A now outdated solution for foliage movement outside unity's terrain, I've taken the vertex movement part from here. Thanks, GambinoInd!
You can also control the behaviour of the movement by tweaking the values from "CustomWind", a script that must be inside of any game object in your scene, works like a cheap wind zone. Needs Blender for .blend models.
Now I do have a solution for bark movement through vertex colors, not here yet, maybe in a new repository.
