What is a rain garden?
A rain garden is a landscaping feature that captures rainfall and helps soak it into the ground. Rain gardens can be used to capture runoff from roofs, driveways, or yards, helping you to better manage drainage or ponding issues while reducing dirty stormwater runoff flowing into local waterways.
What distinguishes a rain garden from other landscaping is its shallow bowl-like shape designed to temporarily pond and soak up stormwater. The shallow depression of a rain garden has a level bottom with amended soils (soil mixed with sand and/or compost) that increases infiltration. They are planted with mostly native flowers, grasses, and shrubs with deep root systems that can tolerate moist to wet soils.
Benefits of rain gardens
- Provides attractive & functional landscaping
- Adds wildlife & pollinator habitat to your yard
- Helps soak up stormwater that may be causing issues in your yard
- Reduces stormwater runoff and the transport of pollution to local rivers and lakes
Rain Garden Examples
Why build a rain garden?
Improve water quality & stormwater drainage issues
In a typical urban environment, rainfall flows off our roofs, driveways, and yards. Then, it enters the street and flows into storm drains. As the stormwater travels across our yards and streets, it can pick up pollutants like grass clippings, fertilizers, oils, trash, and other chemicals. Water that enters street storm drains does not get cleaned, meaning these pollutants end up in our local waterways and, eventually, the ocean. In addition to water pollution, large quantities of stormwater generated from our homes, parking lots, and other impervious surfaces leads to erosion in our own yards and accelerated streambank erosion in our local waterways. Rain gardens help stop this cycle by giving the excess runoff a place to go to be soaked into the ground.
In your own yard, rain gardens can be a way to incorporate landscaping that serves a function. Do you have erosion issues along your foundation stemming from downspouts? Do you have a low spot in your yard that collects water every time it rains? Maybe you want a pollinator garden or some new curb appeal in your front yard. Rain gardens present a great opportunity to address existing problems with landscaping in a beautiful and beneficial way.
Wildlife & pollinator benefits
Beyond water quality improvements and increased curb appeal, rain gardens can be part of the solution towards saving our pollinators and increasing local biodiversity. Rain gardens planted with native plants make your garden a “2-for-1 deal” when it comes to water quality improvements and pollinators. The same native plants that filter and soak in stormwater also provide food for local wildlife not found in your everyday non-native cultivars. Our neighborhoods and suburban areas provide one of the best opportunities to increase biodiversity in our city, and you can help be part of that solution by installing a rain garden planted with native Iowa plants.
Rain gardens help us restore nature in the city.
How rain gardens work
A rain garden is a special kind of landscaping that purposefully collects water, temporarily ponds that water, and helps soak it into the ground. When it rains, water directed to the rain garden will fill the ponding area. Within 12-24 hours, water stored in the garden will soak into the ground or be utilized by plants. In the four photos below, a newly established rain garden in the Easter Lake Watershed in Des Moines fills with rainwater. After a few hours, water in the rain garden is soaked into the ground.
A functional rain garden has these key components:
- Inlet: Whether you are directing water from downspouts or from a small parking lot into a rain garden, each garden will have an entry point to let water flow into it. Sometimes, this entry point may look like a tile trenched underground from your downspout, a curb cut in a parking lot, or another design.
- Ponding area: The shallow bowl-like area that collects and temporarily ponds water is referred to as the “ponding area.” The ponding area in a rain garden is sized based on the area of land that will be contributing water to the rain garden. Ponding areas typically have a depth of 6 inches, but can range from 6 inches to 12 inches in depth.
- Soil: To soak in stormwater, rain gardens must have good, sponge-like soils. Most rain gardens are built in locations that will require that an amended soil mixture (consisting of sand and topsoil) is installed in the base of the ponding area.
- Plants: To further help soak in and absorb stormwater, deep-rooted plants that can tolerate moist soil conditions are planted in the rain garden. Deep roots will help to further break up the soil over time, creating more pore spaces to soak in water. Iowa native plants provide many options for grasses, flowers, and even shrubs with deep roots that will also benefit wildlife, creating beautiful and functional rain gardens.
- Outlet: Rain gardens are designed to capture stormwater, but during large rains there may be more stormwater generated than the rain garden can store. For these larger rains, a rain garden will have an outlet to let excess water exit the rain garden in a stabilized way.
Where to locate a rain garden
Rain gardens can work in many locations to help manage stormwater runoff. In general, rain gardens should be in locations where water can easily flow to and that will be able to soak in water. For more information about rain gardens locations, refer to following resources:
- Avoid locations with public utilities
- Stay 10 feet away from building foundations
- Stay 10 feet or more downslope from basements
- Make sure water can easily flow to the garden
- Make sure you can make the bottom of the rain garden flat, even on a hill (can incorporate retaining walls)
- Rain gardens should not collect water from more than 11,000 square feet (about 1/4 acre of land)
Planting your rain garden
Iowa native plants provide many options for flowers, grasses, and shrubs for rain gardens that will help to soak up water while also providing wildlife benefits. For ideas and references, check out the links below or consider reaching out to a local native plant grower who can help you find the best plants for your rain garden.
Rain Garden Research
Rain gardens are used all over the United States to help better manage urban stormwater and to improve water quality. Learn about rain garden success stories by clicking the links!
Demonstration rain gardens in Burnsville, Minnesota reduce stormwater runoff by 90%.
- Project results – City of Burnsville, Minnesota
- Project report – City of Burnsville, Minnesota
- Project details – Barr Engineering, Minnesota
- Land & Water Feature Vol.48 No.5 – Burnsville Rain Gardens
Protecting Como Lake with Rain Gardens
Rain garden funding resources
Iowa Rain Garden Design & Installation Guide
Rain garden inspiration – see rain garden examples & find ideas
The Rain Campaign
ENABLING PEOPLE TO PROTECT WATER