"What is that plant?" someone asked as we drove along a forest preserve border. "That plant," a dainty light green thing with scalloped leaves and delicate white flowers growing in large stands was garlic mustard, a noted scourge of woodlands across the eastern US, including Illinois. Used as a potherb to flavor soups and stews in Europe, settlers brought it here as a tasty, easy-to-grow bit of home. And it is pretty good, its faint garlicky smell translating into fine taste in cooked dishes.
Garlic mustard (Alliaria petiolata) and I go back a long way. I've spent whole Saturdays in the company of others pulling plant after plant. Just two weeks ago I spent a rainy Sunday morning helping the stewards of Thatcher Woods lead some fifty girl and boy scouts and their attendant adults into the woods; and while introducing them to the delights of such plants as Jack-in-the pulpit, and explaining how that reddish plant really is poison ivy and next time you go to the woods you should wear long pants, we got them to pull whole bags full. To say it is omnipresent is an understatement. May is Invasive Species Awareness Month (see it on Facebook), and I nominate garlic mustard as my personal poster plant.
Why did we put it in bags? Because if it's in flower and you leave it on the ground after you pull it, this biannual will both produce seeds and re-root itself. A single parent plant will produce hundreds of children, and if not harvested prior to seeding, each will produce seeds that are viable for five to seven years. In addition, the roots are allelopathic, that is, they produce chemicals that render the soil great for garlic mustard, not so good for other plants. American insects don't like it, and deer, who feast on trilliums and other beloved flowers, won't touch it.
Now the thing is, it is a pretty plant, and potentially useful--but it's out of control. I thought my garden was safe. I'd seen little of it around town, but maybe because of the rain we got last year, this year there's been a population explosion, and last week I found a healthy stand in my neighbor's back patch by the alley. It volunteers in people's yards and they innocently leave it be. Like I said, it's pretty. Trying to keep my voice low and reasonable, so as not to sound like a maniac, I persuaded them to let me pull what I could and smother the rest with my favorite weedkilling mulch of six layers of wet newspaper covered with several inches of wood chips.
In Gaia's Garden, permaculturalist Toby Hemenway says that such plants shouldn't be called invasive, but rather "opportunistic," since they take the opportunities offered by disturbed environments and nature uses them to fill niches otherwise unoccupied. He says that often, as the ecosystem recovers, such plants will decline to a more reasonable proportion of plant species. Maybe so. However, in my experience, sometimes you have to control the plant to help the ecosystem recover. In Thatcher Woods, once we began to get rid of the garlic mustard and buckthorn, plants that not seen in decades started to grow in the woods, which now is a healthier ecosystem.
How is it controlled? In Thatcher Woods we pull, pull, and pull some more. Some land managers pull it in spring and then in fall use herbicide on the low rosettes that regrow before winter. The Wisconsin Department of Natural Resources has a very informative page, as does the Illinois Natural History Survey. But lately I've been thinking about how we humans are so good at depleting resources and decimating species. Perhaps we should put this talent to good use. Several local examples come to mind. Asian carp approaching Lake Michigan? Start a serious commercial fishing industry--with no catch limits--process the fish and export it to China. Buckthorn? Start a commercial business to make rustic trellises and garden furniture and promote them online and at farmers' markets. Problems solved.
And garlic mustard? Recently I learned that it makes ok pesto. A little online searching found several tempting recipes that look pretty tasty. Some enterprising folks could harvest it and start a business, making and selling pesto at farmers' markets and gourmet food shops. Maybe Whole Foods would be interested. It would be the perfect locally-produced food item, and would compete favorably in cost with that expensive basil stuff from Italy. After all, the basic ingredient is free. You could exploit this resource without feeling the least bit guilty. So hey everyone, let's go.
This Saturday, as I go out to pick again, I plan to bring some home and make pesto. The Mid-Atlantic Exotic Pest Plant Council has some recipes here, at least one of which I intend to try. I'll post the results.
Note: There are, of course, many other invasive, or opportunistic, plants. Go here for a general list of fact sheets. The Chicago Botanic garden offers information here. Unfortunately, many growers and nurseries are not always as responsible as they could be, and sometimes sell known invasive species. To find out about garden invasives and good, native or non-invasive alternates that are easy to find at nurseries and plant centers, here is a list at the Chicago Botanic Garden.