I planted crown vetch to stabilize a ditch bank, but it did not work. The canopy actually shades the soil and it washes pretty easily. Grasses are much better for erosion control.
Yes but crown vetch has never been recommended for stabilizing soils in structures that are intended for carrying water in high volumes. Where crown vetch has exhibited superior performance are on slopes where grass seeds are easily washed away before germinating. The crown vetch seeds are dense and small and some tend to remain on slopes even after rainfall when the planting method is broadcasting. It was a cheap shortcut for DOTs.
Slopes may not absorb sufficient rain water to support the establishment of many grasses from seed. Nowadays new technologies are used to improve grass stand establishment on slopes ... like the netting with seeds interwoven. This provides a mulching effect and keeps seed on the slope. Something like that would have been preferable for your ditch. Where the soil is marginal, its would be beneficial to over seed with a complex of native legumes. Something like this is a good option for any trying to establish coverage on disturbed or barren slopes.
