While they may seem just like pretty little front-yard flower beds, rain gardens function like mini forests by soaking up and filtering rainwater runoff, usually from a downspout, before it runs down oily streets and reaches natural waterways. Because details about size, soil mixture, and plants depend on local conditions, university extension programs are developing tailored advice for many regions. But here are the key components.
Inlet: Roof runoff is channeled into a buried pipe that carries water into the rain garden.
Ponding Depth: The saucer-shaped basin is designed to hold 6 to 12 inches of rainwater during a storm.
Overflow: A gravel-filled trench collects and disburses water, should the garden overfill.
Mulch: A 3- to 4-inch-thick layer of mulch helps trap moisture.
Soft Soil Mix: A blend of compost and native soil (or sand) absorbs and filters runoff.