Garlic mustard. (Courtesy photo )
An aggressive newcomer has taken root along many of Harvard’s scenic roadsides—garlic mustard (Alliaria petiola). A prolific seeder, garlic mustard quickly forms large stands that crowd out native species. You can spot its delicate white flower and bright green, rounded leaves with saw-toothed edges along roads, trails, and parking areas. This invasive plant thrives most readily where the soil has been disturbed.
As a biennial, garlic mustard has a two-year life cycle. The first year it forms a rosette of leaves. In its second year, it flowers and sets seed—up to 17,000 seeds per square yard! Seeds can last up to five years in the soil, so it is important to eradicate plants as fully as possible before seeds become established in an area.
There are several effective methods of eradication: (1) Pull the plants by hand, being sure to get the root crown as well. Bag and remove the plants you uproot; don’t leave them on the ground, as the seed can still ripen. (2) Use a string trimmer to cut the plants close to the ground. While this method is faster than hand pulling, it does not remove the roots. For that reason, you will have to repeat the process several times during the season. Again, remove the clippings. (3) Spot treat the garlic mustard with a herbicide. The best time to use this method is in the early spring or late fall, when few other plants are up. Garlic mustard continues to grow as long as the temperature remains above freezing and the ground is clear of snow.
Left uncontrolled, garlic mustard has been known to spread up to 120 feet per year. In other words, give it an inch and it will take your yard!
Marty Green
President, Garden Club of Harvard
