For many years, no one gave much thought to the dispersal of rain water unless there was flooding. Recently, however, one of the hot topics in urban landscapes is stormwater runoff and how to prevent it from going into our sewers and eventually into our rivers and lakes. Why? Because such efforts will reduce the amount of pollutants (fertilizers and pesticides) that wash out of our yards with the rain in stormwater runoff. A corollary to that issue is preventing the runoff from inundating neighbors whose property is below ours.
A few weeks ago, I attended a design workshop on that very issue. While some very expensive solutions were offered, I think the simplest is creating rain gardens and bioswales. The two really differ only in configuration. Bioswales are more linear than rain gardens that can be created in almost any shape. The idea is to design an area that will temporarily hold water until there is sufficient time for it to be absorbed into the soil. Rain gardens ideally hold this water for no more than thirty-six hours. This means that the plants chosen for rain gardens must be able to withstand inundation for a short period of time but must also be tolerant of drier conditions that will occur when there is little rain.
In the past, I’ve attended lectures about design and installation of rain gardens that make their creation, I think, unnecessarily complicated, using specially developed soil mixes that will allow the water to drain quickly. However, a five-year study in Madison, Wisconsin showed that small, clay soil, rain gardens on residential properties can also absorb that water when planted with native prairie species, the roots of which penetrate the clay. In fact, one of the hydrologists involved in the study said infiltration rates steadily improved throughout the study, as the long roots of the prairie plants pushed deeper into the subsoil.
Like any other type of landscaping, rain gardens can be attractive or they can look like a collection of weeds. What you get will depend on plant selection and composition that pay attention to differing forms, textures, and colors of flowers and foliage. Creating a viable rain garden entails specific knowledge and I would suggest that you hire a landscape designer to do the design even if you want to install it yourself.
If enough people installed rain gardens, we could change our society from an engineering metric to a gardening metric.