Residential rain gardens are a natural way to manage the rain on your property while adding beauty to your landscape. They can be a good solution for flatter spaces where the soils allow water to quickly and safely soak into the ground.
City of Portland, Oregon
What Is a Rain Garden?
A rain garden is a shallow bowl-shaped dip in the landscape that collects rainwater. They are often planted with native plants and can be designed with a formal or informal aesthetic. A rain garden is a great place to direct rain runoff from roofs or paved areas, as well as the overflow from another rainwater collection system such as a rain barrel. They can even be used to help manage or drain a naturally wet area in your yard. Rain gardens add beauty to your landscape while managing the rain and providing habitat for birds, bees, and other pollinators.
How Rain Gardens Work
In general, rain from a roof or paved area is directed to the rain garden where it is collected and stored until it can safely soak into the ground. The rain garden’s plants and soil filter out chemicals, dirt, and other pollutants picked up by the rainwater as it washes over hard surfaces. This keeps rainwater out of the sewer system, helps reduce the risk of sewer backups or overflows to the Willamette River, protects our rivers and streams from pollution, and replenishes groundwater.
Summary of Rain Garden Design Requirements
These site and design requirements can help you decide if a rain garden might be appropriate for your project.
Rain gardens are not very deep, so they can be created without professional help if you pay attention to important safety measures.
To stay safe and avoid damaging buildings or other structures:
The edge of the garden must be:
At least 6 feet away from a building with a basement or 2 feet from a building without a basement.
At least 5 feet away from neighboring properties.
At least 5 feet from the base and 10 feet from the top of retaining walls higher than 3 feet.
The deepest part of the rain garden should be at least 10 feet from any neighboring structures.
When building a rain garden, it’s also important to keep in mind:
The infiltration rates of the soils (how well water soaks into the ground). An infiltration test is recommended prior to rain garden construction. Find information on how to do an infiltration test in the How to Build a Residential Rain Garden guide below on this page.
The minimum suggested ponding depth of the finished rain garden should be 6 to 12 inches. Rain gardens should completely drain within 24 hours of a rain event.
Be cautious of underground utilities. Do not build over water, gas lines or oil tanks. Call before you dig, 1-800-332-2344, 8-1-1, or schedule an appointment online to locate all underground utilities.
Rain gardens are not suitable for steep locations — property with more than a 10 percent slope.
Avoid compacting the native soils. The rain garden must be large enough to handle the runoff directed to it. Sizing will depend on tested infiltration rates and catchment area.
Every garden should have a safe escape route. Plan where the rain will go when the garden is full and direct it away from structures and neighboring properties.
When choosing plants for your rain garden:
Install plants from the Stormwater Management Manual plant list or choose plants appropriate for the native plant community type as described in the Portland Plant List.
Environmental Services prohibits plants on the Portland Nuisance Plant List and the Required Eradication List. Both categories can be found in the Portland Plant List. Find a link in the Resources section below.
Find More Resources
How to Build a Residential Rain Garden. This printable how-to guide from Environmental Services will walk you through the steps to plan, design, and build your rain garden.
Low-Impact Development Fact Sheet on Rain Gardens by Oregon State University Extension Service provides a detailed overview of all aspects of rain gardens from site conditions to maintenance. Get the Low Impact Development Fact Sheet
These site and design requirements can help you decide if a rain garden might be appropriate for your project.
Rain gardens are not very deep, so they can be created without professional help if you pay attention to important safety measures.
To stay safe and avoid damaging buildings or other structures:
The edge of the garden must be:
At least 6 feet away from a building with a basement or 2 feet from a building without a basement.
At least 5 feet away from neighboring properties.
At least 5 feet from the base and 10 feet from the top of retaining walls higher than 3 feet.
The deepest part of the rain garden should be at least 10 feet from any neighboring structures.
When building a rain garden, it’s also important to keep in mind:
The infiltration rates of the soils (how well water soaks into the ground). An infiltration test is recommended prior to rain garden construction. Find information on how to do an infiltration test in the How to Build a Residential Rain Garden guide below on this page.
The minimum suggested ponding depth of the finished rain garden should be 6 to 12 inches. Rain gardens should completely drain within 24 hours of a rain event.
Be cautious of underground utilities. Do not build over water, gas lines or oil tanks. Call before you dig, 1-800-332-2344, 8-1-1, or schedule an appointment online to locate all underground utilities.
Rain gardens are not suitable for steep locations — property with more than a 10 percent slope.
