Photo (Above): Rain garden at KY Horse Park.
Rain gardens are man-made landscape features that include a shallow (6 – 9 inches deep) depression designed to capture and reduce stormwater runoff. By installing a rain garden homeowners can intercept stormwater and keep it on their property. This allows stormwater to infiltrate into the soil rather than moving to a nearby ditch or stream. Rain gardens are particularly important in urban areas because developed land (pavement, buildings, and compacted soils) increases stormwater runoff. Rain gardens are one of several stormwater management practices that a homeowner can do to reduce their property's negative impact on water quality and flooding.
Photo (Above): Rain garden and rain barrel at Mason County Intermediate School.
Stormwater runoff carries pollutants like fertilizers, oil, animal waste, and dirt to local streams, lakes, and ponds and may contribute to flooding during heavy rainfall events. This puts added stress on these receiving bodies of water and their ecosystems. Excess discharge can impact streams by causing erosion, destroying habitat, and deforming natural channel flow. Ways to minimize stormwater volume leaving your property include utilizing storage devices such as cisterns or rain barrels. Contaminants discharged to streams can cause illness, impair ecological health, and increase water treatment costs. Simple practices around your home and in your neighborhood that can improve water quality include picking up pet waste, minimizing fertilizer use, and sweeping grass clippings from sidewalks and driveways.
Photo (Above): Storm drain clogged with grass clippings and debris.
Benefits of a Rain Garden
Improves water quality.
Alleviate problems associated with flooding and drainage.
Enhance the beauty of individual yards and communities.
Provide habitat and food for wildlife including birds, bees, and butterflies.
Increases infiltration which recharges the groundwater supply.
Protect against the negative effects of impervious surfaces created by development.
Rain gardens can be accommodated in almost any residential landscape. The goal is to intercept water from the source before it reaches a storm drain or water body. Sources of runoff might include impervious surfaces like your roof, sidewalk, or driveway, discharge from downspouts, or rain water that naturally flows or is mechanically diverted from uphill locations. Remember that the size, shape, and plantings can be tailored to the location and the amount of water you want to capture.
Will a rain garden integrate into the overall landscape design?
Rain gardens are temporary catchments so they may be periodically wet or dry. You will want to keep this in mind as you consider a location. They also need to be in a landscape position so that water will flow easily into the rain garden and, in the case of larger storms (rainfall is greater than 1 inch), overflow into the lawn or other area without causing damage or erosion.
Will rain garden plants fit into the landscaping scheme?
Locations with full sun will be best, but with proper plant selection partial sun locations can work as well. Rain garden plants need to be able to tolerate alternating wet and dry conditions. While there are a variety of plants suitable for rain gardens, you should consider how these plants will coordinate with the existing landscape.
How much will it cost?
The cost will be a function of the size, complexity of the draining and overflow system, and type of plantings, but in general a small residential rain garden will cost from $2-$5 per square foot if you build it yourself.
How much space do I need?
For the average residential lot, impervious surfaces total around 2400 sq. ft. A typical residential rain garden that captures about 25% of the runoff from a typical lot will be no larger than 60 sq. ft. (e.g. 6'x10'). To promote water quality, the goal is to capture the first ½” to 1” of a precipitation event within the rain garden.
How long does it take to build one?
Once you have selected the appropriate site, evaluated the soils and designed your rain garden, a rain garden can typically be constructed within a day or two. Remember to call KY 811 at 800-752-6007 before you dig, it's the law! Contact KY 811 at least two to three days prior to digging, they will come out and mark all underground utilities for free (or will advise you on who to contact, such as a local utility, to assess the site).
Features of a Rain Garden
Click on the various features of the rain garden below to learn more.
The earthen berm at the bottom of the slope is designed to hold water in the garden.
Photo (Above): Note berm at Boone County CES Rain Garden.
Downspouts can be directed to the rain garden by creating a grassy swale, creating a rock-lined channel, extending the downspout across the lawn, or by running PVC pipe underground from the downspout to the garden.
Photos (above): (left) Downspout at Kenton County CES Rain Garden; (right) downspout piped underground to Christian County DeBow Park Rain Garden.
Photo (above): Pipe underground and directed to Christian County DeBow Park Rain Garden.
A shredded hard-wood mulch is used to minimize weeds and maintain moisture in the garden. The garden will be under water after a rain so avoid using mulch that will float.
Photo (Above): Mulch being spread at Whitley County Rain Garden.
Native plants, or locally-adapted non-natives, are chosen for their non-invasive and non-aggressive growth, deep root systems, adaptation to the local environment and ability to tolerate both wet and dry soil moisture conditions. Such plants are low maintenance and many attract beneficial pollinators, birds, and butterflies.
Photo (Above): Echinacea (common name Coneflower).
Deep-rooted plants are the essential component of the rain garden, as they penetrate, break up the soil and allow water to more easily infiltrate the soil. The extensive root systems prevent soil erosion and minimize garden maintenance.
Within soils, the most important part of a rain garden, contaminants and pathogens are removed through microbial and bio-chemical processes. Soils rich in organic matter are ideal; however, most existing soils can be amended with organic matter to support plant growth and water infiltration.
Photo (Above): Boone County Rain Garden during construction.
Remove weeds and diseased plants.
Remove leaves. Rain gardens are a manmade depression and tend to collect leaves and debris and should be cleaned out in the fall. Rain gardens should not be used as a place to dump leaves. Leaves can float and block the overflow weir of a rain garden.
If Fall is excessively dry, continue to water woody species until the ground begins to freeze.
After perennials die back, dead stalks should be cut and removed from the garden. Fall removal is recommended if the plants were diseased or had insects or if you do not want the seeds from your plants to germinate. Spring removal is beneficial to allow the plants to provide winter interest of attractive seed heads and dried foliage, as well as for food and shelter for birds.
Fall is also an excellent time to check and modify your garden's overflow area (wier) if needed. Ensure no erosion is occurring, if erosion is occurring, add additional rocks or install landscape fabric to stabilize the soil.
View UK Ext. Demonstration Rain Gardens in a larger map.
The map shows rain gardens that have been installed across Kentucky. These gardens have been installed at county Extension offices and local parks. We encourage you to visit the rain gardens. Questions? Contact Ashley Osborne.