In the first year, plants reach a height of only a few inches, and may be hidden under dead leaves in spring. First year leaves are kidney-shaped and form a basal rosette. The basal leaves are retained in the second year, and differ in shape from the triangular second-year leaves, which are alternate on the stem and become smaller towards the top of the plant. The small white flowers have four petals and are clustered at the top of the stem. The seeds are contained in green pods and are dispersed when the capsules burst open in the fall.
Plants retain their green color throughout the winter.
Unlike many weeds, garlic mustard is shade-tolerant. It can quickly come to dominate the forest floor, growing in dense stands and displacing native woodland wildflowers. In less than a dozen years, garlic mustard is capable of virtually eliminating some spring wildflower populations. Garlic mustard seeds appear to spread rather easily via animals, humans, and flowing water. The species often invades along trails or streams.