Interior landscaping. In any parking lot containing 20 or more parking spaces (except a parking garage), 5% of the total area of the lot shall be devoted to interior landscaping. Such interior landscaping may be used, for example, at the end of parking space rows to break up rows of parking spaces at least every 10 parking spaces, and to help visually define travel lanes through or next to the parking lot. Landscaped areas situated outside of the parking lot, such as peripheral areas and areas surrounding buildings, shall not constitute interior landscaping. For the purpose of computing the total area of any parking lot, all areas within the perimeter of the parking lot shall be counted, including all parking spaces and access drives, aisles, islands, and curbed areas. Ground cover alone is not sufficient to meet this requirement. Trees, shrubs, or other approved material shall be provided. At least one shade tree shall be provided for each 300 square feet (or fraction) of required interior landscaping area. These trees shall have a clear trunk at least five feet above finished-grade level. Parked vehicles may not overhang interior landscaped areas more than 2 1/2 feet. Where necessary, wheel stops or curbing shall be provided to ensure no greater overhang; and, if a parking lot of under 20 spaces is built without interior landscaping, and later additional spaces are added so that the total is 20 or more, the interior landscaping shall be provided for the entire parking lot.