Upon any lot which abuts a boundary of a residential zone, there shall be established a landscaped strip along the entire length of said boundary. Said landscaped strip shall consist of any one or more of the following: plant material, fencing, walls or grassed areas. Said strip shall be of a width of not less than 50 feet, not including an intervening street, if any, and shall be shown upon the site plan which shall be approved as provided herein.