Rain Gardens Provide A Healthy Corrective To Runoff Flooding

University Place: How Master Gardeners Use Landscaping To Alleviate Excess Water And Foster Native Plants
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Rain gardens require ample sunlight and should be placed at least 10 feet away from a structure

A deluge of flood warnings start cell phones buzzing around Wisconsin whenever heavy rains soak the state. While flooding can threaten homes along waterways, even landlocked properties experience water accumulation during heavy or sustained rainfall. But a strategically placed rain garden can mitigate excess water and add visual interest to a property.

A rain garden is a shallow depression filled with long-rooted grasses and other plants that soak up rainwater flowing from roofs, pavement or other impervious surfaces. Kris Pfeiffer, a Master Gardener in Racine, was faced with a shattered sump pump line that imperiled the foundation of her house. She installed a rain garden to help address the problem, and shared the process of how she created it with a group of colleagues in the University of Wisconsin-Extension Master Gardener Program. Her talk given on April 25, 2016 was recorded for Wisconsin Public Television's University Place.

"When life gives you lemons, you make lemonade. When life gives you a broken sump pump line, you make a rain garden," Pfeiffer said. "I like that I'm not dumping water into the storm sewer system, where the water picks up all the pollutants and herbicides and grass clippings and everything, and drags it down into the local waterways."

Pfeiffer followed a guide published by the Master Gardener Program and the Wisconsin Department of Natural Resources, and used a "Plant Finder" database created by the Missouri Botanical Garden to select 204 native plants, one for each square foot of her garden. She stressed the importance of choosing local vegetation, citing the dependence insects and birds have on plants like fox sedge, milkweed and false indigo for food and nesting.

While these gardens are designed to collect rainwater, Pfeiffer said they do not provide a breeding ground for mosquitoes, whose larvae require a prolonged habitat of standing water to mature. The plant composition of a properly designed rain garden will dispel collected water in two to three days.

Margie Hannes, who along with Pfeiffer is a member of the Racine Kenosha Master Gardener Association, likewise spoke about her rain garden and how it grew into a mature stage. She installed it to prevent flooding on a neighboring property, and it was funded with a grant from the Root-Pike Watershed Initiative Network.

"The water would swell into my property, and over to the neighbor in the west," Hannes said. "We can't change the natural swell of it, so we figured out if we put a rain garden in, that would help stop some of it."

Hannes found her garden grows a little larger with each passing season – from a starting size of 75 square feet to 84 square feet in her spring 2016 measurement – giving her room to plant more New England aster, Torrey’s rush and prairie cordgrass, among others. She warned that the prairie grass, with roots up to 20 feet long, is an aggressive grower and can overtake other plants.

Key Facts

  • Rain gardens are best sited in locations with exposure to partial to full sunlight. They should also be placed at least 10 feet from a building's foundation or other structure to avoid damage from standing water.

  • The size and depth of a rain garden depends on slope of the surrounding landscape, as well as the square footage of the areas draining into it. Most residential rain gardens are four to eight inches deep, so the location of lines for utilities like power and gas should be determined before digging. Additionally, rain gardens should not be placed above or near septic systems.

  • Adding two inches mulch to the surface of a rain garden after planting will help discourage weeds, and help plants retain moisture during dry parts of the growing season. When rain does not supply sufficient water accumulation, gardens should be watered to a depth of one inch each day.

  • The speed at which a rain garden functions depends on soil composition. Loose, sandy soil drains faster than thicker clay. The type of soil present in a proposed rain garden also determines the ideal plants for the space.

  • Regulations impacting rain gardens can vary by municipality or neighborhood. Consulting with local governments, homeowners associations and neighbors prior to the start of a project can help avert future conflicts.

Key Quotes

  • Pfeiffer on the expense of planting a rain garden: "Plants were the biggest expense in my rain garden. I planted one native plant for every square foot, so there's 204 native plants in my rain garden… at a cost of just over $770. Smaller garden means smaller expenses… if you're gonna go with renting equipment, that is also gonna increase the cost of your rain garden. You can do it by hand if you have the time and the energy, or you can take a shorter cut and use equipment to help you get there faster."

  • Pfeiffer on the value of native planting and identifying non-natives: "The native plants are designed here and the birds and insects have learned to rely on these plants for their food sources and for their nesting. If you are working with cultivars or with ornamentals, they look beautiful. There's lots of them that look very similar to the natives, but... those slight variations that they have in nectar, in bloom, in when things bloom, the thorns, the leaves – all of those things can play havoc on the natural ecosystem… If you're looking to plant native plants, look closely at the scientific name and avoid the plants who have the third word in quotes. That's usually an indication that you aren't planting something that's native."

  • Pfeiffer on the benefits native plants offer wildlife: "I have lots of insects and butterflies and birds. There's always something going on in my native garden and in my rain garden, and it provides a valuable habitat for the birds, the butterflies and the beneficial insects that live with us."

  • Hannes on the ongoing maintenance her rain garden requires: "We have all our downspouts diverted into the rain garden by drain tiles, and we need to keep the debris out of the back channel because of the downspouts running in. I'm constantly back there cleaning that out so the leaves don't clog it up. When it fills up with too much water in the spring, we sometimes have to release the berm and break it apart so that some of that water can come out."

  • Pfeiffer on her garden's appearance in the off season: "I left everything stand[ing] in my garden. I like the winter interest, the birds. There were parties in my front yard all winter long of different birds coming through and picking through the seed heads. It was so much fun to watch who was in the garden, even in the winter… It's personal preference how much maintenance you do in the fall or during the spring."
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