being established in the first place—or to catch the invasion early, Cipollini says.
But it may not be necessary to eradicate it to save forests. “In many ways its presence is more of a symptom of a disease rather than the cause,” says Richard Lankau, a researcher at University of Wisconsin. “Things like disturbance, overabundance of white-tailed deer, exotic earthworms—those things often seem to set the stage for bad garlic mustard invasions.”
Blossey agrees that unchecked populations of deer are the biggest threat to native plants, and these herbivores also help garlic mustard by avoiding it while mowing down its native competitors. Earthworms, which aren’t native to much of the Northeast, also help decomposing bacteria flourish in the soil and reduce leaf litter, which seems to somehow help garlic mustard.
Aside from plants, garlic mustard does hurt some native insects, such as the beautiful West Virginia white butterfly. Research by Cipollini shows that these insects, which once fluttered widely throughout eastern forests but are now scarce, prefer to lay their eggs on garlic mustard instead of native species of mustard. But when they do, all their eggs die. The same happens with another native butterfly, the falcate orangetip.
Nutritious invader
But as I found out, the plant is edible for humans. While on a walk through a forested park in Washington D.C. last April, at the beginning of the first COVID lockdown, I saw a couple of people off the trail in the brush, bending over collecting something. When I asked, they cheerfully told me they were gathering garlic mustard. The plant can be sautéed and eaten, one of them said. And if you grind it up and cook it, “it makes a great pesto.”
Intrigued, I took to the internet, which told me that the mustard indeed can be added to salads and soups. But Cipollini explains that garlic mustard does produce significant amounts of hydrogen cyanide—the well-known toxic gas—when its leaves are cut or bitten into. This evolved as a type of predator defense, and happens when an enzyme in the plant acts on those same glucosinolates that give the plant its garlicky kick.
But the cyanide is easily sidestepped by chopping up the plant, which releases most of the gas in a few minutes. Soaking and cooking it also reduces the cyanide to negligible levels, Cipollini explains. Some people eat it raw, which in small doses and only done occasionally is also not harmful—and likely healthy, he adds, since it’s high in vitamin C, zinc, and vitamin E. The plant contains less cyanide than many other staple foods, including cassava, lima beans, and sorghum, which are all processed to remove the chemical.
Austin Arrington, the founder of an environmental consulting firm called Plant Group, has studied the feasibility of foraging as a way to potentially help control invasive species (though he cautions that doing so in urban areas always comes with some risks, such as contamination from herbicides or chemicals in the soil). He recommends sauteeing garlic mustard “with butter or olive oil like you would spinach or other greens. I think it would pair well with chicken or pork.”
After my encounter in the woods, I have tried the plant and enjoy its garlicky, oniony taste, which adds a zing to stir-fries and the like, though it’s best used in small quantities and well-cooked, which reduces its bitterness. So while I do plan to keep collecting and eating it on occasion, next time I pass it in the forest, I’ll probably let it be, knowing what my childhood self didn’t: Pulling out a plant here or there doesn’t do much to fight these invasive plants.
