The Rain Garden

Filed in Gardening by on February 3, 2015

ruducerunofforg

By Reba Gilliand | Photo Source: reducerunoff.org

 

Rain gardens not only enhance the beauty of homes and neighborhoods, they help protect one of our most valuable resources – water.

 

The idea behind the rain garden is that it creates a way for rainwater to soak gently into the ground rather than run torrentially over land into storm sewers or directly into waterways, making gullies and dragging soil and pollutants along the way. Neighborhoods, communities, and whole watersheds benefit because rain gardens help limit the amount of nutrients and sediments carried into lakes, rivers, and wetlands. Lakeshore and other waterfront property owners directly benefit as rain gardens help improve water quality on their lake or waterway as well as prevent erosion and provide wildlife habitat.

 

Simply put, a rain garden is a shallow depression designed to catch rainwater, filled with plants that don’t mind damp feet.

 

To be functional as well as beautiful, a rain garden must be planned and its installation well executed. Planning considerations include location, size, and design, while execution includes site preparation, plant choice, and planting the rain garden.

 

With basic knowledge and some “sweat equity,” rain gardens can be a great do-it-yourself project. Many guides are available to help the do-it-yourselfer create a rain garden that’s both beautiful and functional. The Blue Thumb Guide to Raingardens (2007) by Schmidt, Shaw and Dods published by Waterdrop Innovations is a good source. The University of Wisconsin Extension offers a downloadable “how to” manual at http://learningstore.uwex.edu/pdf/GWQ037.pdf.

 

An overview of the steps involved may help decide whether to tackle building a rain garden yourself or hire a professional.

 

Locate it optimally

 

Rain gardens need to be located where they can slow and catch rainwater. Such locations include places where water drains away from downspouts, sump pump outlets, or driveways, or where storm water runoff flows in paths through the yard. Avoid positioning a rain garden over buried utility lines, on top of septic tank leach fields, over water-supply wells, beneath trees, over shallow bedrock, in a wetland, as well as draining into your basement, or into your neighbor’s yard. To catch downspout runoff, position the rain garden at least ten feet from your basement, (twenty if you have room). To catch downhill runoff such as from a driveway, position it on the slope rather than the lowest spot. In positioning the rain garden, consider your overall landscape design as well as water flow.

 

Size the rain garden properly

 

Rain gardens are typically from four to eight inches deep and cover an area that fits the space you have available and the amount of water you want to capture. Depth is determined by infiltration rate, which depends upon soil type—sand, clay, loam, etc. The proper depth is one that allows collected water to seep into the soil within 24 hours. A percolation test determines the rate water infiltrates your soil. The size of the area covered by the rain garden is less critical than the depth. A rule of thumb is to size the garden so it holds about an inch of the rain that falls on the area draining to the rain garden. Still, the most important consideration when sizing the garden is how it fits into your landscape design.

 

Design the rain garden for water flow and beauty

 

Plan the path runoff will travel to reach the rain garden. Shape the rain garden so it is pleasing aesthetically. Try different shapes with a garden hose or rope until you find one that suits you. If you have the space available and a somewhat steep slope, you might consider two or three depressions laid out in stair-step fashion instead of one.

 

Prepare the site

 

Once you have decided upon a shape, remove the sod and start digging. Your goal is to create a wide flat-bottomed depression with gently sloping sides to the depth determined by the infiltration test. If situated on a slope, you’ll need to berm the downhill side to contain the runoff. Whatever the characteristics of your property, the rain garden will need an inlet and outlet. Prepare the soil – After the garden is shaped, sized, and designed to capture water flow, prepare the soil for planting. Like any garden, preparation depends on the soil you already have. Have a soil test run to determine whether your soil needs amending. Whether adding amendments or not, till the garden bed to loosen the subsoil, add additional soil to the correct depth, and rake and grade to the shape you want.

 

Create a plant “blue print” and choose plants

 

Draw a design on paper before purchasing plants so you’ll know the number of each type of plant to fill your rain garden and the spacing required for each plant.

 

Select plants that are well suited for the conditions in your landscape/rain garden. Plants vary in their moisture tolerance, sun preference, size, aggressiveness, seasonal interest, salt tolerance, and attractiveness to birds and butterflies.

 

Hundreds of plants are suitable for planting in a rain garden, both Midwest natives and non- natives. Natives, such as purple aster, red-osier dogwood, or prairie smoke, are a good choice because they tend to be more tolerant of soil conditions, need less maintenance, and have deep roots to filter pollutants. Non-natives will work too as long as the plants you choose meet necessary moisture and sun conditions.

 

To simplify plant selection, rain garden how-to books and online resources contain sample designs or “blue prints” for rain gardens of various square footages, shapes, conditions, and effect, including the names and numbers of plants needed to create the design. For example, the University of Wisconsin Extension how-to manual contains, among others, a blue-print for a “10 foot wide rain garden in full to partial shade with silty and sandy soils.” For those wishing to create their own plant design, guides such as Blue Thumb contain lists of plant choices appropriate for rain gardens.

 

Plant and add mulch

 

Once you have plants, set them into the garden where they’ll go, make any adjustments and plant them, working in sections from the center outward. Add a three-inch thick layer of coarse, double-shredded hardwood mulch around plants and an edging to keep grass from growing into the rain garden.

 

Like most gardening projects, a rain garden takes some planning and effort, but the outcome is well worth the time that goes into creating it. Whether you do-it-yourself or have someone do it for you, you will add value and beauty to your landscape with a rain garden AND help protect our water.

 

 

 

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