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Rain Gardens Can Help Prevent Water Pollution

May 04, 2018

By Ryan Trares - Daily Journal

In a park featuring fanciful play equipment and a splash pad, the most useful and fascinating feature may be a pair of well-placed depressions in the ground.

To go with the slides, swings and other recreational features at City Center Park in Greenwood, planners also laid out a set of rain gardens at the periphery of the park.

The unique gardens catch rainwater as it runs off the parking lots and other walkways, filtering it through the soil before pollutants can make it into rivers and streams.

{One of the rain gardens at City Center Park in Greenwood was built on the edge of the playground. The carved out depression serves as a holding pen for stormwater that runs off the paved pathways and other areas impervious to water, and native Indiana plants help the water absorb into the ground, rather than running into storm sewers.}

{This rain garden at the Greenwood Public Library is ringed by decorative stone, then filled with native Indiana plants. The depression holds water running off the library's roof and parking lots, allowing it to seep into the ground rather than ending up in storm sewers.}

“It’s something that looks like it’s just part of the landscape, but it’s working hard to filter water, and that prevents pollutants from going in rivers, lakes and streams,” said Kara Salazar, sustainable communities extension specialist for Purdue University.

Conservationists and garden experts are increasingly advocating for “rainscaping” in public spaces and private yards. The all-encompassing land use practices focuses on slowing the flow of storm water into the sewer system. Capturing water in natural features not only keeps pollution out of bodies of water, but uses drought-resistant native Indiana plants for a stronger ecosystem and more attractive landscape.

At its heart, the practice of rainscaping is a simple way to make the land healthier, said John Orick, Purdue master gardener state coordinator.

“Stormwater runoff that may come from roofs or driveways or parking lots, where you have cars parked there or other substances that have collected, the water will take them to our bodies of water,” he said. “Rainscaping diverts that runoff.”

The need for rainscaped yards and gardens has come with the growth that many communities in central Indiana are facing.

Increased development and construction have turned green spaces into streets, neighborhoods and parking lots. The land’s ability to suck up rainwater has diminished.

People have torn out the plants that originally made up the ecosystem and planted grasses instead. Grasses have compact roots that don’t allow rain to seep into the ground.

Instead, water that falls on roofs and paved areas runs into storm sewers. When it does, it picks up motor oil, heavy metals, trash and other pollutants that go into rivers, streams and lakes.

The Environmental Protection Agency estimates that pollutants carried by rainwater runoff account for 70% of all water pollution.

“As we develop more and more, we have more houses with roofs, and driveways and stores with really big roofs and really big parking lots. We have all of these impervious surfaces,” said Sarah Hanson, county extension director. “So when water comes down, instead of being able to reach soil, it ends up down a drain or in a creek and river, taking some really dirty things with it.”

And a large amount of water can come from even a small rain storm.

According to calculations done by the U.S. Geological Survey, one inch of rain equals .62 gallons of stormwater per square foot. So during a heavy rainstorm, that inch of rain on an average household roof of about 1,200 square feet creates more than 740 gallons of stormwater.

That same storm hitting a 350,000-square-foot parking lot creates 217,000 gallons of runoff, which will end up in local rivers or ponds, Orick said.

“There’s a lot of potential there to move pollutants to our bodies of water,” he said. “If we can do something to slow it down — you’re not going to stop it, but if people move it into a place where it can absorb in the ground, you can help protect these bodies of water.”

Rainscaping includes concepts ranging from installing a rain barrel to collect water as it comes down your home’s downspout to putting in pavers or bricks that allow water to seep through cracks in and into the ground.

But rain gardens are the most common and effective kind of rainscaping.

The gardens combine native Hoosier plants and water-holding soils to serve as a holding pen where water can collect and pool into the ground.

Rain gardens have been shown to remove up to 90 percent of nutrients, fertilizers and chemicals from stormwater runoff. The gardens absorb 30 percent more water into the ground compared to turf lawns, according to the Environmental Protection Agency.

“It’s a way we can all do our part to influence water quality, but it’s pretty easy to do once you know how to do it,” Salazar said. “It’s not a one-size-fits-all to help with water-quality improvement. But if we have lots of practices on the ground and a lot of people knowing about the importance of those practices, it can have a big impact.”

On May 15 and 16, specialists with Purdue Extension will gather in Franklin for a special workshop focusing on rainscaping. They will learn about the benefits of rain gardens, how to create and maintain the features, and touring existing examples of rainscaping around the county.

