Bioswale Grasses

Turf Grass

• The simplest type of bioswale is a channel planted with turf grass. These channels are similar in form to a drainage ditch, but their slopes are shallower, allowing water to move through them more slowly. Turf grass is an inexpensive option for bioswale planting, but it doesn't slow the flow of water as much as other plantings and therefore doesn't allow contaminants to settle out of the water as readily. Infiltration of the runoff into the ground water is also not substantial, meaning that a turf grass bioswale does not help to quickly return runoff into the water cycle. Turf grass channels are best used to direct runoff to other water treatment structures.

Native Grass Sod

• In 2008, Montana State University conducted a study for the California Department of Transportation to determine what types of native grasses would function best in a sod mixture to be used in bioswales and on slopes along highways. The sod mixtures developed for the study included native species such as creeping wildrye, purple needlegrass, Sandberg's bluegrass, California meadow barley, squirrel tail, California brome and red fescue. The study found that although the sod was more expensive to use than the seed mixture traditionally used in bioswales by Caltrans, the native grass sod made up for the extra expense with its superior resistance to weeds and sediment retention.

Grass and Sedge Mixture

• A 2008 project conducted by landscape architect Marcus de la Fleur in Elmhurst, Illinois, attempted to develop sustainable, environmentally friendly methods for controlling and utilizing rainwater runoff. A bioswale was constructed on the project's residential lot, and it was planted with a mixture of native prairie grasses and sedges rather than the typical turf grasses. Straight-styled wood sedge, silk wild rye, bottlebrush grass and spike grass were planted, along with a number of non-grass native species. The goal of using prairie grass was to slow water flow through the swale more than turf grass would, thereby reducing the volume of runoff, increasing the precipitation of contaminants out of rainwater and allowing more of the runoff to filter into the ground water.

Other Plant Options

• Non-grass plant species, or forbs, can also be used in bioswale planting mixtures. Aster, wild geranium, coneflower and Rudbeckia are all appropriate complements to grasses and sedges, and ornamental perennials, shrubs and trees may be added to the landscaping to improve the aesthetic appeal of the swale.