Garlic mustard (Alliaria petiolata) is a phenomenally successful plant. In its native range it grows from Ireland to China and from Africa to Scandinavia. In North America, where it is introduced, it is frankly rather too successful. Unpalatable to native grazers and naturally vigorous, it has become a serious invasive pest. As well as taking up space, it produces chemicals which interfere with the native mycorrhizae and sets a nasty ecological trap for a native butterfly. The caterpillars of some species of garden white butterfly naturally feed on toothwort (Dentaria). Unfortunately, garlic mustard looks very like toothwort and the butterflies are suckered into laying their eggs on it. When the larvae hatch, they are unable to digest the garlic mustard and soon die.
In its native range, garlic mustard (a.k.a. hedge garlic, Jack by the hedge and sauce alone) is much better behaved and an excellent candidate for the forest garden. Every part of it is edible, including roots, leaves, flowers and young seed pods. Flavour-wise, it does what it says on the tin, tasting like a cross between garlic and mustard. The roots are the hottest part, with a horseradish-like bite.
Garlic mustard is quite early to come into leaf and the youngest leaves are the mildest, so it’s a useful winter/spring green. As the year goes on the leaves get hotter and a bit acrid. I use them in salads and as a pot herb and often stick a leaf or two into sandwiches. There are much more imaginative ways to use it than this however. The one upside of the garlic mustard invasion of North America is that people have put some serious effort into finding ways to cook them in an effort to eat the interloper into submission.
Pesto seems to be a favourite, with the oily ingredients acting to balance the mustardiness. One recipe combines the pesto with green lentils and one particularly adventurous one throws in the roots for good measure. Garlic mustard roulade wins my prize for the most beautiful recipe and one person has even pickled the roots which must taste amazing.
Garlic mustard is a biennial, growing lots of leaf in its first year then running to seed in its second. It is a very vigorous seeder, so unless you want to end up feeling like North America, I suggest that you pull up most of the plants in the second year and just leave a few to provide the next generation. Be prepared to treat it as a weed in the rest of the garden and hoe it out ruthlessly if it seeds beyond where you want it. It is shade tolerant, growing in either full or partial shade (under a Victoria plum in my case) and not fussy as to soil.