Engineering Prairie Plantings
The City of Madison Stormwater Management system is comprised of 1,500+ acres of stormwater land, mostly in the form of ponds that retain water, and greenways that carry water. The primary goal for all stormwater land is to have them efficiently carry, store or infiltrate stormwater to prevent flooding. Another goal is to provide quality urban wildlife habitat and recreational space. Planting with native plants helps achieve all these goals.
Since 1995, as new stormwater systems have been constructed and old ones repaired, Engineering has planted these systems with native prairie vegetation. The grasslands that once covered this corner of southern Wisconsin were comprised of prairie species with exceptionally large and deep root systems. Larger root systems mean that each plant can use more water, and deeper roots mean that a given area can hold more water. The improved infiltration capacity of native prairie plants makes them an excellent choice for stormwater ponds and greenways.
Our native prairie species have the additional benefits of helping to control erosion and reduce nutrient runoff, being hardy and drought-resistant, a great source of wildlife and pollinator habitat and aesthetically pleasing.
Unlike traditional stormwater land that is often planted to turf and mowed frequently, Engineering manages prairie-vegetated stormwater land to encourage the proliferation of native plants. Management strategies include managed mowing: timing mows to control invasive species and favor native species; spot mows to control invasive plants and avoid native growth; manual control of invasive species by digging, cutting or pulling; spot herbicide treatments of invasive species; prescribed burns to control invasive species and favor native plants; collecting and sowing native seed; planting native plants.
Two measures of the health of prairie plantings on Engineering land are the diversity, that is the number of different species, of native plants, and the amount of area covered by invasive species. Typically, the more native plant species and the fewer invasive species present, the more beneficial the planting is to wildlife and the more stable and capable of taking up stormwater. Using these two measures, most stormwater land can be split into one of several vegetation management categories:
Ponds and greenways that have medium to high diversity prairie plantings may fall into the “managed meadow” category. In order to favor native plants and suppress invasive plant growth, these ponds and greenways may be mowed strategically, managed with manual weed removal, and/or burned.
These may range in quality from diverse prairie plantings that are managed at the level of conservation areas, to less diverse plantings that nevertheless foster a few native species that still provide habitat and may require additional management to increase diversity or maintain the current native diversity.
These may be ponds or greenways with low native plant diversity. They may never have been planted with native species, or the plantings may not have proliferated. This category also includes ponds and greenways that may require more regular mowing for other reasons, i.e. safety or health, recreational use, or access purposes. These areas are typically comprised of non-native grasses or common weeds. They may be mowed anywhere from one time a year to several times a month during the growing season.
Pollinator Plantings and Rain Gardens/Biobasins
These special stormwater areas are typically smaller areas that contain highly diverse native plantings. Pollinator plantings may be on upland or downslope areas and have been planted with an assortment of native plants that are especially beneficial to pollinators—wildflowers, milkweeds and native prairie grasses. Rain gardens or biobasins are diverse native plantings set in natural or man-made depressions designed to capture and infiltrate stormwater. Both types of plantings require a large amount of manual maintenance and as such, comprise the smallest category of stormwater land.