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Creating a rain garden for the Chesapeake Bay watershed

Rain garden at Anne Arundel Community College, Arnold, Maryland
Rain garden at Anne Arundel Community College, Arnold, Maryland
Photo taken by Stephanie Siemek

What is a rain garden and how do you know when you should create one? Well, it is a small garden containing certain types of plants that can tolerate extreme wet conditions. They help slow down and collect stormwater from a hilly location before reaching an impermeable surface. Once rainwater falls to the ground it has the potential to collect pollutants, sediments, and other type of runoff sources. This is then all carried to the storm drain. From here, it is a straight shot to an aquatic ecosystem, such as a creek, river, bay, and lake. Nutrients and pollution from stormwater runoff is a growing problem; yet there are many things we can do to mitigate this issue, starting with our own property.

If you have a yard that contains a moderate slope, your yard may qualify for a rain garden. Before doing so, there are some things you have to consider.

  • First be sure the location where you would like to install the garden is at least 10 feet away from any dwelling foundation and at least 50 feet away from any wells.
  • Do not place near any septic drain fields, under a large tree, or slopes larger than 12%.
  • They should be a minimum of 2 feet from the water table.
  • Plant your garden in a spot that only gets partial to full sun.

Once a proper location is determined, you must then identify the type of soil. Sandy type soil does best with drainage. You should also do a percolation test (aka perc test) to ensure there is good filtration (AACounty.org). You perform this test in the middle of the location where you plan on putting your rain garden after a rainy day. If it hasn’t rained, just dig a hole, pour some water in it until the soil is fully saturated, and then fill the hole again to the top with water and see how long it takes for the water to drain. Water must be completely gone within a 24-hour period in order to demonstrate a good location for a rain garden. The minimum percolation rate is 0.25 inches per hour (Missouri Botanical Garden). After you have assessed the location look into any permits you may need. Anne Arundel County’s website contains information about what permits are needed depending on the property. They also have a flow chart you may easily follow.

Once you have found the proper location, you can then determine the shape of your garden, such as crescent or kidney shapes. Long rain gardens also work well if you have a large amount of runoff that you are trying to catch.

The next step is to determine drainage area, ponding depth, rain garden area, width and length, and the amount of soil needed. All this information on how to do this can be found in the “Rainscaping with Rain Gardens… Working with Nature to Transform Stormwater Runoff into Garden Oases” by the Chesapeake Ecology Center.

Next create a map of the location of your rain garden and start planning which native plants you would like to include and where they would be placed. Have fun with this, but make sure the plants you select can tolerate wet conditions and the amount of sunlight it will receive. A list of plants can also be found in the “Rainscaping with Rain Gardens…” guide.

Keep in mind once your rain garden has been installed, it may need to be maintained like any other garden. Watering it regularly may be required in the beginning in order to enable the plants to become established. Then, yearly weeding or mulching may be necessary along with replacing dead or thinned vegetation.

Rain gardens may sound like a lot of work, but with a group of people it can be fun, rewarding, and a beautiful addition to your community or yard. It helps filter stormwater runoff that would otherwise carry pollutants through your watershed. The hard work of planning and executing is definitely rewarded in the end.

Help and questions can also be directed to a local Watershed Steward. These are volunteers who went through an intense training through the Watershed Stewards Academy who can help you gain some ideas about how to manage stormwater runoff and guide you through the rain garden process. They can also recommend the best professionals in the area for whatever rainscaping project is best for your property.