Rain Garden Instructions: What Is A Rain Garden And Rain Garden Plants
By: Heather Rhoades
Rain gardens are quickly becoming popular in the home garden. A pretty alternative to more conventional methods of improving yard drainage, a rain garden in your yard not only provides a unique and lovely feature, but can also help the environment. Making a rain garden design for your yard is not hard. Once you know how to build a rain garden and how to choose rain garden plants, you can be well on your way to having one of these unique features in your yard.
Basics of Rain Garden Design
Before you build a rain garden, you need to decide where you will be placing your rain garden. Where to place your rain garden is as important as how to build a rain garden. There are a few things to keep in mind when deciding where your rain garden will go.
- Away from the house– While rain gardens are lovely, the point of them is to help draw away water runoff. You do not want to draw water to your foundation. It is best to place rain gardens at least 15 feet (4.5 m.) away from your home.
- Away from your septic system– A rain garden can interfere with how your septic system operates so it is best to locate it at least 10 feet (3 m.) from a septic system.
- In full or part sun– Put your rain garden in full or part sun. Many rain garden plants work best in these conditions and full sun will also help water move on from the garden.
- Access to a downspout– While you should not place your rain garden near the foundation, it is helpful for water collection if you place it where you can extend a downspout out to it. This is not required, but is helpful.
How to Build a Rain Garden
Once you have decided on a location for your rain garden, you are ready to build it. Your first step after deciding where to build is how big to build. The size of your rain garden is entirely up to you, but the larger a rain garden is, the more runoff water it can hold and the more space for different rain garden plants you will have.
The next step in rain garden design is to dig out your rain garden. Rain garden instructions normally suggest making it between 4 and 10 inches (10-25 cm.) deep. How deep you make yours depends on the following:
- what kind of holding capacity you need your rain garden to have
- how wide your rain garden will be
- the type of soil you have
Rain gardens that are not wide but need to have a larger holding capacity, particularly in clay soil, will need to be deeper. Rain gardens that are wider, with smaller needed holding capacity in sandy soil, can be more shallow.
Keep in mind when determining the depth of your rain garden that the depth starts at the lowest edge of the garden. If you are building on a slope, the lower end of the slope is the starting point for measuring the depth. The rain garden should be level across the bottom of the bed.
Once width and depth are determined, you can dig. Depending on the size of the rain garden, you can hand dig or rent a back hoe. Soil removed from the rain garden can be mounded up around 3/4 of the bed. If on a slope, this berm goes on the lower end of the slope.
After the rain garden is dug, if possible, connect a downspout to the rain garden. This can be done with a swale, an extension on the spout, or through an underground pipe.
Rain Garden Plantings
There are many plants you can use for rain garden plantings. The list below of rain garden plants is just a sample.
Rain Garden Plants
- Blue flag iris
- Bushy aster
- Cardinal flower
- Cinnamon fern
- Dwarf cornel
- False aster
- Fox sedge
- Grass-leaved goldenrod
- Heath aster
- Interrupted fern
- Lady fern
- New England aster
- New York fern
- Nodding pink onion
- Maidenhair Fern
- Ohio goldenrod
- Prairie blazingstar (Liatris)
- Rough goldenrod
- Royal fern
- Smooth penstemon
- Stiff goldenrod
- Black-eyed susan
- Joe-pye weed
- Tufted hairgrass
- Virginia mountain mint
- White false indigo
- White turtlehead
- Wild columbine
- Wild quinine
- Yellow coneflower
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Read more about Garden Spaces
A rain garden is a depressed area in the landscape that collects rain water from a roof, driveway or street and allows it to soak into the ground. Planted with grasses and flowering perennials, rain gardens can be a cost effective and beautiful way to reduce runoff from your property. Rain gardens can also help filter out pollutants in runoff and provide food and shelter for butterflies, song birds and other wildlife.
More complex rain gardens with drainage systems and amended soils are often referred to as bioretention.
Note: Refer to the links in this section for important tips on how to locate your rain garden. These include areas to avoid and the need for accurate information about underground utilities before you begin to dig.
Mary Bohling, Michigan State University Extension and Cynthia Ross, Friends of the Rouge - July 29, 2013
Step-by-step guide to planning and planting rain gardens helps prevent water pollution.
