Ideas for shaded bank?

I've got this bank above a ditch that gets little sun, even though it's south-facing.  This is because there are too many trees in the way.  I was wondering if there is anything I could plant here that would help hold soil and enrich it at the same time.  If it provided some kind of food that would be a bonus.  At the very least I would like to put in some kind of perennial.  The ditch below sees a fair amount of moisture but never seems to have actual running water in it.  All forest behind.  This is in Nova Scotia, Canada, on the south shore, Zone 5a.  Thanks in advance. 

I like wintergreen for this task, it would go nicely there IMO