How to Build a Rain Garden for Catching Rainwater
A Natural Filter for Stormwater Runoff
A well-designed rain garden is an organic and low-tech method for controlling the runoff from rainstorms and snowmelt. Runoff from rooftops, driveways, patios and other nonporous surfaces is channeled and directed away from buildings and towards a low-lying section of the yard. As the rainwater and snowmelt runoff travels across the lawn and hardscape, fertilizers and pollutants are washed into the rain garden's natural filtration and cleansing system.
Dug into a shallow bowl shape, the rain garden retains stormwater run-off and helps to control soil erosion. The sunken planting beds capture the run-off and hydrate the landscape plants, and any excess water filters down through the soil. The organic cleansing action helps to remove salts and chemical residues before the runoff seeps deep below the surface into the underground aquifers.
Rain gardens are easy to maintain and can attract birds, butterflies, toads and other wildlife into the backyard. The above photo was taken in early summer and highlights the native ferns. Other perennials including Brown-Eyed Susan and Ajuga Bugle plants add colorful blooms, while an Inkberry shrub and a dwarf conifer provide texture and visual interest during the winter season.
Why Assessing Location Is Important
Our property is situated on a hillside, and we get a lot of storm water runoff and snowmelt from the surrounding higher elevations and from the rooftop of our home. The photo (above) was taken in late winter, after this year's snowmelt is gone but before the perennial plants have awoken from their winter slumber.
Located in the lowest section of the backyard, we dug into the bottom of the sloping lawn and directly in front of a berm that forms one side of our little pond. We buried a plastic drain pipe under the lawn and connected the other end of the pipe to the primary downspout for delivering runoff from the roof. A gentle swale sculpted into the lawn helps to steer more of the water runoff from rainstorms and snowmelt away from the house and into the planting bed.
Note: The planting bed at the bottom of the sloped yard is separated from the pond by a berm of soil and rock. Do not let the water runoff drain into your koi pond!
We used pieces of fieldstone and rock to create a border and to define the bed's borders and edges. The fieldstone also helps to disguise and protect the plastic drain pipe from the roof gutters. A few strategically placed rocks in front of the drain pipe opening helps to diffuse the rushing water as it travels downhill from the roof and into the sunken garden. We do not apply any mulch, which would likely wash away from the drainpipe area and into the basin of the planting bed. Instead, a ground cover of Ajuga Bugle plants helps to control weeds.
Between rainstorms, the opening to the drain pipe and its surrounding rock cave is a favorite hangout for a large toad. Other welcomed visitors include insects, wood frogs, chipmunks, garter snakes and an occasional box turtle.
Our rain garden fits well into our landscape, is simple to maintain, looks good and is very effective at controlling large volumes of runoff from the roof and the sloped yard. Planted primarily with native Christmas ferns and Cinnamon ferns, the plants help to control soil erosion on our hillside and act as a natural filter. The captured stormwater runoff soaks the soil and provides plenty of moisture for the ferns before the excess water seeps down into the ground. The water runoff is utilized by the plants rather than washing away into a storm drain.
Even after a significant rainstorm, the planting bed dries out within a day and does not leave any standing water. No standing water means there's no place for mosquitos to breed!
Tips for Creating a Rain Garden
- Select a low-lying area or natural depression. Consider using an area that puddles naturally after a rainstorm or snowmelt.
- Strategically locate an area near a downspout or at the bottom of a natural slope, but position the planting bed at least 10 feet away from the house foundation and other buildings.
- Do not select a site that is over the septic tank or leeching field.
- Avoid digging in areas near underground utilities including gas, electrical and water lines. If in doubt, check your local listings for the "Call Before You Dig" contact information.
- Use hardy native plants that are suitable for planting in both wet and dry conditions. Add a few non-native plants for seasonal variety of height, foliage, texture and blooms. Avoid planting exotic and invasive species.
- Until the plants become established, weed the planting bed often to remove the undesirable weeds. The established and matured perennials will crowd out the weeds, reducing the long-term maintenance needed to keep the rain garden looking good.
Rain Garden at the University of Nebraska
The Benefits of Creating a Rain Garden
- Controlling storm water runoff and reducing soil erosion
- Reducing the amount of runoff that enters the storm drains and municipal water treatment systems
- Protecting rivers and stream from property runoff that contains fertilizers, pesticides and other chemical pollutants
- Filters storm water runoff while replenishing groundwater and aquifer reserves
- Attracts birds, butterflies and other wildlife
- Reduces lawn and gardening maintenance
Do Rain Gardens Attract Mosquitoes?
A common misconception about rain gardens: they are not swampy bogs. A well-placed and properly planted area controls and utilizes the flow of stormwater, however, a well-designed sunken garden is not a bog and it does not stay wet all of the time (no standing water means no mosquitoes). Planted with native perennials, a typical rain garden drains well and dries out within a day or so, filtering the runoff before it enters into the groundwater system.
A Common Misconception
Rain gardens do not attract mosquitoes!
Consider a Rain Barrel
Rain barrels are another option for controlling stormwater runoff. We use a rain barrel to collect runoff from the roof in another area of our yard. Unlike a rain garden that uses the trapped water immediately to hydrate thirsty plants, a rain barrel collects and stores the rainwater for future use. Runoff from the roof is channeled through the gutter and downspout to an inflow point at the top of the barrel. When the barrel is full, an overflow value allows the excess water to escape. A spigot at the bottom of the rain barrel connects to a garden hose, making it easy to use the rainwater when and where it is needed, such as watering container plantings throughout the growing season.
Most rain barrels are essentially large plastic containers. Manufactured kits are easy to install, and are available in a variety of styles ranging from basic utilitarian to decorator models. Size and capacity also vary; 50 to 75-gallon storage capacity rain barrels are commonly available. If more watering capacity is needed, some models can be hooked together through a simple manifold system that delivers rainwater to each of connected barrels.
Do You Have a Rain Garden?
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
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© 2012 Anthony Altorenna