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What Does a Rain Garden Do?
In urban areas, impervious surfaces (like paving and rooftops) prevent rainwater from entering the ground, so it must be collected and discharged. Increased runoff from these surfaces creates excessive peak flows that lead to erosion and water degradation.
This runoff often contains biological contamination, from fertilizer and pet waste to oils from roads and driveways. The cost of conveying and treating this runoff is considerable, which is why an increasing number of public utilities are offering incentives to homeowners who reduce runoff by building rain gardens.
Choosing a Location
Look for existing low points in your yard at least 10 feet away from property lines and houses, but near the impervious surface that's causing the runoff.
The size of your rain garden will depend on local rainfall, the tributary area and the soil type. Poorly draining soils can be amended with mulch, which functions a bit like a giant sponge, holding water where it can be picked up by plants.
Rain gardens fill with water during and after storms. The water percolates into the soil and dissipates through a process called evapotranspiration, a combination of evaporation and the release of moisture from plants.
Still, it is a good idea to plan for water discharge into an area away from buildings. Seasonal pools like this one are a good solution, and they're a valuable habitat for amphibians and other wildlife. These ponds dry up in the summer, so they don't encourage mosquitoes.
Planning Your Garden
Rain gardens come in all sizes. This small rain garden designed by Vinita Sidhu collects the runoff from a garage roof.
Choose a variety of plants to accommodate the different zones within the garden. The lowest points will receive more water and stay wet longer than plants on higher sides.
Native plants that can tolerate both occasional flooding and dry periods are great choices for rain gardens. Your city and state cooperative extensions are likely to have great resources available to help you design your rain garden. The Seattle Public Utilities Rainwise Program is one of many great resources.
Rain gardens are a great way to soften a formal landscape or to provide a transition from formal to natural areas of the landscape. Choose plants that enhance your backyard and create a cohesive look.
Do you have a rain garden? We'd love to see it. Please post a photo below!
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