What is a rain garden?
A rain garden is a garden of native shrubs, perennials, and flowers planted in a small depression which is generally formed on a natural slope. It is designed to temporarily hold and soak in rain water runoff that flows from roofs, driveways, patios or lawns. Rain gardens are effective in removing up to 90% of nutrients and chemicals and up to 80% of sediments from the rainwater runoff. Compared to a conventional lawn, rain gardens allow for 30% more water to soak into the ground.
A rain garden is not a water garden. Nor is it a pond or a wetland. Conversely; a rain garden is dry most or the time. It typically holds water only during and following a rainfall event. Because rain gardens will drain within 12-48 hours, they prevent the breeding of mosquitoes.
Why is rain water runoff a problem?
Every time it rains, water runs off impermeable surfaces, such as roofs or driveways, collecting pollutants, such as particles of dirt, fertilizer, chemicals, oil, garbage and bacteria along the way. The pollutant-laden water enters storm drains untreated and flows directly to nearby streams and ponds. The US EPA estimates that pollutants carried by rainwater runoff account for 70% of all water pollution.
Rain gardens collect rainwater runoff, allowing the water to be filtered by vegetation and percolate into the soil recharging ground aquifers. These processes filter out pollutants.
What makes a suitable site for a rain garden?
*The ideal rain garden site meets the following criteria*
- The site is fed by one or two down-spouts
- Soil tests show the site does not have heavy clay soils (conduct a ribbon soil test)
- infiltration tests show the site infiltrates water one-half inch per hour or more
- The water table is at least 2 feet from the surface at the shallowest
- The slope of the site is not more that 12%
- The site is at least 10 feet from buildings with basements
- The site is not over any utilitites (contact your local diggers hotline)
- The site is not over or near a septic tank, drainfield, or wellhead
- The site does not interfere with any trees. If there are trees in the area, make sure they can handle wet soil conditions for lengthy periods of time.
*If the site that you have chosen does not meet all of the above criteria, it does not necessarily mean that a rain garden cannot be established there. Speek with a professional landscaper to review your options.*
What is the average size of a Rain Garden?
A rain garden should have an area about 20% the size of the roof, patio, or pavement area draining into it. A typical rain garden for a residential home or small building is generally between 100 and 400 square feet. Regardless of the size, big or small, each rain garden can make an impact.
What benefits do rain gardens provide to my community?
- Improves water quality by filtering out pollutants
- Aesthetically pleasing
- Preserves native vegetation
- Provides localized storm-water and flood control
- Attracts beneficial birds, butterflies and insects
- Easy to maintain after establishment