Prevent Stormwater Runoff with a Fashionable Rain Garden

MANCHESTER, Conn. - With April showers imminent, you'll soon be reminded of how much stormwater leaves your property. Water rushing through gutters and down driveways will find its way to the street's sewer if you don't have a way to trap it.

Instead of letting stormwater wash away, create a rain garden to keep it on site.

Michael Dietz presented on Rain Garden Basics at
the CMGA Symposium on March 15. 

At the 2014 Connecticut Master Garden Association's Symposium, Michael Dietz, Ph.D, NEMO program director and water resources educator, explained how a rain garden can be installed. The benefits can be clearly seen in densely populated (and paved) cities.

"Older cities have a runoff problem," said Dietz. "The sewage and runoff from the house combine and overload the sewer treatment plants. If it's overloaded, it goes into the rivers."

The main problem with stormwater runoff is that it can collect pollutants along the way. These pollutants can find its way into lakes, streams, ponds and rivers.

This is where a rain garden comes in handy: it is designed to collect and infiltrate storm water runoff from a roof or driveway. This way on-site pollution will not leave your yard but will be treated on site. How? The top level of the soil has the ability to filter water and, for example, can absorb metals from older roofs. The bacteria in the soil can even break down small oil spots from a driveway, Dietz told his class.

The rain garden is simple in design. It is a depression in the landscape (about six inches deep) that is often planted with native plants and topped with a layer of finely shredded mulch. It should be located at least 10-15 feet away from the foundation of a house and at least 25 feet away from a well or septic system.

"Don't put a rain garden in a wet area of the yard," said Dietz. That means there is a high water table in that area. Dietz also recommended avoiding soils heavy in clay matter, but this area can be amended by increasing its size and adding compost.

A rain garden should not be confused with a pond. "Ponding [in the area] is OK, but it should be gone within three to four hours. You don't want to see water ponding for a day or two days after a storm," he said. (Read more here.)

Another challenge is working with compacted soil. "Compacted soil is the number one killer of a rain garden," he said. "If a house is constructed in the last five years, you will have compacted soil." This is caused by the heavy machinery that was used on-site to build the house. "Compacted subsoil is not good to grow in," he said. Dietz recommends replacing some of the compacted soil with a sand and compost mixture.

Sample of the sizing map as seen on
my iPhone. 

There's an App for That
The University of Connecticut has created a (very) helpful website to learn more about rain gardens. One of the most helpful pieces of information that I found on the website is the soil map. "It gives you a rough idea of what to expect at your house," Dietz said. On the page, enter your address to get an idea of what type of soil absorption your garden contains.  (For example, in my area, my whole neighborhood is characterized as "excessively drained" due to our proximity to the Connecticut River.)

Over on the Sizing Map, if you once again enter your street address, you can click on the satellite view of your house to calculate the amount of runoff that will enter your garden. Once you hit the calculate button, the site will tell you how wide your rain garden should be (remember to keep a depth of six inches for the ponding area and three more inches for the mulch when digging out the area).

What's even cooler is that there is a free app available for smartphones with all the same data found on the website. So you can even use the sizing map while standing out in your garden to measure how big your garden bed is. (Cool!)

To learn more about creating rain gardens, check out the Rain Gardens website created by the University of Connecticut Center for Land Use Education and Research's (CLEAR) NEMO Program.