-Rain Gardens

A rain garden is a depression, filled with shrubs and perennials that collect water runoff from a roof or paved surface allowing it to infiltrate into the soil.  The Schoolyard Habitat site has compacted clay soil which has low permeability.  It is recommended that when building a rain garden in clay soil, it is important to increase the rain garden area. Also, adding soil amendments such as compost, pumice or perlite onehalf to two feet below the ponding area will improve water retention. (Important, do not use mason or ball field sand.) Mix in three inches of compost on the surface.  Other soil amendments that improve soil permeability include humic acid granules or concentrate to spray on (Tri-C HUMATE PLUS Soil Conditioner + Gypsum “Feeds the Soil” or Humic Acid from Soil Food Web)

How to Build a Rain Garden (SIMPLE METHOD)

Selecting a Location

  • The most logical location for our rain garden is in an existing low spot on our site.
  • Place the garden where downspouts will drain into it, directing water with a shallow swale if necessary.
  • Place your rain garden at least 10 feet from a building to keep water from seeping into and damaging the foundation.

Building the rain garden

It’s simple! Just follow three easy steps:

  1. Start by digging a 4-8” depression with gradually sloping sides as large in circumference as you like. (A good rule of thumb is to size your garden at 30 percent of the area of the roof from which it will be collecting water.) A 4-8” depth will allow water to be captured, but will dry between rain events.
    If you prefer to hold water in your garden in drier times, dig a portion a little deeper, say 18” in depth.
  2. Plant natives recommended for our area.
  3. Add untreated, shredded hardwood mulch to a depth of 3” on all of the bare soil around the plants to prevent erosion while your natives are establishing.


While our natives are establishing their roots, we will need to water them about every other day. This should be done for the first two to three weeks, or until the plants show that they are growing and doing well. Only water the plants when the top 1″ of soil is completely dry.


How to Build a Rain Garden (Based on percolation test METHOD)

Water runoff is a major source of pollution to our nation’s waterways and run off and erosion contributes to the flooding which is expected to increase due to climate change.   This fairly simple process (it requires a little more thought than a regular garden, and you need to dig a 6 inch depression).

A really helpful guide to a Do-It-Yourself rain garden is this brochure published by the UConn Cooperative Extension System. The brochure recommends that to  placement of the rain garden is important – choose a location with good drainage that is fairly level that could catch water flowing from a gutter.  Determine if the soils are suitable at your rain garden site by doing a small percolation test – dig a hole about 6 inches deep and fill it with water, if there is still standing water 24 hours later, this location has inadequate drainage and your rain garden will  become a rain puddle.

The 44-page illustrated guide, “Oregon Rain Garden Guide: Landscaping for Clean Water and Healthy Streams“.

Below, PDF from University of Wisconsin info on rain gardens.


types of rain gardens

Explore these References and Resources
•• Bannerman, R. and E. Considine. 2003. Rain Gardens. Wisconsin Dept of
Natural Resources, USGS. University of Wisconsin Extension,

•• Bornstein, Carol, David Fross and Bart O’Brien. 2005. California Native Plants
for the Garden. Cachuma Press, Los Olivos, California.
•• Claytor, R. and T. Schueler. 1996. Design of Stormwater Filtering Systems. The Center for Watershed Protection,
Silver Spring, Maryland.

•• Hunt, W.F. and N. White. Designing Rain Gardens (Bio-Retention Areas). A&T State University Cooperative
Extension, North Carolina. http://www.bae.ncsu.edu/stormwater/PublicationFiles/DesigningRainGardens2001.pdf.

•• Lancaster, Brad. Rain Water Harvesting Principles for Dry Lands and Beyond, Volume I: Guiding Principles to
Welcome Rain into Your Life and Landscape. Rain Sources Press, Tucson, Arizona.

•• Prince George’s County Maryland, Department of Environmental Resources (PGCMDER). 2002. Bioretention
Manual. Prince George’s County, Maryland.

•• Sharff, Misty. 2004. Native Grasses and Graminoids: Tools for Protecting Water Quality. Storm Water Program,
CSUS Office of Water Programs, Sacramento. California.

•• University of Maine Cooperative Extension. Landscapes for Maine: Adding a RainGarden to Your Landscape,
Bulletin #2702. Orono, Maine. http://www.umext.maine.edu/onlinepubs/PDFpubs/2702.pdf.

••Waterfall, P. Harvesting Rainwater for Landscape Use. University of Arizona Cooperative Extension
For more information, contact Monique Myers, D.Env, Coastal Community Development Advisor for California Sea Grant and
U.C. Cooperative Extension, nicmyers@ucdavis.edu, 805-645-1482. Prepared by Valerie Borel, vtborel@ucdavis.edu.

Design of Stormwater Filtering Systems
Prepared by Richard A. Claytor and Thomas R. Schueler
The Center for Watershed Protection
8391 Main Street
Ellicott City, MD 21043
(410) 461-8323

These web-based resources provide information about rain gardens and bioswales.
Bioswales and Rain Gardens: Making Runoff a Resource
http://extension.oregonstate.edu/hoodriver/MG/documents/bioswalebrochure.pdfThis 2-page brochure created by the Oregon State University Extension Service
Master Gardener Program provides a short overview of both rain gardens and
bioswales along with easy instructions on how to build one.

How to Manage Stormwater: Rain Gardens
This 8-page pamphlet created by the City of Portland Environmental Services
provides easy instructions for analyzing, designing, and building a residential
rain garden.

Rain Gardens: A How To Manual for Homeowners
The 32-page pamphlet created by the Wisconsin Department of Natural
Resources and the U.S. Geological Survey provides detailed information about
how to size and site, build, plant, and maintain a residential rain garden.

According to its creators, the State of Oregon Department of Environmental
Quality, “this document is an attempt to compile the best available information
on the design and use of biofilters (bioswales, vegetated filter strips, and
constructed wetlands) so that those sites that may have an application of one or
the other of these vegetated filtering systems will have information to make the
best decision on the design, construction, implementation, and maintenance of
these Best Management Practices. It is not a design manual but a practical,
based on experience and knowledge of sites that implemented these BMPs,
useful information on what works and does not work when designing,
constructing, and operating them.”

Rain Garden Network
A website with useful information and resources connected with rain gardens.


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