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Some plants work well in rain gardens in coastal North Carolina

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By Master Gardener, Brunswick County Extension

Rainwater picks up pollutants from our lawns, gardens, roads and takes them into the rivers and bays. Rain gardens are a beautiful way to cleanse the environment of pollutants and keep our rivers and bays cleaner for its inhabitants, our cherished sea life.

Rain gardens are raised beds in reverse. They are mirror images of conventional gardens that are planted high; rain gardens are concave planted in shallow basins. 

A rain garden can be a real problem-solver for a perpetually soggy area where grass will not thrive but a rain garden’s most important job is to capture and cleanse runoff water of pollutants as the rainwater soaks into the soil of the garden. The innocent, seeming water running down the gutter during storms, carries with it pet waste, fertilizers, insecticides and herbicides from lawns, and gasoline and oil leaked from cars, as well as traces of heavy metals. 

Water that once soaked into the ground now runs on top of roads and other impervious surfaces often heading straight into nearby streams, lakes, creeks, rivers and bays.

Pioneered in Price George’s County, Md., rain gardens are designed to merge two important goals: aesthetics and water quality. Rain gardens also known as bio-retention areas are intended to be landscaped areas that treat storm water runoff. Water is directed to the garden by pipes, swales or curbs openings. 

The shallow depression planted with water tolerant plants temporarily holds water rather than shedding it away. The trees and shrubs growing in rain gardens are water tolerant, rather than water loving. Rain gardens can vary in size. They can be installed in a corner of your lawn, placed along the edges of roads, or put in the medians of parking lots. The size and design of the rain garden depend on the area that drains to it and the type of soil in which the garden is placed.

To create a rain garden, first identify a spot downhill from a downspout or driveway that will become your natural spot for collecting runoff. Second, test the absorption rate of the soil there by digging an eight-inch hole with vertical sides. Fill with water, then refill again in one half hour; then after four hours, measure how far the water level has subsided. Multiply this number by six to determine how many inches of water the soil will absorb in 24 hours, and excavate a saucer-shaped basin that deep. 

The third step is to rototill the bottom of the basin, working in an inch or two of compost or sphagnum peat. The fourth step is the fun part; you get to set in plants that will thrive within the rain garden. Tuck in the plants with two inches of organic hardwood mulch, and irrigate during prolonged dry weather through the first growing season.

Plants that work well in rain gardens in the coastal South are: New England Aster, Spotted Joe Pye Weed, Sneezeweed, Torrey’s rush, Prairie blazing star, Cardinal flower, Great blue lobelia, Wild bergamot, Marsh phlox, Mountain mint, Green bulrush, Stiff goldenrod, Culver’s root and Golden Alexander. Trees and shrubs that enjoy the diverse conditions of the rain garden are: Box elder, Red maple, Red chokeberry, Redbud, Sweet pepperbush, Ti-ti, Strawberry bush, Green ash, St. John’s wort, Dwarf yaupon, Grey owl red cedar, Sweetbay magnolia, Wax myrtle, Longleaf pine, Loblolly pine, Cherrybark oak, American elderberry and Scull cap (ground cover).

Rain gardens are attractive best management practices because they can improve environmental quality while meeting landscape requirements. Rain gardens appeal to homeowners as well as developers as they can be constructed in both residential and commercial areas. Try one and see how well it can work for you.

For more information about the plants listed above, send your gardening questions or comments to: Brunswick County Master Gardener Column, P.O. Box 109, Bolivia, NC 28422, or call 253-2610. Enclose a self-addressed, stamped, envelope if requesting information or a reply. Answers may be printed in this column. Visit the Brunswick County Center of the North Carolina Cooperative Extension Service website at www.ces.ncsu.edu/brunswick/ or access the site through the Brunswick County Government online website at www.brunsco.net.