When it rains on our increasingly developed land, runoff and associated pollutants negatively impact our waterways. The native forests and other natural habitats that hold soil in place and filter storm water have been removed over the years, replaced by housing and communities. Impervious surfaces, such as asphalt and concrete walkways and compacted lawns, prevent water from percolating through the ground, unlike natural ecosystems, which allow rain to filter through soils, roots and plants in our forests, meadows and wetlands. A constructed rain garden can act as a living sponge to take up that first inch of rain that carries much of the pollutants washed from hardscapes of impervious surfaces. A rain garden is easy to make and can be a beautiful addition to the home landscape. It will hold and filter storm water on site and cut the volume of water that is lost as well as trap pollutants that otherwise make their way into our streams and rivers.
A rain garden is a low-maintenance garden, approximately six inches below the surface, on level or slightly sloping ground. It can either dry quickly within hours of a rain event or be marsh-like, holding water for several days. Rain gardens are not to be confused with retention ponds that act as water storage basins without plants. A rain garden can be filled with native plants that tolerate both wet and dry conditions. This type of plant is generally deeply rooted so it can take flooding water but succeed in drier periods as well. Natives are beneficial, as these plants support our ecosystems. Because rain gardens don't need synthetic chemicals to survive, they will save money and make your yard a healthier place. Rain gardens can be beautifully planted with perennials, grasses, shrubs and trees.
If properly designed, rain gardens do not attract mosquitoes. Mosquito eggs need as little as 24 to 48 hours to hatch, but the insects continue to live in and rely upon water to survive during the larval and pupal stages which last for another 3 to 10 days. The precise length of each stage depends upon temperature and species of mosquito. Rain gardens typically drain within 6 to 24 hours, allowing a relatively safe margin of time.
Soils with good drainage are a must. After a rainfall, check water flow from your house to see where the water easily percolates. As a test, dig a hole 6 to 8 inches deep and fill the hole with water; it should drain within a day (24 hours).
Avoid creating a rain garden over a septic field (it could overwhelm the drainage system) or where water already collects, which probably indicates poor drainage. Do not disturb established trees. Locate the rain garden in the vicinity of the home's downspouts but at least 10 feet downslope from the foundation. If you have several downspouts, it may be possible to make one large rain garden, although you will need long extensions. Or you can create multiple rain gardens for multiple spouts.
If your rain garden isn't large enough to handle the runoff from your downspout, allow it to overflow onto your lawn; however, don't let it overflow onto your neighbor's property.
Consult a landscape professional for rain garden design, as field conditions influence storm water management.
For the first two years, as the new plants are established and especially during summer droughts, you will need to water weekly and deeply. Weeding and mulching will be necessary until your garden is established.
A Guide to Native Plants of the New York City Region by 
Native Plants of the Northeast by 