Avoid compacting the native soils. The rain garden must be large enough to handle the runoff directed to it. Sizing will depend on tested infiltration rates and catchment area.
Every garden should have a safe escape route. Plan where the rain will go when the garden is full and direct it away from structures and neighboring properties.
When choosing plants for your rain garden:
Install plants from the Stormwater Management Manual plant list or choose plants appropriate for the native plant community type as described in the Portland Plant List.
Environmental Services prohibits plants on the Portland Nuisance Plant List and the Required Eradication List. Both categories can be found in the Portland Plant List. Find a link in the Resources section below.
When to Call a Professional
A professional designer is not required to design and build most home rain gardens. However, if you want help in selecting your plant palette, a nursery professional can help you pick out suitable plants based on your soil, sunlight, and garden design.
Costs and Permits
Rain gardens are not approved for any new construction or redevelopment project that activates the Stormwater Management Manual requirements. See the manual for more information.
The cost of installing a rain garden depends on many factors such as size, plant selection and density, and other possible work such as removing paved surfaces or rerouting downspouts.
You will need a City permit if your project involves any of the following activities or if any of the following conditions apply to your property.
You excavate or remove more than 10 cubic yards of dirt (that’s about enough to fill one standard size dump truck).
Your property has a 10 percent slope or more.
Your property is within 50 feet of a wetland or waterbody. Your property is in a floodplain.
You do not need city permits to construct a residential rain garden if:
If any of these conditions apply to your property, you may need to take extra steps to safely install a rain garden. Contact the Private Property Drainage Inquiries team to discuss safe options for your property.
Maintenance Requirements
Like any garden, a rain garden requires some regular maintenance. Once the garden becomes established, which happens in about two years, maintenance should be minimal. Because they collect lots of water, it is important to inspect your rain garden periodically, especially after a heavy rain.
Other ongoing maintenance tasks include:
Water the plants deeply once a week during dry months (May to October) to encourage root growth and keep plants strong, especially while plants are getting established during the first two summers.
Pull weeds by hand before they become established (avoid chemical weed killers).
Remove sediment and debris, watch for erosion, and replace plants as needed.
Regularly check gutters, downspouts and inlet pipes to ensure they are free and clear of debris and that rainwater can enter the garden.
Once a year, layer compost or mulch 2 inches deep to suppress weeds and feed plants.
Thin and prune plants as needed. Divide dense plantings every two to five years.
Remove leaves in the fall. Leaf build-up will reduce rain garden capacity and smother plantings.
Stormwater Management Manual
Consult the City’s Stormwater Management Manual for the complete set of requirements on how to safely site, build, and maintain a rain garden or other stormwater management solution on your property.
Clean River Rewards Eligibility
Residential and commercial property owners who install qualified stormwater management solutions may be eligible for a discount on the stormwater charges of their sewer, stormwater, and water bill through the Clean River Rewards program.
Rain gardens that meet the safety and space requirements outlined above and are at least 10 percent of the area of the roof that is draining to it are eligible for Clean River Rewards. Visit Clean River Rewards to learn more.
A rain garden is a bowl-shaped depression designed as a garden to capture, hold, and absorb rainwater. Rain gardens slow the flow of rainwater from roofs, sidewalks, streets, parking lots, and other impervious surfaces, allowing the water to penetrate the soil.
The soil cleans the water of pollutants before it enters the storm drain and empties into our bayous and bays. This process allows us to keep more of the rain that falls on our yards, and the storm water that finally enters the storm drain is cleaner.Rain gardens use native plants as well as nonnative plants that are adapted to our climate. When designed properly, water in the rain garden should stand for no more than 24 to 48 hours, too short a period for mosquitoes to hatch.
Another benefit is that rain gardens serve as habitats for wildlife such as birds and butterflies. They are useful for residential, commercial, and public areas.
Above all, a rain garden is a landscape amenity, blending beauty and function—an attractive WaterSmart solution to water pollution.
Proposed to be constructed in the southern portion of the AgriLife Campus the rain garden will have curb openings with a concrete flume that will allow for runoff to drain to a collection point within the garden for automatic sampling and flow measurement. A surface overflow box will drain water to an underground pipe away from the median. Additionally, the drainage layer of the rain garden will house perforated pipes that will assist in soil infiltration. A flow measurement device will measure the overflow and perforated pipe. Water quality samples will be collected with an automatic sampler. A pressure transducer will be installed within a well point to measure soil water storage. The outflow will drain into a depression/ ditch via a flume. Plants will be selected based on optimal performance of the rain garden, including treatment of the storm water. Overall, the monitoring data will be used to quantify total water inflow (runoff), outflow (runoff and infiltration), soil water storage, and pollutant balances. The rain garden will also be maintained beyond the scope of this project as a demonstration for the public.
