Crown vetch is an herbaceous perennial that spreads aggressively by the growth of rhizomes and also reproduces readily from seed. It can form dense, nearly monotypic stands on sunny sites and crowds out most of the other vegetation. It has been widely planted to stabilize soil, especially after road construction, and it persist for many years afterward and spreads into adjacent natural habitats.

An additional problem arises from its use on sandy soils of low productivity. Such soils provide habitat, refuge of a sort, for native plants that can't compete with the robust agricultural plants that thrive on productive soils. Crown vetch is a legume and in league with bacteria it can "fix" nitrogen from the atmosphere into a chemical form that plants can use. That nitrogen is ultimately added to the soil and effectively fertilizes the site, thereby encouraging the growth of weeds, and the habitat is lost to native species even if the crown-vetch is later removed.