Planting and trees
The provisions of this Section are intended to facilitate a combination of landscaping elements in order to provide comfort, shade and textural variety.
At least 20 percent of the area of a public plaza shall be comprised of planting beds with a minimum dimension of two feet, exclusive of any bounding walls.
All public plazas shall provide a minimum of four trees. For a public plaza greater than 6,000 square feet in area, an additional four caliper inches in additional trees or multi-stemmed equivalents must be provided for each additional 1,000 square feet of public plaza area, rounded to the nearest 1,000 square feet.
For all public plazas, at least 50 percent of required trees shall be planted flush-to-grade or planted at grade within planting beds with no raised curbs or railings. Trees planted flush-to-grade shall be surrounded by a porous surface (such as grating or open-joint paving) that allows water to penetrate into the soil for a minimum radius of 2 feet, 6 inches. Such porous surface shall be of sufficient strength and density to accommodate pedestrian circulation, including all requirements related to accessibility for the disabled, and shall be of a design that allows for tree growth. Installed fixtures such as lighting stanchions, electrical outlets or conduits shall not be located within the required porous area of any tree planted flush-to-grade.
Where trees are planted within a public plaza, they shall measure at least four inches in caliper at the time of planting, unless alternative, multi-stemmed equivalents are specified in the approved planting plans. Each tree shall be planted in at least 200 cubic feet of soil with a depth of soil of at least 3 feet, 6 inches.
Planting beds shall have a soil depth of at least 18 inches for grass or other ground cover, three feet for shrubs and 3 feet, 6 inches for trees. No planters or planting beds shall have bounding walls that exceed 18 inches in height above an adjacent walking surface or the highest adjacent surface where the bounding wall adjoins two or more walking surfaces with different elevations. Any planting bed containing required trees shall have a continuous area of at least 75 square feet for each tree exclusive of bounding walls. Furthermore, each tree located within a planting bed shall be surrounded by a continuous permeable surface measuring at least five feet square. Any lawns or turf grass planting beds shall not exceed six inches above any adjacent walking surfaces.
All planted areas shall either be automatically irrigated or shall consist of species that do not require regular watering.
All planted areas located above subsurface structures such as cellars or garages shall have drainage systems to prevent collection and pooling of water within planted areas.
Street trees are required to be planted in the public sidewalk area adjacent to a zoning lot that contains bonus floor area for public plazas in accordance with Section 26-41 (Street Tree Planting). The length of frontage of the zoning lot for the purpose of computing required street trees may be reduced by 50 feet for each street intersection fronted by the zoning lot. If the Department of Parks and Recreation determines that the tree planting requirements of this paragraph are infeasible, the number of required street trees that cannot be planted shall be planted in accordance with the off-site tree provisions set forth in Section 26-41 or within the public plaza.