A buffer zone shall be provided between the business districts and any residential districts, the same to consist of a strip of land not less than 10 feet wide along the entire boundary line. Such area shall have plantings of hardy-type evergreens, with a minimum height above ground when planted of five feet, spaced not more than four feet apart, and shall be provided near and along the entire boundary. The buffer zone shall be kept free and clear at all times of all merchandise, merchandising display material, signs, boxes, cans, rubbish, trash, debris, etc.