At the close of the program, they’ll help create a rain garden outside the office of Purdue Extension Johnson County.

“If we can teach people — anybody from your average person on the street to professional landscapers or people involved with community planning — about rainscaping, then it will make a bigger impact,” Hanson said.

Rain gardens are relatively easy to put into your own yard, though to do so requires some planning, Orick said.

The first step when planning a rain garden is to start at the lowest point of your property, ideally in an area of the yard that naturally collects water after it rains. Locate the rain garden away from your house, but try to make it close to existing gardens.

Typical residential rain garden sizes are between 100 and 300 square feet, and create a dip of 4 to 8 inches in the ground.

The ideal plants for a rain garden are those that thrive in the wet, sometimes cool springs and hot, dry summers of Indiana. These species adapted to the growing conditions locally for thousands of years, and are more resilient.

Sedges and forbes, both common in meadows and forests in the area, are ideal choices. Mosses can help retain moisture.

Dense blazing star, black-eyed Susan and coneflower are all native Indiana plants that offer a nice show of color.

“Choosing the proper plants for the proper place keeps your rain garden vegetated, and maintains the landscape in a way where trees and shrubs thrive, to create a good soil area where water can be absorbed,” Orick said.

Make Your Own Rain Garden

A rain garden is a shallow landscaped area in your yard planted with wildflowers, grasses, shrubs and other native vegetation.

It collects and dissipates the water through soil and plants, and filters rain water from your roof, driveway, sidewalks and lawn before it enters a storm drain or nearby stream. It is dry between precipitation events.

Site requirements

The site must be 10 feet from structures that could be damaged by soil moisture. It cannot be over a septic field.

Ideally, your site should be:

 - Full to partial sun.
 - Quick-draining soil of high organic content.
 - Close to the source of runoff.
 - Flat or bowl-shaped to minimize digging during construction of your garden.
 - An existing site where water naturally pools after rain events, but dries up in 24 hours.

Size calculation

Measure the area of the impervious surfaces, such as roof, concrete or patio, that will drain to the rain garden.

For a rain garden that is 6 inches deep, multiply the impervious surface area by 25 percent to determine the size of your garden.

Observe your garden after rain events. The garden needs to drain within 48 hours. If it doesn’t, make adjustments to the size, overflow area, density and type of plantings.


Call 1-800-382-5544 two days before you dig to locate any underground utilities.

Remove the existing sod or plants.

Dig a 6-inch depression or bowl with a level bottom. Build a small berm opposite the side of water entry using soil excavated from the garden. Allow a low point for water over 6 inches deep to escape.

Some rain gardens may require a subsurface drain pipe. Add organic matter or other amendments to the soil if you want.

Installation and maintenance

Plant choice is important for your site. Install recommended trees, shrubs, sedges, grasses and wildflowers.

Group the same plants together in clumps of at least three for best effect.

Use grasses to help support flowers as they grow taller.

Install and care for plants as you would in other new landscaping. Plants will need to be watered until growth is established. Remember that all plants need water in drought.

Information: Hoosier Heartland Resource Conservation and Development Council

Best Rain Garden Plants

Appropriate rain garden plants

Native trees:

 - Eastern red cedar
 - Hemlock
 - White pine
 - Hackberry
 - Tulip poplar
 - Shagbark hickory
 - Red maple
 - Oaks

Native shrubs:

 - Serviceberry
 - New Jersey tea
 - Spicebush
 - Ninebark
 - Sumac
 - Elderberry
 - Gray dogwood
 - Silky dogwood
 - Virginia sweetspire

Native flowers:

 - Aster
 - Mountain mint
 - Blue flag
 - Autumn sneezeweed
 - Dense blazing star
 - Black-eyed susan
 - White turtlehead
 - Goldenrod
 - Bee balm
 - Phlox
 - Liatris
 - Purple coneflower
 - Summer sweet

If you go

Rainscaping Workshop

What: A two-day program offered by Purdue Extension Johnson County to learn about rainscaping — the practice of designing landscape features to retain stormwater.

When: 8:30 a.m. to 4:30 p.m. May 15 and 16

Where: Purdue Extension Johnson County office, 484 N. Morton St., Franklin.

Cost: Registration is $70 for two days of instruction, lunches and classroom materials. Registration accepted through Sunday.

Information and registration: go to or call (765) 494-6794.


Ryan Trares

Ryan Trares is a reporter for the Daily Journal. He can be reached at [email protected] or 317-736-2727.

© 2018 Daily Journal

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