Planter boxes made of wood, precast concrete, stone, brick, or other masonry, which shall be 36 to 42 inches in height. Such planter boxes shall be at least 12 inches wide and have drain holes in the bottom. Planter boxes shall contain dwarf evergreen shrubs, or a combination of flowers and vines, which shall be installed prior to opening the outdoor dining area, and shall be continuously maintained. Any plantings that die shall be replaced immediately thereafter.