Just putting the stencils in that folder won't get them to be seen by Visio. You need to put them in the My Shapes folder under your My Documents. The correct way to install new stencils is via an installer (.msi) file. This file will contain publish information that tells Visio which category the stencil will be under as well as the display name of the stencil i.e. the bit that transforms the name PLANT_M.VSS to Planting.