There shall be permitted fountains, ponds, sculptures, planters, walkways, flagpoles, light standards and decorative screen type walls as elements of landscaping in areas designated for landscaping. Decorative type walls, planters, and sculptures shall be 30 inches or less in height. The city plan commission shall be authorized to permit heights in excess of 30 inches where such is in the best interest of landscaping and will not in the city plan commission’s opinion create a problem relative to public health, safety, order, convenience, prosperity and general welfare.