Rain gardens have emerged as a residential tool for stormwater management in urban systems. Their popularity with home owners, city planners, and developers stems from the coupling of their valued landscape aesthetic with their functionality as infiltration systems designed to treat storm water on site. Rain gardens are designed to disconnect concentrated flow produced from residential structures from regional stormwater infrastructure. Although ample literature exists on the conceptual design of infiltration basins, little experimental research has improved our mechanistic understanding of rain garden function, especially with respect to their function as bioretention systems. Our objective is to experimentally test the mechanistic performance of rain gardens relative to differences in the amount and pollutant concentration of urban runoff and vegetative cover. To test our hypotheses, we constructed 12 experimental rain gardens (6 m2 each) with the following treatments: 3 gardens – bare soil (control); 3 gardens – planted with a typical prairie mix; 3 gardens – planted with traditional bluegrass sod; and 3 gardens – planted with common shrubs. Predetermined amounts of synthetic urban runoff will be applied to test the interaction of plants (prairie vs. sod vs. shrubs) and soil on the infiltration capacity and retention of pollutants. Using concentration differences in the hydrologic budgets, we test the hypotheses that 1) the addition of organic matter to the soil matrix from belowground plant production will increase both infiltration and the retention of pollutants, 2) this effect will diminish with increased levels of urban runoff, and 3) changes in plant productivity will vary among species mix and alter the bioretention of soil pollutants and nutrients. To the best of our knowledge, this poster describes the first quantitative experiment examining the effectiveness of rain gardens.