What is rain garden? A rain garden is a beautiful and effective way to clean polluted stormwater runoff. A rain garden acts like a miniature native forest by collecting, absorbing, and filtering stormwater runoff from roof tops, driveways, patios, and other areas that don’t allow water to soak in. They can be built at several scales and one may be just right for your home or neighborhood. Rain Gardens are simply shallow depressions that: # Can be shaped and sized to fit your yard. # Use a special mix of sand and compost that allow water to soak in rapidly and supports healthy plant growth. #Can be landscaped with a variety of plants to fit the surroundings.
Will it be expensive or difficult to install and maintain a rain garden? Once a shallow depression is dug for the rain garden, it won’t be any more expensive than planting other landscaped areas in your yard. Most of the recommended plants can be purchased at local nurseries and you maintain them just like any other plants in your yard. If you are using native plants, once established, they will require less water and no fertilization.
Won’t a rain garden create a pond for mosquitoes? No, a rain garden is not a pond. When properly constructed, the water will drain within 48 hours (but usually faster). Mosquitoes won’t find rain gardens to be good breeding areas because they need much more time to lay and hatch eggs.
I’m interested in building a rain garden. What should I do next? Visit http://www.cmhc.ca (or any equivalent website in your area) and type “rain gardens” in the search field for more information on rain gardens. *Note: This information is provided for your benefit only. If you do not feel comfortable in constructing your rain garden, please consult a landscaper. The City of Calgary will not be liable nor responsible for any bodily or personal injury or property damage of any nature that may be suffered from the construction of your rain garden.
What’s are Benefits of Rain Gardens Low maintenance. Rain gardens need no more care than regular landscaping. Grows quickly. Extra moisture and loose, deep soil make plants thrive and quickly fill in a space. Provides habitat. Rain gardens can provide abundant food, water, and shelter for wildlife such as birds and butterflies. Diversifies plant possibilities. Extra natural moisture means you can have a water-wise garden while including more moisture-loving plants you might otherwise have had to leave out. Improves aesthetics. Rain gardens add visual interest to your yard and your community.
Why Rain Gardens are Best for… Properties with more space. Rain gardens are simplest to install when you can stay at least three metres away from building foundations. Newer properties with mostly manicured turf. Typical groomed turf is usually underlain with a shallow soil that is inhospitable to plant survival, doesn’t break down contaminants, and creates a lot of runoff. Adding rain gardens to this type of property (newer than about 1970) will instantly improve its performance. Areas where a tree canopy is yet to establish. If you have mature trees, your property is working hard already, and rain gardens are a type of feature that might be difficult to fit in. Where you don’t have trees, rain gardens are a major performance booster.
Rain Garden Basics
What is a rain garden? A rain garden is a beautiful and effective way to clean polluted stormwater runoff. A rain garden acts like a miniature native forest by collecting, absorbing, and filtering stormwater runoff from roof tops, driveways, patios, and other areas that don’t allow water to soak in. They can be built at several scales and one may be just right for your home or neighborhood.
Rain Gardens are simply shallow depressions that:
Can be shaped and sized to fit your yard.
Use a special mix of sand and compost that allow water to soak in rapidly and supports healthy plant growth.
Can be landscaped with a variety of plants to fit the surroundings.
Why do we need raingardens? Stormwater is nothing but rainfall after it falls on the earth’s surface and travels across the landscape to a nearby stream or other water body. In landscapes that have been altered by humans, this stormwater picks up everything we humans leave behind – things like oil and gas, heavy metals, fertilizers, and animal waste.
Scientists have confirmed that stormwater is harmful to humans, animals, and fish that come in contact with it. Eventually stormwater makes its way to Puget Sound impairing the Sound’s water quality, impacting our shellfish and fisheries industry, and limiting recreational opportunities. (Source: https://extension.wsu.edu/raingarden/featured-rain-gardens/)
WSU research and experiments have shown that stormwater collected from highways around Puget Sound is lethal to fish. However, when that same stormwater was filtered through a special rain garden soil mix – the fish lived. Rain gardens can be a important tool in limiting the amount of contaminated water reaching our streams and Puget Sound.
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