soil composition that should be emulated . Utility lines should be identified prior to excavating the site . Property owners or contractors should contact # 811 to make a request for utility lines to be identified . Installation
RAIN GARDENS
Begin by removing 8-10 inches of soil from the rain garden site and placing it along the edges . This should be conducted in a manner to leave a natural bowl with a subtle , sloping berm located downstream away from where stormwater is introduced . The native soil removed and placed along the edges will be used in later steps to form a berm around the downstream perimeter . The inside of the bowl should also be gradually sloping downstream .
Next , a mixture of native soil , sand , and compost should be placed back into the bowl . It is recommended to incorporate a 1:2 mixture of added sand and compost to the native soils removed from the bowl . Coarse sand improves stormwater percolation into the soil and topsoil helps to establish plants installed in the rain garden . Soil amendments should be based on the dominant soil present on site . For most areas on Kiawah Island , the amended soil would generally be around one part native soil ( fine sandy loam ), one part compost , and two parts added sand . Two to three inches should be reserved in the garden for the addition of hardwood mulch . The end result should be a 5-inch high by 12-inch wide berm along the downstream perimeter . In the most downstream area of the berm , a depression in the berm should be created and filled with stones to allow overflow and prevent flooding the garden .
Native plants should be placed throughout the garden with compost added to the entire planting area to help retain moisture and provide a gradual source of nutrients . Finally , a layer of mulch should be placed on top of the exposed soil to prevent erosion and provide additional absorption of water . A double to triple shredded hardwood bark mulch is recommended ; avoid pine straw or bark since these materials will float during a rain event . Cedar mulch is preferred . Native plants are highly recommended to be placed in rain gardens due to their suitability in the local environment . Rain gardens are more often dry than wet , the plants in the rain garden will experience long periods of dry conditions as well as periods of inundation . Native plants have adapted to these conditions in South Carolina . Natives also produce deeper roots in comparison to turf grass . These roots hold onto the soil to prevent erosion and increase the uptake of water from rain garden soils . The following native plants are recommended for inclusion in rain garden designs :
Shrubs Inkberry ( Ilex glabra ) Yaupon holly ( Ilex vomitoria ) American Beautyberry ( Callicarpa americana ) Southern Wax Myrtle ( Morella cerifera ) Dwarf palmetto ( Sabal minor ) Saw Palmetto ( Serenoa repens ) Common Elderberry ( Sambucus canadensis ) Buttonbush ( Cephalanthus occidentalis ) Virginia Sweetspire ( Itea virginica ) Sweet Pepperbush ( Clethra alnifolia ) Swamp Azalea ( Rhododendron viscosum ) Spicebush ( Lindera benzoin )
Grasses and Sedges Blue Flag Iris ( Iris versicolor ) Blue-eyed Grass ( Sisyrinchium angustifolium ) Switchgrass ( Panicum virgatum ) Spider Lily ( Hymenocallis caroliniana ) River oats ( Chasmanthium latifolium ) Bushy bluestem ( Andropogon glomaterus ) Little bluestem ( Schizachyrium scoparium ) Maritime Bushy Bluestem ( Andropogon tenuisphatheus ) White-topped sedge ( Rhynchospora colorata ) St . Augustine Grass , uncut ( Stenotaphrum secundatum ) Muhlygrass ( Muhlenbergia capillaris )
Perennials Scarlet Sage ( Salvia coccinea ) Goldenrod ( Solidago spp .) Dotted horsemint ( Monarda punctata ) Blue mistflower ( Conoclinium coelestinum ) Butterfly milkweed ( Asclepias tuberosa ) Swamp milkweed ( Asclepias incarnata ) Aquatic milkweed ( Asclepias perennis ) Southern saltmarsh fleabane ( Pluchea odorata ) Eastern Rose Mallow ( Hibiscus moscheutos ) Dotted Smartweed ( Persicaria punctata syn . Monarda p .) American Germander ( Teucrium canadense ) Ironweed ( Vernonia noveboracensis ) Golden Canna Lily ( Canna flaccida ) Cardinal Flower ( Lobelia cardinalis )
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