Rain gardens are a great landscape feature that helps slow, collect, infiltrate and filter storm water. They are the best solution to turn a “problem” wet area in your yard into a real benefit. Designed for a low-lying area that collects rainwater you’ll find there are many benefits to a rain garden like transforming a bare, wet area into a green, blooming habitat that provides food and shelter for birds, butterflies, and other wildlife.
Increased stormwater runoff is the real problem. Add soil erosion to that and the result is vulnerability to flooding. Rain gardens can prevent both, helping to conserve water and soil.
Consider the water cycle shown above and then add human development to the picture. Humans create stormwater runoff when natural areas are developed, replacing them with a sea of impervious surfaces fragmenting our green spaces. Within a developed residential area, pollutants such as fertilizers, herbicides, pet waste, and oil are washed from lawns, streets, and parking lots into local streams and drainage systems.
How Rain Gardens Help
While a single rain garden may seem inconsequential, it has great value. Rain gardens slow the water down allowing for it to be collected in the garden’s depression. Settling soil, silt and organic material that are washed by the water from higher ground are also captured and prevented from washing away. The captured water slowly filters back into the soil where it is needed most.
As the water soaks into the soil, the deeply rooted plants in your rain garden act as a filter, removing pollutants from the stormwater. Now your rain garden has become a beautifully designed space in your yard with stunning plants that captures and treats stormwater!
No need to worry that your rain garden will become a breeding area for mosquitoes. When designed correctly you should not have standing water that lasts longer than 72 hours. This is a much shorter time frame than the 7 required for most species of mosquitoes to develop and hatch from eggs laid in standing water.
Rain garden basics
Choose a site. Locate your garden in a low lying area of your landscape that tends to collect rain water and is at least 10 feet from your foundation. Choose a sunny or partially sunny spot. Also consider how it can be incorporated into your existing landscape replacing an area of traditional turf grass where the lawn slopes toward the street. An area that would catch roof run off or water from a down spout is perfect. If the rain garden is located on a slope, create a berm on the low side to retail water and soil.
Compared to a patch of lawn, a rain garden allows 30% more water to soak in the ground.
Test drainage. Test the location’s drainage before you create the bed. Dig a hole 8 to 12 inches deep and fill the hole with water. The water should soak in within 48 to 72 hours. Soils heavy in clay will drain much more slowly than soils heavier in loam, silt or sand. Amend sites heavy in clay with organic compost to improve the soil and help drainage. If the site doesn’t drain within 72 hours, choose another site.
Start digging. Rain gardens can be any size, but a typical residential rain garden ranges from 100 to 300 square feet. The depth of the garden can range between four and eight inches. Anything too deep might pond water too long and if too shallow, it will require greater surface area to effectively manage water.
Add plants. Choose a variety of native forbs and grasses, planting those with higher water tolerance in the middle of the garden. Include plants of varying heights and bloom times to maximize the garden’s depth, texture and color. Plant in groups of three to seven plants of a single species. Go for diversity. In natural areas, a diversity of plant types not only adds beauty, but also creates thick underground root network that keeps the entire plant community in balance.
The chart below includes plants for our area suitable for a rain garden. Planting zones are indicated as:
Margin: the high edge around the rain garden that is the driest zone
Median: the area between the margin and center
Center: the middle of the garden that is deeper and will stay wet longest
Help it flourish. Rain gardens can be maintained with little effort after plants are established. Weeding and some watering during dry periods will be needed the first two years.