What is a Rain Garden?
A rain garden is a colorful, perennial planting designed to capture and use rain water that may otherwise run off. It is a garden in a shallow depression. It can be large or small. A rain garden is not a wetland and should not hold water for more than a few hours, or a day at most. It is not a breeding ground for mosquitoes.
Why Plant a Rain Garden?
A rain garden…
- Captures and filters runoff. Limited rains fall hard and fast. Runoff from roofs, lawns, and drives may overload storm sewers and pollute streams.
- Reduces the need for supplemental water. Water is often limited in the Great Plains. Maintaining a green and colorful yard with rural or municipal water can be expensive.
- Grows healthy plants using good water. Rain is high quality water, good for plants; while well water may be poor for plant health.
- Provides changing colors and textures. A mix of plants changes color, structure, shape and form throughout the season.
- Provides habitat. Forbs and grasses in rain garden are attractive to butterflies, bees, birds, and other wildlife.
Where Should a Rain Garden be Established?
Locate a rain garden to intercept runoff from roofs, yards, drives, or streets. Choose a low or wet spot in your yard where water drains naturally. The closer to the street the better the spot. It should not be built within ten feet of foundation walls or on poorly drained sites. A rain garden should not be built over buried utilities or where mature plants could obstruct overhead utilities or drivers’ vision. Do not construct a rain garden where prohibited by local ordinances or where subject to disturbance.
How to Build a Rain Garden
Most rain gardens can be constructed with equipment available to homeowners such as shovels, rakes, and rototillers. A small rain garden of simple design can be built in a day.
- Do your homework first. Many design manuals are available, online and at public offices. You can even pick one up at Brown SWCD free of charge. In addition, several are listed in the reference section below.
- Locate a proper site.
- Check the soil. Sand-based soil works well. Clay soil gardens are not recommended.
- Calculate square footage draining to the rain garden (from roof, yard, drive, etc).
- Mark outline of rain garden. You can use a garden hose to help. Rain garden area should equal about 10% of the drainage area. Any shape is fine. Irregular margins are often more attractive.
- Evaluate soil compaction, texture, and infiltration.
- After checking for underground power lines and other utilities, dig a 4-8 inch deep basin with a flat bottom. Excavated material can be placed on the downhill side or moved off site. Avoid compaction during construction.
- Loosen 6-12 inches of the natural soil below the bottom of the rain garden.
- Large designs or sites with high clay content soils may require over-digging the basin 1-2 feet deep, back filling with a well-blended mixture of 70% sand and 30% organic matter, and shaping the top of this material into a 4-8 inch deep basin.
- Slope and pack any created berms, leaving a gentle slope that will be easy to maintain.
- Smooth, seed berm, and plant the rain garden.
- Choose native plants and cultivars that tolerate drought and occasional drenching. Use potted or bare root plants rather than seeds. As a general rule of thumb, plants should be about 18 inches apart, or one plant per 2.5 square feet.
- Apply shredded wood mulch as desired to conserve water and control weeds. Shredded mulch stays in place better than wood chips.
- Water and weed to establish plants.
- Mow or remove the dead vegetation each spring, or burn it off if local ordinances allow. Weed three times per growing season. (Tree seedlings are usually the most abundant weeds.)
What to Plant in a Rain Garden
Rain gardens can be planted to native or non-native species of flowers, grasses, shrubs, and trees. Do not plant species considered invasive. Consider the growth habit and mature size of the species. Some native species are deep rooting and encourage infiltration of runoff water. Native species are adapted to local conditions and may be more tolerant of diseases and drought, compared to some non-native species. A diversity of plant species will provide an array of color and texture, and attract a variety of insects and wildlife. Disease and insects may destroy an entire rain garden if planted to a single species. Plants requiring constant moisture should not be planted in a rain garden. Use locally adapted species and varieties.
How to Maintain a Rain Garden
Very little additional water or weeding is needed once a rain garden is established. Supplemental water is usually needed only to establish plants and during drought. Apply and renew mulch as needed to control weeds and conserve water. Leave vegetation standing over winter for snow catch, textural diversity, and visual interest. In early spring, remove previous year’s growth by mowing or clipping before new growth initiates.
References and more rain garden information:
- “Living Landscapes in North Dakota: A Guide to Native Landscaping” a North Dakota NRCS publication.
- “Rain Gardens – A How-To Manual for Homeowners” a Wisconsin DNR and US Geological Survey publication.
- Rice Creek Watershed District Rain Gardens Information
- Maplewood, Minnesota Rainwater Gardens