Rain Gardens

What is a rain garden?

A rain garden is a planted depression in the landscape that is designed to collect, absorb and filter stormwater. Rain is intercepted at a chosen point (such as a driveway or roof downspouts) and directed to the planted depression. As the water percolates through the soil, the natural filtering abilities of soil micro-organisms and plants clean the water. A rain garden is planted with appropriate plants, making it an attractive addition to the landscape. It is constructed using soil mixes that allow water to soak in rapidly and support healthy plant growth.

By planting a rain garden, you can help keep protect local streams, lakes and groundwater. As our cities and suburbs have developed, the amount of pavement has increased dramatically. Hard surfaces such as roads, driveways, patios and roofs don't allow rain water to soak into the soil. Instead, the water runs off into streams and lakes, causing flooding, scouring stream banks and carrying pollutants such as pesticides, fertilizers and motor oil.

Scientists working to restore Puget Sound name stormwater as one of the major contributors to the decline of the Sound. According to the US Environmental Protection Agency, stormwater runoff is the leading threat to the nation's estuaries and the third-largest problem facing lakes.

Things to think about when considering a rain garden

Where to site the rain garden. Rain gardens should be kept a minimum of 10 feet from any building foundation. They are not appropriate over septic drain fields or shallow utilities.

Soil type. Not all soils will be suitable for a rain garden. Fast-draining soils are best. A simple soil particle test can help determine how quickly your soil will drain . Amending or replacing the soil may improve drainage rates. Soil type and drainage will also be a factor in determining rain garden size. (See below)

What are your collection points? You could use a roof, driveway, neighbor's lawn, etc. This will help determine the actual size of your rain garden.

Sizing. How big will the rain garden need to be? How much area is draining to the rain garden? How much space is available? How much water from the drainage area will the rain garden hold? How quickly does water drain from the area?

The following references will provide more detail on benefits and construction of a rain garden. Or call In Harmony to assist you with your design at 425-486-2180.

References & resources

Rain garden handbook for western Washington homeowners, www.pierce.wsu.edu/Water_Quality/LID

How to build a residential rain garden, http://www.portlandonline.com/shared/cfm/image.cfm?id=188636

Rain garden tips, http://www.sueellingson.com/raingardens/ or www.raingardens.org/