A rain garden is a planted depression that allows rainwater runoff from impervious urban areas like roofs, driveways, walkways, and compacted lawn areas the opportunity to be absorbed. This reduces rain runoff by allowing stormwater to soak into the ground.
Rain gardens are beneficial for many reasons: improve water quality by filtering run-off, provide localized flood control, aesthetically pleasing, and provide interesting planting opportunities. Rain gardens encourage wildlife and biodiversity. A rain garden is a strategy to utilize rain fall to reduce or eliminate irrigation. Rain gardens deal with excessive stormwater runoff without burdening the public storm water systems. Unlike a retention basin, water slowly infiltrates the ground in the days following the rain fall. Since water is not 'stagnant' it reduces the chance of mosquitoes breeding in the collected water.
Plants selected for use in a rain garden should tolerate both saturated and dry soil. Using native plants is generally encouraged. This way the rain garden may contribute to urban habitats for native butterflies, birds, and beneficial insects.
Well planned plantings require minimal maintenance to survive. Trees generally contribute most when located close enough to tap moisture in the rain garden depression, yet do not excessively shade the garden. That said, shading open surface waters can reduce excessive heating of habitat.