April is a joyful month, when we plant new trees, transplant or divide late-blooming perennials, cast seeds for early vegetables, and fill our window boxes with frothy, almost shamelessly brilliant flowers known as cool-season annuals.
But as we putter in the garden, or enjoy a spring-break walk, seeking out cherished wildflowers, bulbs, and other early bloomers, we should take every opportunity to spot one of the most invasive plants in our area—garlic mustard, Alliara petiolata. Don't be fooled by the name. Today, it offers no beneficial culinary component in spite of what the early Europeans may have thought when they tucked it into the ship's hold and introduced it to the New World, the land of opportunity, where it had no natural enemies and thrived beyond the colonists' wildest dreams. It does exude an onion-like, garlicky smell when crushed (an excellent aid in identification), but this exotic is not a welcome kitchen herb similar to the ornamental onions (Allium).
What's all the fuss?
Garlic mustard is an invasive plant, capable of choking out native eco-systems as it carpets woodland floors, wetland banks, roadsides, alleys, backyards, and forest preserves. Tolerant of sun, shade, wet, or dry, it out-competes native plants through its aggressiveness, shocking seed production, and ability to release toxins in the soil that prevent native seedlings, including certain species of trees, from thriving.
First year
It is a noxious weed, normally noticed around tax day (easy to remember), perhaps in your own garden, or even slyly growing in the potting soil of a new perennial you just purchased. More likely, it is seen in wild, natural areas. It is biennial, spending its first year as a low-growing rosette of scalloped leaves, all the more pernicious for its ordinariness. The nondescript plant remains green over winter, even under the snow.
Second year
It is the second year, however, when the plant does its most damage, again beginning in April, when its growth really takes off. The leaves assume a more triangular shape, the plant bolts, and its flower stalks push out almost three-quarters of an inch a day. It's in a real hurry to grow, flower, and set seed, for one plant can produce thousands of seeds. It's all over by June. The slim seed pods turn papery, the parent plant dries up and dies—but those mustard-like seeds have now dispersed, either attached to an animal, a gardener's or naturalist's pant leg or boot, or into the soil, where they can remain viable for five to ten years.
What YOU can do
Identify garlic mustard properly—a process most gardeners, school kids, and the public find easiest during its second year, when the plant is actively growing. Watch carefully because it grows so fast. At maturity, it reaches 3 feet or more and is often spotted in great stands, usually in bloom and exceptionally dangerous. The leaves are triangular with toothed edges and are much larger at the base of the plant. It has multiple stalks with developing or fully formed flowers at the tips. Flowers are white with four petals. The plant smells like garlic when crushed.
How to remove the plant
It's important to remove the whole plant, including all of its fleshy root. Even a tiny remnant left in the soil will regenerate. Gently pull the plant out (if the soil is moist this job is easier) by grasping it low on its stem. Do not shake it or compost it! Put it in a plastic bag and tie securely. Contact your village or city for specific instructions on disposal. Many local communities organize group pulls in their forest preserves or other shared land areas. Join in! It's another wonderful way to honor Earth Day.
For more information on invasive plants; what the Garden is doing; and how you can help our conservation efforts, visit www.chicagobotanic.org/invasive.
Other Resources
http://www.inhs.illinois.edu/research/VMG/gmustard.html
http://www.nps.gov/plants/ALIEN/fact/alpe1.htm
Visit the Stewardship Network online.
Lee Randhava is a horticultural writer who lives and gardens in Evanston, Illinois.