Rainwater can add to water pollution. When rainwater flows over hardened, impervious, surfaces like sidewalks, rooftops and parking lots, it collects oils, soaps, fertilizers and other pollutants on its way to our sewer systems. During periods of heavy rain in highly urbanized areas, like much of Southeast Michigan, the contaminated rainwater can flow directly into waterways such as the Rouge and Detroit Rivers. Strategically placed rain gardens can help contain rainwater before it gets into the waterways. The new Step-by-Step Guide to Planning and Planting Rain Gardens in Detroit is a great resource for people who want to create rain gardens, in not only Detroit, but also elsewhere. According to the guide, when Detroit neighborhoods were built, they used one sewer system to carry wastewater from homes and rainwater from streets to the wastewater treatment plant. As the population grew, sewer lines filled to capacity. When pipes are full, they overflow into the Rouge and Detroit Rivers to prevent sewage from backing up in residential basements.
The guide was developed to be one of the easiest and most concise resources on rain gardens in the Detroit area. The guide breaks down the process of planning and planting a rain garden with photos and information for each of the eight steps, as well as sample planting plans (e.g., full sun plan, partial shade plan):
2) Determine the garden size
3) Choose native plants suited for the site
4) Prepare the garden area
6) Cover with an organic mulch
7) Disconnect downspouts & direct rainwater to the garden
8) Maintain your garden over time
By following these eight steps, your rain garden will decrease the amount of rainwater that flows off your property and into the sewers, while you can help prevent water pollution. According to Michigan State University Extension, this process will allow us to disconnect our home downspouts from the sewer system and directing the water into a beautiful rain garden.
This guide makes it easier for people who want to build rain gardens to do so, and by creating rain gardens, they can do their part to prevent water pollution in our local waterways and the Great Lakes.
For a copy of the guide, contact Cynthia Ross at Friends of the Rouge or Melissa Damashchke at the Sierra Club Great Lakes Program. Supplemental information with a native plant list and sample rain garden designs are also available.
This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).
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Rain Garden Plant Lists and Designs
Both of the below rain garden designs are meant for a 12 x 24-foot space, but are also adaptable to smaller areas.
Note: In the below plant lists, some plants are linked to our Growing Guides with pictures. Others can be easily found via Google.
Rain Garden for Sun
Plants set into a rain garden that gets full sun must be able to endure both occasional flooding and dry spells.
Sun Rain Garden Plant List
In the center, plant #1 to #6. For the drier, outer edge, plant #7 to #14.
- Summersweet (Clethra alnifolia ‘Ruby Spice’), a woody shrub that bears fragrant, pink, bottlebrush flowers in the summer. 5 to 6 feet tall Zones 4 to 9. One plant.
- Red osier dogwood (Cornus sericea), which has white blossoms in spring and reddish-purple leaves in the fall—although its most attractive features are its red stems, which lend winter interest to the landscape. 6 to 10 feet tall Zones 2 to 8. One plant.
- Blue flag iris (Iris versicolor), which brightens the rain garden with lavender-blue flowers in the spring. It looks very natural in a wet setting. Avoid the yellow flag iris (Iris pseudacorus), which is an invasive species that will take over. 2 to 4 feet tall Zones 3 to 9. Four plants.
- Joe Pye weed (Eupatorium maculatum), which has purple flowers in late summer that butterflies can’t resist. 3 to 5 feet tall Zones 3 to 7. Two plants.
- Astilbes (Astilbe), which are long-lived, moisture-loving perennials that will thrive in the sunny rain garden if planted where they get some afternoon shade from taller shrubs nearby. They bloom in summer and are available in pinks, reds, purple, and white. 1 to 3 feet tall Zones 3 to 8. Three plants.
- Daylilies (Hemerocallis), which may not be natives but can keep your rain garden in bloom over a long season if you plant early, midseason, and late varieties. Assorted heights and a rainbow of colors are available. Zones 4 to 11. Five plants.
- Blueberries (Vaccinium), whether highbush (up to 5 feet tall) or lowbush (up to 2 feet tall) varieties, which add both a flowering shrub and an edible fruit to your landscape. Zones 3 to 8. Two plants.
- American cranberry (Vaccinium macrocarpon), which is a pretty, ground-covering shrub that also bears edible fruit. About 6 inches tall Zones 2 to 7. Six plants.
- Bee balm (Monarda), which in summer features brilliant-red, pink, or white flowers that attract hummingbirds and butterflies. Look for a mildew-resistant variety. 3 feet tall and wide Zones 3 to 9. Two plants.
