If an ordinary window is to become a “Still Life with Plants,” it must first be outfitted for a multi-level display of pots. The sill is the most logical place to start.
Most windowsills are pathetically narrow. The simplest answer to a narrow sill is a foot-wide board or wooden shelf, fastened on a level with the sill as an extension. Paint or stain the board to match your window’s existing trim.
Or you can use an attractive piece of furniture that matches the height of the existing sill—for the window pictured here, a bookcase makes a broad surface for plants.