About Rain Gardens
Rain gardens are a way for homeowners as well as businesses to participate in the reduction of polluted runoff, simply by planting a specialized garden. Rain Gardens are an infiltration technique - 
water is captured in a garden that features native plantings, and the water has a chance to slowly filter into the ground rather than run off into the storm sewer. It is a popular way to reduce non-point source pollution and has been popular along the East Coast for a number of years.
A rain garden traps rainwater and snowmelt and allows them to infiltrate the soil, instead of running over impervious surfaces, like driveways, roofs, roads, patios, and parking lots. Impervious features in the landscape do not let runoff percolate into the soil; water remains above the surface, accumulates, and runs off into rivers and streams.
According to the Environmental Protection Agency, a typical city block generates 9 times more runoff than a woodland area of the same size, because of impermeable surfaces. A rain garden is a natural, on-site means of controlling runoff.
In addition to storing rainwater temporarily, a rain garden filters pollutants carried in surface runoff. Examples of pollutants generated in urban areas include: sediment from development and new construction; oil, grease, and toxic chemicals from vehicles; viruses and bacteria from failing septic systems; road de-icing salts; heavy metals; and nutrients and pesticides from turf management and gardening. The major sources of phosphorus in runoff are lawn clippings and tree leaves left in the streets and gutters. Polluted runoff becomes a water quality issue when it is released directly into lakes and streams without any treatment. Increased pollutant loads can harm fish and wildlife populations, kill native vegetation, foul drinking water supplies, and make recreational areas unsafe.
Rain gardens are designed to direct polluted runoff into a low, vegetated area, where the pollutants can be captured and filtered. The features of a rain garden aid in this bio-filtration process: a shallow basin depth, gentle side slopes, soil that allows infiltration, and vegetation that traps sediment and sediment-polluting runoff. Vegetation shields the soil surface from raindrop impact while the root mass holds the soil particles in place. Improved water quality results from the nutrient removal process as the water and pollutants come into contact with roots and microbes in the soil. Plants, trees, and groundcover absorb up to 14 times more rainwater than a grass lawn.
What about mosquitoes? A rain garden is not intended to detain water for long periods. Ideally, runoff will not be detained for longer than four days, to avoid concerns about mosquito breeding in standing water. Mosquitoes will not survive in wetlands that dry out in less than a week after a summer rain. The development of a mosquito from egg to adult takes 10 to 14 days. A mosquito larva must live in water for 7 to 12 days before maturing to the adult stage.
The Hanson Park Rain Garden was designed to capture water from the sloping garage roof as well as the runoff from the Hanson House and surrounding driveway.
Questions and answers about Rain Gardens
Q: - How do I turn a section of my yard into a rain garden?
A: - Simply dig a shallow depression and plant with native perennials and shrubs
Q: - Don't rain gardens attract a lot of mosquitoes?
A: - No. For reproduction, mosquitoes require a number of days in standing water. Most urban mosquitoes breed in places like junk-piles where there are old tires or tin cans. There is rarely standing water long enough for mosquito reproduction in a well-designed rain garden.
Q: - Can I create a rain garden that doesn't look too wild or messy?
A: - The way to make a rain garden, or any garden, appear 'well kept' is to keep the edges tidy. Tall plants and grasses tend to "flop-over" so if you want a neat silhouette, you will want to stick with short species. To keep native plants from growing too large, remember not to water them!
Q: - What happens to water-tolerant plants when we have a dry spell?
A: - Native plants can withstand a range of weather conditions. Native plants that do well in poorly drained soil will be fine during dry weather.
Q: - How large must a rain garden be to be worthwhile?
A: - Any water that seeps into the ground instead of running into a storm sewer helps water quality. A rain garden of any size has a positive impact