:Shredded woody material or leaf compost used as a top dressing over vegetation beds that provides a source of soil nutrients and helps retain soil moisture; in bioretention cells and dry swales the surface mulch layer provides pollutant removal and improves growing conditions for the selected plants; shredded hardwood bark has been found to work best as it is less likely to float. | :Shredded woody material or leaf compost used as a top dressing over vegetation beds that provides a source of soil nutrients and helps retain soil moisture; in bioretention cells and dry swales the surface mulch layer provides pollutant removal and improves growing conditions for the selected plants; shredded hardwood bark has been found to work best as it is less likely to float. |