A rain garden is intended to prevent water running off the roof of your house straight into the main drains. Instead the rain garden will act like a sponge to absorb the water back into the soil. The main benefit is to reduce the amount of pollution flowing into nearby streams and rivers through the storm drains. Jeanne Huber writing in This Old House magazine explains how you can create a rain garden with pictures showing each step.
During a downpour at a typical house in many municipalities, water gushes out of downspouts, across lawns treated with pesticides and fertilizers, into an oily street, and, finally, down a storm drain that dumps that pollution along with the water into a stream, river, or bay. By building a rain garden, you can divert your gutter water into an attractive planting bed that works like a sponge and natural filter to clean the water and let it percolate slowly into the surrounding soil. Installing a rain garden isn’t difficult if you’re willing to dig or you bring in machines to help. Ask your local Cooperative Extension Office for specifics about soil mix, garden size, and plants for your area. Then you’re ready to build.The plants and amended soil in a rain garden work together to filter runoff. Generally, a rain garden is comprised of three zones that correspond to the tolerance plants have to standing water; the better a plant can handle “wet feet,” the closer it is placed to the center of the garden. Whenever possible, shop for native and drought-tolerant plants, keeping in mind that parts of a rain garden remain wet for long periods of time, while others are drier. Zone 1, the centermost ring of the rain garden, should be stocked with plants that like standing water for long periods of time, such as Lady fern (Athyrium filix-femina). The middle ring, Zone 2, should have plants that can tolerate occasional standing water, like Snowberries (Symphoricarpos albus). The outermost ring, Zone 3, is rarely wet for any length of time and is best planted with species that prefer drier climates, such as western bleeding heart (Dicentra formosa).