Whether you realize it or not, you have probably seen a rain garden before. The lush greenery they provide often catches the eye. But beyond their beauty, rain gardens serve a larger purpose by utilizing the power of nature to effectively manage stormwater.
What is a rain garden?
Rain Gardens are shallow, planted depressions that collect, absorb and filter rainwater runoff from impervious surfaces.
Rain gardens, also sometimes called bioretention areas, are a beautiful and accessible form of green stormwater infrastructure. They are shallow depressed areas of soil that are planted with native grasses, shrubs, flowering perennials, or a combination of native plants. Below the plants, rain gardens have layers of soil, sand, gravel or a combination of these materials.
How do rain gardens work?
When rain falls on impervious surfaces, such as roofs, sidewalks and parking lots, it then flows downhill, collecting sediment, pollutants and more as it goes. Typically, this water then goes into storm drains or otherwise makes its way back into the environment.
Rain gardens intercept this process by collecting rainwater before it returns to the environment. By collecting stormwater in a recessed area, rain gardens slow the water and allow it ample time to soak into the soil. As the water infiltrates, it is filtered by the soil, sand or gravel.
Some of the water is absorbed by plants, which also remove excess nutrients and maintain the soil porosity necessary for efficient water absorption. The rest of the water infiltrates deeper into the soil, where it continues to be filtered along with the help of soil microbes.
A freshly planted bioretention area. Photo curtesy of Fouad Jaber.
A bioretention area at the Texas A&M AgriLife Dallas Center.
What are the benefits of rain gardens?
Improved water quality: A primary benefit of rain gardens is improved water quality. By slowing down water, rain gardens provide time for pollutants to settle out. Then, during infiltration, the soil, sand or gravel filters the water and improves water quality.
Plants also play a role in improving water quality, since they take up excess nutrients that may have entered the water from fertilizer and animal waste runoff. Additionally, microbes in the soil can turn pollutants like hydrocarbons into gas. This process, known as volatization, can render the pollutants harmless.
Reduce stormwater runoff: Rain gardens also benefit communities by reducing stormwater runoff. Typically, the amount of water that infiltrates soil is dictated by the soil’s water-holding capacity. Water that cannot be absorbed continues downhill until it finds soil that can absorb it, reaches a body of water, or evaporates.
With rain gardens, infiltration is increased because water is forced to remain in one location until the soil can absorb it or it evaporates. Typically, the materials in rain gardens are designed to optimize the garden’s water-holding capacity. This reduction in stormwater runoff also leads to reduced intensity and frequency of flash floods. Additionally, the slowing of runoff reduces erosion to stream beds.
Why do rain gardens use native plants?
- They do not require fertilizer.
- They have good root systems.
- They are better at utilizing available water and nutrients than non-native plants.
- They provide habitat for native species.
Other benefits: Rain gardens are an inexpensive option for stormwater management and require minimal maintenance. These traits, along with their beautiful greenery, make rain gardens the perfect addition to front lawns, backyards, and gardens. Rain gardens also include native vegetation that provides habitats for pollinators, birds, and wildlife.
A rain garden.