In Canada, it occurs mainly within the Mixedwood Plains Ecozone, indicated by the hatched area. I n Ontario, the province of its most abundant occurrence in Canada, its northward spread appears to be limited by the presence of the Precambrian Shield, a region of soils derived primarily from ancient acidic bedrock. From at least these two centres, garlic mustard spread rapidly throughout southcentral and southwestern Ontario during the last 50 years. Its spread throughout southeastern Ontario and adjacent southwestern Quebec dates from the 1890s. It is now abundant in many natural sites throughout this region.
Garlic mustard is also locally common in the Quebec City region.
Its widespread occurrence in southern Ontario likely reflects the high proportion of disturbed woodlands and urban sites available, the high human population levels in the region and the ample presence of soils and habitats rich in lime. Biology G arlic mustard is a biennial that developes a rosette of leaves from a slender tap root during the first year of its growth. This tap root characteristically grows almost horizontally for part of its length. May. Various insects, including flies and bees, have been reported as possible pollinators. Normal seed production occurs, however, when the plants are self-pollinated.