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Rain Gardens / Bioretention / Bioswales

A rain garden is a functional landscaping technique that can beautify your property as well as help filter and slow the flow of stormwater.

Image of a rain garden

Rain gardens are saucer shaped gardens that water flows into that are planted with grasses, flowers, shrubs, and sometimes small trees. They soak up water while providing wildlife habitat. The soils and basin fills with water for a short amount of time before soaking back into the surrounding soil. Plants used in these gardens are adapted to survive in short periods of flooding as well as dry soils in between storms.

Rain gardens often collect water from roof gutters, driveways, and sidewalks. Rain gardens are common around homes and townhomes. 

 

 

What is a Bioretention Garden? A Bioswale?  

Bioretention gardens are often used interchangeably with rain gardens.  They are almost the same thing, except one main difference - bioretention gardens have underneath drainage, while rain gardens depend on the soil for proper drainage.  Rain gardens are built with native soils mixed with compost or a special soil mix, while bioretention basins have special soil mix and gravel beneath the soil to hold more water. Furthermore, rain gardens do not have a buried perforated pipe.

bioswale is similar to a bioretention area in the way it is designed with layers of vegetation, soil and a perforated pipe within the bottom stone layer. Bioswales typically are located along a roadway and can be planted like gardens or covered in turfgrass.

 

Why Should I Install a Rain Garden?

Rain gardens allow about 30% more rainwater to soak into the  ground than traditional lawns. Since rain gardens capture  stormwater onsite, they can reduce the harmful effects to streams caused by large and rapid stormwater flows. 

Rain gardens offer multiple benefits to the community and the local environment, which include:

  • Reduced polluted stormwater runoff from yards into local streams

  • Reduced localized flooding

  • Reduced erosion

  • Pollution prevention

  • Groundwater recharge

  • Enhanced wildlife habitat

  • Aesthetics

However, the most important reason to install a rain garden may be that you are doing your part to help the environment and protect your local streams and the Chesapeake Bay. 

 

 

 

Resources

  • Low Impact Development Center - Rain Garden Design Templates
    This site was developed through an NFWF grant to display a series of rain garden, or bioretention, design templates that can be used by landscape architects, landscape contractors, and garden clubs throughout the Chesapeake Bay. These designs are intended to promote the use of rain gardens and Bayscapes by providing a set of easily accessible high quality sustainable and maintainable designs for the landscape industry and citizens. A demonstration rain garden was constructed at Brookside Gardens and showcases rain garden plants for sun and shade.
  • Using Rain Gardens to Reduce Runoff
    Slow it down, spread it out, soak it in!  Learn about rain gardens and other low impact development through the EPA webinar archives database. Three presentations detail rain garden basics.

 

Is a Rain Garden Right for Me?

Not all sites are suitable for a rain garden, and a conservation landscape may be a more appropriate project. If you have poorly drained soils, steep slopes, or space constraints, you should consider conservation landscaping

  • This is a good option if your property has sufficient space for the rain garden and overflow area

  • You need adequate space in your yard

  • You must have soils that drain well

  • They can vary in cost depending on the size and type of plants used and how much of the installation labor is done by the owner

  • They have maintenance requirements that vary depending on plant selection

 

Image of the front of the RainScapes Rain Garden Guide
Want Help with Assessing Your Property and Designing a Rain Garden?  Download the Guide. (PDF, 785KB)

How to Assess Your Property

Take some time to walk around your property to assess the drainage conditions. The best time to make your observations is when it is raining, so that you can see where the rain lands and where it flows. Consider these questions to help you identify where a rain garden could be placed to capture stormwater runoff on your property:

  • Are there places on your property where rain regularly runs off of a hard surface such as your roof, driveway, patio or compacted lawn?

  • Where does the rainwater go?  Is the runoff directed to your lawn, the street, or a storm drain?  Is my site right for a rain garden?

  • The rain garden should be placed so that it catches the runoff from your roof downspouts, driveway, patio, or sidewalk. The key is to place the rain garden between the point where rain falls on your property (i.e. your roof, driveway, or patio, etc.) and where runoff water would exit your property (i.e. an adjacent stream, storm drain, etc.). 

Once you have identified the pattern of drainage on your property, you can narrow down the potential rain garden locations on your property.  The RainScapes Rain Garden Guide has the completed steps for assessing your property on Page 3 as well as the ideas for designing and building your garden.

 

Image of people installing a rain garden.Installing Your Rain Garden

Ready to move ahead with installing a rain garden?  

There are a lot of decisions that need to be made with your rain garden after the assessment is complete.

  • Sizing the rain garden

  • Developing a planting plan

  • Plant selection

  • Determining how water will get to your garden

  • Determining where water will go when your garden is full

  • Whether you want to do the project yourself

The RainScapes Rain Garden Guide (below) has suggestions and useful information on how to best make the necessary decisions.  The RainScapes program has knowledgeable and helpful staff who can help you through the process as well as the RainScapes Rewards Rebates program with great financial incentives for installing the garden.  

