As more houses are built in undeveloped areas, storm water runs into storm sewers that carry it away from the local water table and the area that fills it. This area, called an aquifer, cleans and stores water for local water supplies. Rain gardens full of strong-rooted native plants are naturally adapted to the growing region and hold water back so that more of it soaks into the aquifer.
Native trees are successful because they spread out roots that collect as much water as the tree needs. Trees may be chosen for aesthetics or shade and may be planted in or adjoining the rain garden. Most native trees have wide, shallow roots that will not allow many other plants to flourish under their branches. Choose tall red maples, green ash, willows, bald cypress and Nutall oak. River, swamp or paper birches are native in different areas. Use evergreens such as white Atlantic cedar, red cedar, Southern magnolia and longleaf pine. Pin and Red oaks live on the margins of wetlands; like the red maples, they may be too large for your rain garden itself but can live near it and contribute to its task of slowing down runoff. When choosing trees, check to confirm that the tree you're considering is a native species in your area.
Use shrubs and small trees that grow multiple trunks to provide structure and background for perennials and biennial herbaceous plants. Native shrubs include azalea, red twig dogwood, ninebark and rhododendrons. Serviceberry, winterberry holly, highbush blueberries, inkberry and chokeberries produce berries that attract wildlife. Northern bayberry, Virginia creeper and Prairie rose gentian all give clues to their origins. Swamp rose mallow is also called the pink swamp hibiscus; it has several native cousins. Vines like wild clematis, pipevine and American bittersweet add height to a garden on a trellis or tree.
Rain gardens are not wet or dry all the time. When it rains, water may stand in them for several hours, and they may dry out for weeks at a time in the summer. Native plants that grow in wetlands or floodplains make perfect rain garden candidates. Chart the mini-climates within your rain garden and choose natives that will thrive in your man-made wetland. Wild columbine and Jack-in-the-pulpit are woodland plants that like shade and moist soil. Swamp milkweed thrives in wet soil. Cardinal flower, Joe Pye weed, black-eyed Susan and liatris are widely-adaptable natives. Phlox varieties, both perennial and annual (Drummond), grow well in rain gardens. Echinecea, including Topeka and Tennessee, sanguine, Eastern and pale purple coneflowers, as well as one yellow coneflower, bloom well in rain gardens. One Southern coneflower is not a member of the Echinacea family; the bi-color annual clasping-leaf coneflower is an Aster. According to the Lady Bird Johnson Wildflower Center, it is a native of ditches, ravines and depressions, the native counterparts of the rain garden.