Vegetation is used throughout the bioretention site to remediate introduced stormwater , prevent erosion , and provide aesthetic appeal . A landscape design plan outlining the placement vegetation should be created for all bioretention projects by a qualified landscape architect , botanist , or qualified extension agent . The plan should include a mixture of plant species that are tolerant to wide fluctuations in soil moisture content and saturated soils , as well as drought and salinity conditions . Native plants are highly recommended to be placed in bioretention areas due to their suitability in the local environment . Native grasses , perennials , shrubs , and small to medium-sized trees can be incorporated within the planting schedule for bioretention areas .
BIORETENTION AREAS
Native grasses and perennials are highly recommended as they provide deep root systems which stabilize the soil , tolerate local environmental conditions , and attract pollinators . Provided there is a biodiverse mixture of species , they can be used to create an attractive , low maintenance native grass or wildflower meadow . These should be planted in clusters 1.0 to 1.5 feet apart and staggered . Shrubs of the same species in clusters 10 feet on-center , avoiding placement near the inflow and outflow points . Trees should be planted along the perimeter at a density of one tree per 250 square feet , avoiding placement directly above or near underdrains .
Slow growing turfgrass can be used , but should be slow growing , provide thick dense cover , tolerate the expected moisture conditions ( dry or wet ), not require frequent mowing , and have low nutrient requirements . St . Augustine grass ( Stenotaphrum secundatum ) is a native turfgrass to consider in this regard , as it is found naturally on Kiawah Island and maintains consistency with nearby residential and natural landscapes . Charleston County provides a list of suitable native plants in their Standards and Procedures Manual in regards to bioretention areas . The section on rain gardens provides a general list of additional native plants suitable for bioretention sites . Sites near roads and other public rights-of-way should take public safety and human intervention of the site into consideration when selecting the appropriate plants for long-term functionality and resilience . Figure 14 and Figure 15 show cross sections of properly constructed bioretention systems .
Figure 14 . General cross section of a bioretention area with underdrain adapted from Charleston County ( 2017 )
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