Rain Gardens

Photo from: http://commons.wikimedia.org/wiki/File:Bioretention_cell_rain_garden_US_winter.jpg

We took a field trip to the landscape arboretum a couple weeks ago, which got me thinking about rain gardens.  I thought I would share a short how-to on rain garden design, and talk about why they are so wonderful.

Rain gardens use deep-rooted plants in a slightly depressed area to capture rain water runoff before it goes into storm drains.  When water flows off of a lawn, it contains all sorts of nasty stuff--lawn chemicals, salt, oil, sediment, etc.  When this contaminated water flows directly off of our yards and into the storm drain, it ends up in our lakes and rivers. Rain gardens are able to capture this water, and the plants, mulch, and soil essentially filter out the pollutants.  Plants in the garden use the water, putting fresh clean water back into the cycle. It's a beautiful thing. So how do you go about designing and building such an awesome garden?

First things first- select your site. The garden should be at least 10 feet from your foundation, and should be built in a location where water naturally flows (i.e. at the bottom of a small slope). Underground drainage systems can be installed to direct the flow of water, but that's beyond my knowledge. Before digging, of course call 811 to have the city mark your gas and electric lines of course.

Have your soil checked out to make sure that drainage will happen properly. The University of Minnesota does affordable soil tests. If the soil is too clayey or too sandy, it can be amended with compost.  Sand or sandy loam is preferable for rain gardens. 

Now that you have all that out of the way, it's time to start digging. Ideally the garden should be dug out about six inches.  This can be a trench or just a flat area.

Then comes the fun part--planting! Native plants are ideal for the rain garden, as they generally have good, deep roots and will create beneficial insect habitat.  They also usually require less inputs, like fertilizers.  Trees, shrubs, wildflowers, and grasses can all have a place in a rain garden, depending on the size.  Check out the Minnesota DNR website for more information on native MN plants.
Minnesota Native Plants: DNR

Lastly, add a few inches of mulch. Woodchips work well. This will help plants get established, suppress weeds, and prevent soil erosion.  Water plants regularly while they get established. Maintenance is pretty simple in the garden. Regular weeding and mulching are basically the only things you should need to do.  Once the plants are well established, their deep roots should be very drought tolerant.