 

Download the RainScapes Rain Garden Guide (PDF, 785KB)

 
 

Maintaining Rain Gardens and Bioretention Basins

Image of the front of the Rain Garden Maintenance Fact Sheet.
Want Help with Maintenance, Troubleshooting and Timelines?  
Download the Fact Sheet (PDF, 255KB)
Rain gardens require maintenance to keep them healthy, functional and to prevent problems, such as mosquitoes and flooding.  Rain gardens, bioretentions and bioswales need regular maintenance similar to other landscaped areas including, weeding, removing trash and debris, pruning and mulching. You can prolong the life of your rain garden and save on maintenance costs by keeping your site clean and regularly inspecting and maintaining the garden to ensure it is functioning properly. Unmaintained rain gardens, bioswales, and micro-bioretention facilities may:
  • Stop filtering the rainwater and allow trash and pollutants to enter our local streams

  • Be difficult or expensive to restore if left unmaintained

  • Allow water to pool on the surface long enough to allow insects to breed (longer than 3 days)

By maintaining your practice, you are doing your part to help the environment and protect  your local streams and the Chesapeake Bay.  

 

 

Actions You Can Take to Maintain Your Rain Garden

Monthly Actions

As Needed Actions

✔ Regularly inspect the garden for signs of erosion, obstructions, or unhealthy vegetation.

✔ Cut back dead stems of herbaceous plants in March and remove from the facility.

✔ Remove weeds and invasive plants.

✔ Water new plants during initial establishment of plant growth (first 18 months) and extreme droughts. Watering should only be needed when it has not rained for more than 10 days. 

✔ Remove any trash that has washed into the bioretention area or the inlet channels or pipes.

✔ Replenish and redistribute mulch to a total depth of 3 inches.

✔ Check the facility a few days after a rain storm to make sure that there is not standing water after 2 days.

✔ Contact DEP if you observe severe erosion.

✔ Clear sediment and deposits from inlets.

✔ In Fall, remove fallen leaves from the area. Leaves may block the flow of rainwater.




Actions To Avoid to Maintain Your Rain Garden

Don't

✘ Don’t apply excess salt and sand around the property in winter.

✘ Don’t store snow and leaves on top of the garden.

✘ Don’t use fertilizer or pesticide.

✘ Don't direct sump pump water into the garden.

 

DEP can answer your questions and provide additional guidance about maintaining your garden. Please email askdep@montgomerycountymd.gov or call the Montgomery County Customer Service Center at 3-1-1.

 

Help Maintain Right-of-Way Rain Gardens and Green Streets

Do you have a rain garden or other stormwater management facility in the right-of-ways of your neighborhood?  You can help DEP by performing regular maintenance activities. 

 

Maintaining Right-of-Way Rain Gardens and Green Streets
Actions You Can Take Actions You Can't Take

✔ Mow outer edges.

✘ Don’t use fertilizer or pesticide.
✔ Water if it hasn't rained in 10 days and is within the first 18 month of planting, or, during extreme drought.

✘ Don’t plant or remove plants.

✔ Remove any trash that has washed into the bioretention area or the inlet channels or pipes. ✘ Don't mow the inside of the rain garden.
✔ Check the facility a few days after a rain storm to make sure that there is not standing water after 2 days. ✘ Don't prune or cut back plants.
✔ Regularly inspect the practice for signs of erosion, obstructions, or unhealthy vegetation.  Contact DEP if you notice problems.  

 

Want to learn more about maintaining Right-of-Way Rain Gardens and Green Streets? Email askdep@montgomerycountymd.gov

 

Rain Gardens in the Stormwater Facilities Maintenance Program

The Stormwater Facilities Maintenance Program is responsible for maintaining all public stormwater facilities as well as all private facilities that transfered their maintenance to the County.  The program also maintains facilities that were required as part of the Department of Planning permits.

Not sure if your rain garden is part of the Stormwater Facilities Maintenance Program.  Check out online Facilities Map or email askdep@montgomerycountymd.gov

Can I remove my rain garden after installation?

No, you cannot remove any facilities that were part of your building installation - these are permitted structures and DEP maintains a database of these facility locations as part of the Stormwater Facility Maintenance Program. DEP may perform a maintenance inspection of your practice if it is a permitted structure.  Property owners must contact DEP before any major changes can be performed to the structure. 

 

Rebates, Resources and Financial Incentives

Interested in installing a rain garden?  The County offers incentives to help make the decision a little easier.

 

Logo of the RainScapes programThe RainScapes Rewards Rebates Program

The County offers technical and financial assistance (in the form of rebates) to encourage property owners to implement RainScapes techniques on their property, including rain gardens. 

  • Residential properties are eligible for up to a $2,500 rebate

  • Commercial, multi-family or institutional properties are eligible for up to a $10,000 rebates.

To participate, your property must be located in Montgomery County, outside of the municipal limits of the City of Rockville, City of Takoma Park, or City of Gaithersburg. Projects are not eligible if they are associated with permit approval requirements for new building construction, additions, or renovations. 

​The program is funded each fiscal year (The FY begins July 1 and ends June 30).  Annual funds for the programs are limited, so rebates will be awarded on a first-come-first-served basis.

The RainScapes program also provides technical assistance to help with the installation of your rain garden.  They have a wealth of information, expertise and want to help!

Learn more on the RainScape Rewards Rebates webpage. 

 

Image of a front yard with conservation landscaping and a rain garden.

 

The Water Quality Protection Charge Credit Program

After you have installed your rain garden, you are now eligible to receive a credit off your annual Water Quality Protection Charge (found on your yearly property tax bill).  The credit provides an incentive for maintaining your rain garden and other stormwater management practices.  

You must apply for the WQPC credit separately – the credit will not be provided to you automatically.

Residential property owners can receive up to 50% off their WQPC depending on the type and size of stormwater management practices on the property. 

Non-residential and multi-family properties can receive up to 50-60% off their WQPC depending on the type and size of the stormwater management practices on the property. 

Learn more on the WQPC Credit webpage.