Where an existing residential use is located adjacent to a proposed manufacturing or commercial development, the developer shall plant along that part of the side or rear lot line adjacent to a residential use, a row of evergreen shrubs at least four feet high at the time of planting and which are of a type which may be expected to form a year-round dense screen at least six feet high within three years, or trees selected from Appendix B and spaced at 10 feet on center. Such screening shall be maintained in good condition at all times.