Narrowleaf vetch (Vicia sativa) is a common winter annual weed in the legume family, and it fixes its own nitrogen from the atmosphere. This plant has been grown since Roman times for livestock fodder and as a cover crop.
Narrowleaf vetch is thought to be native to southern Europe or Southeast Asia and has spread throughout most of North America, mostly through agriculture. The plant has purple flowers and produces seed pods that turn from green to black as they ripen and can contain from 5 to 12 seeds per pod. Seeds can remain viable for up to five years. The plant is tolerant of many site conditions and grows in sun to part shade and in dry sandy soils to moist clay loams.
The weed has a tap root that breaks easily, making it difficult to remove when weeding by hand. Mulch is not very effective in preventing vetch from becoming established in landscape beds, and pre-emergent herbicides do not offer very effective control. If this weed has invaded your landscape, use a digging tool to remove as much of the root system as possible. Remove as much of the weed as possible before seed production begins.
There are post-emergent herbicides labeled for control in the lawn and landscape beds. For more information on herbicide recommendations, see: HGIC 2301, Broadleaf Weeds.