There has recently been increased interest in the use of rain gardens to reduce water runoff in Indiana and nationally. A rain garden is a specially constructed area with a berm, planted with various plants, and designed to capture rain water from the roof of a house or building. Rain gardens fill with water after a significant rainfall event and the water slowly filters through the soil rather than running directly into a storm drain. The idea is that by capturing the rain water, it is possible to reduce storm water runoff and help protect the environment by recharging ground water, reducing flooding, etc. More information about rain gardens and protecting water resources can be found at the following link http://www.ces.purdue.edu/extmedia/FNR/FNR-256.pdf .
Traditionally, turfgrass is not often recommended for rain gardens and instead native plants and wild flowers are commonly planted in these gardens. Some articles even state or imply that turfgrass on lawns has a negative impact on water quality. The research on this subject states just the opposite. Turfgrass is often used on farms and in urban areas to trap sediment and reduce runoff in efforts to improve water quality. Research on turfgrass systems states that there is less runoff and sediment loss after rainfall from lawn areas compared to bare soil, shredded mulch and simulated urban forests, and that there is less runoff from turf than from prairie vegetation and crops. Turf affects the overland flow process of water to such a degree that runoff is from lawns insignificant and infrequent. Pesticide and nutrient concentrations in runoff from turf are low because most chemicals applied to turfgrass are trapped within the leaf, thatch and rootzone areas and do not contaminate water supplies. Despite some of this evidence, turf is not commonly used in rain gardens. Recent research out of the University of Wisconsin-Madison has documented the successful use of turf in rain gardens.
The following is a summary of some research at the University of Madison-Wisconsin. Their findings were “Urbanization has led to an increase in impervious surfaces that indirectly feed surface waters with potentially pollutant-laden water and reduce groundwater recharge. By using a landscaped garden in a shallow depression, a rain garden, that receives storm water from a rooftop, homeowners may be able to decrease the negative impacts that rooftops have on urban waters. This study investigated whether the presence of berms, type of vegetation, or combination of the two decreases runoff and increases groundwater recharge. Treatments included: 1) Kentucky bluegrass with a berm, 2) Kentucky bluegrass without a berm, 3) native mixture with a berm, and 4) native mixture without a berm, and they were planted in October 2005. Each plot had a separate rooftop, lysimeter, and runoff weir. Runoff and leachate volumes and samples were collected as appropriate. All samples were analyzed for NO3, NH4, total P, and dissolved P. Runoff samples were also analyzed for total suspended solids. After one year of data collection, both bermed treatments significantly reduced the amount of runoff and increased the amount of leachate when compared to both unbermed treatments. The unbermed native mixture treatments produced over two times more runoff than did the unbermed Kentucky bluegrass treatments. Water quality and use were similar for turf and native plants. These results indicate that the presence of a berm appears to be the major determining factor behind rain garden effectiveness, regardless of vegetation type.” Jacob Schneider, John Stier, and Doug Soldat, University of Madison-Wisconsin – originally published in Golf Course Management – March 2008.
Hopefully, this research will encourage more to use turf in rain gardens. The beneficial effects of turfgrass on water quality have been documented in the past and now research confirms that they can successfully be used in rain gardens to reduce runoff and increase the amount of water naturally filtered through the soil.
Aaron Patton, Turf Extension Specialist