Rain gardens bring function, beauty to your yard
As more natural landscape is replaced by concrete and parking lots, management of stormwater runoff and snow melt is becoming increasingly important to prevent pollution of lakes, rivers and wetlands.
Runoff management is particularly important for homeowners and businesses in urban areas and on shorelines, where water unable to penetrate the soil collects pollutants from impervious surfaces, like driveways, and drains directly into surface water, like lakes.
Pollution isn’t the only concern when it comes to runoff. Increasing amounts and increased speed of flow from large paved areas, such as parking lots, can create erosion issues. Hard surfaces also tend to heat the runoff, which, if allowed to enter bodies of water unchecked, can cause problems for aquatic life.
An increasingly popular — and aesthetically pleasing — way of managing water runoff is to plant rain gardens. Rain gardens are shallow depressions planted with grasses, shrubs, flowers and other flood-tolerant species. These gardens are designed to collect stormwater runoff and snow melt, naturally filtering the water and removing the pollutants before returning it to the groundwater below.
Beyond the multipurpose benefits of rain gardens, beautiful native wildflowers and shrubs can be selected specifically to attract birds and butterflies.
When planning a rain garden, there are a few considerations to make before beginning installation.
First, find an area of your yard that is suitable for placement of a rain garden. Typically, low-lying areas are best to take advantage of the natural flow of water downhill.
According to the University of Minnesota Extension, rain gardens should be placed 10 feet or more away from buildings to prevent water damage to foundations or basements. They should also be at least 35 feet from septic system drain fields and at least 50 feet from drinking water wells.
It’s always best to locate utility lines before beginning any digging project, so dial 811 for assistance in finding those lines in your yard.
After determining an appropriate site for your rain garden, the next step is to test the soil. The purpose of rain gardens is to absorb water, so the soil needs to be porous enough to soak up water within 48-72 hours.
To test this, Extension recommends digging a wide, 10-inch deep hole and filling it with water. If the water has not been absorbed in three days, you can either amend the soil by adding organic matter to increase its holding capacity, or choose another site where the soil may be better suited.
Shape and size
The shape of your rain garden is limited only by the space you’ve selected and imagination, but the size needed can be determined based upon the area of hard surfaces on your property. Typically, rain gardens will range from 100-300 square feet, but a good rule of thumb is the garden will handle water runoff from a hard surface three times its size.
If you have a large roof or are installing a rain garden on a commercial lot, you may need to consider planting more than one.
In a handout she uses to teach classes on the subject, Extension educator Jackie Froemming wrote that it’s important to plan for overflow in the case that stormwater runoff may exceed the capacity of your garden.
Plant selection is the next step to building your rain garden. Native plants are usually the best choice for use in rain gardens, and may be required depending upon local ordinances and whether you’re altering shoreline property.
Extension compiled a list of native plants to use in rain gardens. Plants such as bottlebrush sedge, blue flag iris and softstem bulrush are best suited for saturated areas, while upland areas call for plants such as the purple prairie clover, big bluestem and June grass.
Shrubs and small trees can be incorporated. Highbush cranberry and black chokeberry can tolerate most conditions, while snowberry and downy arrowwood prefer the driest areas. Berry shrubs and small trees tend to attract various bird species to your yard.
Plants suitable for attracting butterflies include wild bergamot, black-eyed Susan and prairie blazing star.
The whole list, along with information on preferred sunlight exposure, flower color and bloom time, can be viewed at http://www.extension.umn.edu/Garden/yard-garden/landscaping/best-plants-.... Check with local garden centers for even more localized suggestions or for plants that may attract specific species.
Ready to install
Once you’ve settled on location, size, shape and plant species, it’s a good idea to sketch a design before you actually begin digging and planting.
Now the fun part: If you’ve followed all the steps so far, you should be ready for installation of your rain garden.
If using amended soil, you’ll want to dig deep enough to add 1-3 feet of the soil for proper drainage. Froemming recommends adding 2-3 inches of finely shredded mulch next, ensuring it’s finely shredded so it won’t wash away from rain events.
She also said to leave 4-6 inches of ponding area with a flat bottom. If your rain garden is on a slope, you may need to install a berm at the low end to hold the water in place.
You should now be ready to add your chosen vegetation. Follow planting instructions on depth and spacing for each species, as they will most likely vary quite a bit.
You’ve finished your rain garden! Since native plants tend to be hardier species that will thrive in their natural habitat, rain gardens are relatively low maintenance. Still, Froemming recommends keeping an eye on how effective your rain garden appears to be, particularly the first year, and to ensure you are watering regularly until the plants have become established.
You should monitor for flooding and adjust overflow if necessary, correct any erosion problems, add mulch to any bare areas that emerge and remove weeds.
In subsequent years, it’s still important to monitor erosion and overflow, but by now, if you’ve maintained the garden properly, it should be in good shape. Remove dead or diseased plants and replace them with new, continue to re-apply mulch, and each spring, take care to remove sediment and debris from the first rain. Check the garden monthly for any additional debris buildup.
Rain gardens are a fantastic way to combine practical problem-solving with natural beauty and are a great conversation-starter. Sit back, relax and enjoy your garden, knowing you’re helping to save our precious water resources at the same time.
Chelsey Perkins can be reached at firstname.lastname@example.org. Follow her at facebook.com/PEJChelsey and on Twitter @PEJ_Chelsey.