Such a cool idea! You just need a blender, a blank wall, and a few special ingredients to paint your moss graffiti design.
Gallery of Living Walls - Habitat Horticulture
Garden Wall - metal planters on brick Reuseable plants and wall hanging - great for offering vertical interest - tropical vines?
Vertical in Loft JM Dimanche, Paris, by Patrick Blanc
Vertical garden of ferns! How about a variation of this leaning against the south side of the front yard or the north fence in the back yard? garden,Gardening,Gardens,In the Garden,
Florafelt Vertical Garden Guide make creating living walls easy! They are even suited to growing herbs and vegetables organically :)