In certain parts of the country, rain gardens are growing in popularity and that trend is becoming a factor in the health of local environments. And it's a trend in which you can take part.
Nowhere is this more evident than in the east coast’s Chesapeake Bay watershed. The Chesapeake Bay watershed spans more than 64,000 square miles. It encompasses all of the District of Columbia and parts of six states: Delaware, Maryland, New York, Pennsylvania, Virginia and West Virginia.
Nearly 18 million people live in the watershed area. They live in houses, drive on asphalt streets, walk on sidewalks and park cars in large mall parking lots. When it rains, water falls on the impervious surfaces of roofs, parking lots and streets, and funnels into sewer systems that dump into nearby rivers. The Susquehanna, Potomac, Rappahannock, York and James rivers all connect to the Chesapeake Bay.
When it rains, pollutants like road oil and other chemicals wash down storm drains and into the watershed where large populations of crabs, oysters and other sea creatures live. These fish and crustaceans feed the people who live in the watershed area and support a large watershed-based fishing and tourism economy.
That’s why there’s such a huge push in the region, and in many other places around the country, for new construction or renovation projects to include an on-site system that captures rainwater and filters it before releasing it down into the water table. These systems are known by the much more consumer-friendly term of “rain gardens.”
“A rain garden, as we define it, would be a garden with soil and plants where stormwater or rainwater is diverted,” says Eric Drenner, president of E-Landscape Specialty Solutions, a design-build firm based in Davidsonville, Md.
“That garden uses the soil mix and the plants to filter out contaminants whether they are chemicals or road oil or heavy metals. The water is filtered through the soil. The rain garden allows the water to dissipate through the soil so that we are not relying on water inlets or drain inlets that just dump into our waterways without any kind of treatment.” Drenner has designed and built “a couple hundred” rain gardens in the Chesapeake Bay watershed over the past decade.
Right now, Drenner’s company is working on a low-income housing project in the District of Columbia that, according to regulations, is required to have an onsite rain garden system that can contain and process a rain event of up to 1.25-inches of precipitation. The approximately 5-acre project will need more than 20 rain gardens on the property to handle the job. The goal, Drenner says, is to “alleviate the pressure put on stormwater management systems by having these properties handle and manage their rainwater runoff.”
Design and construction of a rain garden, Drenner says, runs from $75 to $95 per square foot retail to the customer.
In the Pacific Northwest, rain gardens are a growing trend. A campaign by Washington State University sets a goal of 12,000 rain gardens installed in the Seattle/Puget Sound area by 2016 in order to soak up 160 million gallons of polluted runoff.
Portland has an initiative called Green Streets that converts curbsides into rain gardens. The retrofit uses landscaped curb extensions, swales, planter strips, pervious pavement and street trees to intercept and infiltrate stormwater before it reaches storm drains.
Portlanders, now familiar with the rain garden concept, have embraced the structures, says Ben Bowen, a landscape designer with Ross NW Watergardens, based in Portland. He says the average home lot in Portland is 5,000 square feet, requiring a rain garden of about 100 to 150 square feet. The rain gardens are considered “desirable and responsible to have on your property.” Although his company has been building rain gardens for about 15 years, they have become “much more common over the last five to six years,” Bowen says.
In Fairfax County, Va., local stormwater regulations limit a property’s percentage of impervious surfaces including rooftops, driveways and even swimming pools, says David Marciniak, owner and lead designer of Revolutionary Gardens in McLean, Va. “If what you’re proposing exceeds (that percentage), you may want to look at solutions like permeable paving and rain gardens.”
A rain garden requires soil sandy enough to allow infiltration and plant material (usually native plants) that can handle periods of dryness followed by cycles of 24 to 48 hours of wetness while the water drains. “When they first came out, rain gardens were not embraced because of poor plant choice,” Drenner says.
To figure out the right mix for any region, Marciniak says “in most cases, the local area will have a stormwater best management practices guide. I’ll crib off what they use there and use the local recommendations.”
For professionals wanting to add rain gardens to their mix of services, learning how to properly design and construct them is becoming easier. More and more university extension offices offer workshops for pros and at least two programs, one at Rutgers University in New Jersey and one at North Carolina State University, offer professional certification.
“Specifying of rain gardens is becoming more and more common. Done improperly, they become a waterlogged mess that kills everything in them. Done correctly, they're pretty awesome,” Marciniak says. “I think it’s a huge opportunity for contractors willing to explore the idea to a get handle on plants that will like wet feet. If 90 percent of these look awful and you’re among the 10 percent that make them look amazing, that’s a fantastic marketing tool right there.”
Rain garden resources
- North Carolina State University Residential Rain Garden Certification for Professionals
- Washington State University rain garden workshops for professionals
- Rutgers University Rain Garden Certification Program
- St. Louis, Mo., rain garden program
- “Rain Gardening in the South” by Helen Kraus and Anne Spafford
- City of Portland, Ore., How to Build a Residential Rain Garden
- 12,000 Rain Gardens in Puget Sound program
The author is a freelance writer based in Mount Vernon, Wash.