Rain Gardens
A rain garden is a garden which takes advantage of rainfall and stormwater runoff in its design and plant selection . Usually , it is a small garden which is designed to withstand the extremes of moisture and concentrations of nutrients , particularly nitrogen and phosphorus , that are found in stormwater runoff . Rain gardens are sited ideally close to the source of the runoff and serve to slow the stormwater as it travels downhill , giving the stormwater more time to infiltrate and less opportunity to gain momentum and erosive power .
On the surface , a rain garden looks like an attractive garden . It may support habitat for birds and butterflies , it may be a formal landscape amenity or it may be incorporated into a larger garden as a border or as an entry feature . What makes it a rain garden is in how it gets its water and what happens to that water once it arrives in the garden .
Below the surface of the garden , a number of processes are occurring which mimic the hydrologic action of a healthy forest . Soils are engineered and appropriate plants selected for the rain garden . The garden is a small bioretention cell in which stormwater is cleaned and reduced in volume once it enters the rain garden . Nitrogen and phosphorus levels and overall sediment loads in the stormwater are reduced by the action of the plants and growing media on the water . Multiple rain gardens over an area will have a positive cumulative effect on both the volume and quality of stormwater run off .
What does a rain garden cost ?
The cost of a rain garden will vary depending on who does the work and where the plants come from . If you grow your own plants or borrow plants from neighbors there can be very little or no cost at all . If you do all the work but use purchased plants , a rain garden will cost approximately $ 3 to $ 5 per square foot . If a landscaper does everything , it will cost approximately $ 10 to $ 12 per square foot .
Key Terms : BIORETENTION CELL : A shallow planted depression designed to retain or detain stormwater before it is infiltrated or discharged downstream ( also known as a rain garden ).
It might seem easiest to sow native wildflower seed over the garden , but experience shows that seeding a rain garden has its problems . Protecting the seeds from wind , flooding , weeds , and garden pests is very difficult , and the rain garden will be mostly weeds for the first two years . Growing plugs from seed indoors or dividing a friend ’ s plants is much better . If you grow plugs , start them about four months before moving them to the rain garden . When the roots have filled the pot and the plants are healthy , they may be planted in the rain garden .
For more information on how to design and install a rain garden visit : www . lowimpactdevelopment . org
Photo courtesy of : www . apwa . net
For a list of native plants to use in your rain garden , visit The City of Arlington ’ s Forestry website at www . naturallyfun . org 46