Whenever I give a talk on invasive species, at some point in my presentation I borrow a page from modern childrearing theory and say; "Species are neither good nor bad. It's their behaviors that we judge as inappropriate." Most of the time, I even mean this. Right or wrong, though, it's hard for me to consider this plant anything but terrible. I hate garlic mustard.
Alliaria petiolata is a phenomenally successful invader in the eastern United States. The Invasive Plant Atlas of New England notes:
"(Garlic mustard) is native to Europe, where it can be found from England to the Czech and Slovak Republics, Sweden, Germany and south to Italy. It has also been reported from Canada. In the United States it can be found from Maine to South Carolina, West to Minnesota, Iowa, Arkansas, Oklahoma, Utah, Washington and Oregon. It has been reported from all New England States."
It's been in this country since 1868 and when I look out at our moist woodlands today, where the spring ephemerals are just starting to rise up through the leaves, more often than not all I can see is a solid blanket of garlic mustard rosettes. Just 1-2% infestation of garlic mustard causes other species to drop out of a natural habitat. The seeds (30,000 per plant), are very light and can be moved by agricultural equipment, road graders, bark mulch, and on the legs of deer. The seeds remain viable for at least five years, so unless you get to the plants during their first year, you are in for a long pull. They also keep invading my flowerbeds from my neighbor's infested yards. They are aleopathic, exuding toxins in the soil to out compete other species (as Sissy Willis noted in this excellent post during garlic mustard season last year.)
It's a miserable plant, even though the white flowers on those long stalks can look pretty, I guess, to the untutored eye, and the greens are theoretically edible. Do yourself a great favor and do not let this get established anywhere you care about. It cannot be reformed.
Some of my enlightened horticultural industry emphasize "the right plant in the right place." The place for Garlic Mustard, outside of its native range at least, is inside a heavy duty garbage bag. It will just resprout on your compost pile.