Except where a greater width of planting area is otherwise required by this chapter, the perimeter of each off-street parking area for every building or attached group of buildings having five or more parking spaces shall, wherever such parking area abuts on a public street, except for means of egress and ingress, be effectively screened by not less than a five-foot-wide planting area; whenever such parking area abuts on an arterial highway, parkway, residentially zoned property or on a street abutting residentially zoned property, such parking area shall be effectively screened by not less than a fifteen-foot planting area. Such planting area shall be densely planted with shrubs and trees, pursuant to a plan approved by the Planning Board, and maintained in a healthy and luxuriant condition throughout the year. Every parking area containing at least 12,000 square feet shall have not less than 2% of its interior area devoted to planting areas containing shrubs or trees, which planting areas shall be located and planted pursuant to a plan approved by the Planning Board.