- New England aster (Aster novae-angliae), which will carry the show into fall with its bright, violet-purple flowers. It gets quite tall but can be cut back to half its height in June to create a shorter and bushier plant, if desired. Up to 6 feet tall Zones 4 to 8. Two plants.
- Sneezeweed (Helenium autumnale), which bears sunny yellow flowers in late summer. It is highly adaptable to wet or dry soil. 3 to 5 feet tall Zones 4 to 8. One plant.
- Meadow anemone (Anemone canadensis), which is deer-resistant and salt-tolerant. This tough little perennial bears pure-white blossoms in late spring. 2 feet tall Zones 2 to 9. Two plants.
- Blue cardinal flower (Lobelia siphilitica), which has spikes of true blue flowers in late summer. 2 to 4 feet tall Zones 5 to 9. Six plants.
- Butterfly weed (Asclepias tuberosa), which features orange blossoms that provide excellent nectar for butterflies. In addition, the plants are an important larval food for monarch butterflies. 2 to 3 feet tall Zones 4 to 9. Three plants
Rain Garden for Shade
Placing a rain garden in full shade is not recommended partial shade is best.
Shade Rain Garden Plant List
In the center, plant #1 to #6. For the drier, outer edge, plant #7 to #14.
- Rhododendrons, especially cold-hardy native rhodora (Rhododendron canadense), which like damp soil and partial sun. They will bloom profusely in the spring. 2 to 4 feet tall and wide Zones 3 to 6. Two plants.
- Winterberry (Ilex verticillata), which needs one male plant to act as a pollinator, along with the females, if you want a crop of colorful red berries. For this garden size, choose from dwarf cultivars. 3 to 5 feet tall Zones 3 to 9. Two plants.
- Cardinal flower (Lobelia cardinalis), which grows well in sun or partial shade. It has rich red flowers in late summer. 2 to 3 feet tall Zones 3 to 9. Six plants.
- Pink turtlehead (Chelone lyonii), which is a trouble-free perennial that doesn’t mind wet feet. It blooms in the late summer to early fall. 2 to 4 feet tall Zones 3 to 8. Seven plants.
- Purple meadow rue (Thalictrum dasycarpum), which loves a damp spot in partial shade. It can get quite tall and has clouds of purple-tinged white blossoms in summer. 3 to 6 feet tall Zones 5 to 9. Two plants.
- Wild columbines (Aquilegia canadensis), which are an important source of nectar for hummingbirds and butterflies and thus will draw them to your rain garden. They produce their bicolor red and yellow blossoms in late spring. 1 to 3 feet tall Zones 3 to 8. Five plants.
- Arrowwood (Viburnum dentatum), which is a nicely rounded shrub with glossy leaves and dark blue berries. It has creamywhite blossoms in late spring and colorful fall foliage. 6 to 10 feet tall and wide Zones 3 to 8. One plant.
- Dwarf fothergilla (Fothergilla gardenii), which has fragrant white flowers that appear before the plant leafs out in the spring. The foliage becomes a neat, crimson mound in the fall. 3 feet tall and wide Zones 5 to 9. One plant.
- Common bearberry (Arctostaphylos uva-ursi), which is a rugged evergreen ground cover in the heath family. It has white flowers in spring and red berries in late summer. 3 to 8 inches tall, spreading to between 2 and 4 feet wide Zones 2 to 6. Five plants.
- Coral bells (Heuchera sanguinea), which are colorful foliage plants that send up tall spikes of tiny red, pink, or white flowers in late spring. 6 to 12 inches high and wide Zones 3 to 8. Seven plants.
- Foam flower (Tiarella cordifolia), which is a deer-resistant plant with white flowers in spring. (Heuchera and Tiarella have been crossed to create a hybrid genus called Heucherella which combines the gorgeous foliage of heucheras with the showy flowers of tiarellas—look for this one!) 5 to 12 inches tall Zones 3 to 7. Five plants.
- Jacob’s ladder (Polemonium reptans), which is a low-growing, spreading perennial with clusters of light-blue flowers. 8 to 12 inches tall Zones 3 to 8. Three plants.
- Zigzag goldenrod (Solidago flexicaulis), which bears golden yellow flowers in the fall. 2 feet tall and wide Zones 3 to 8. Three plants.
- Spotted geranium (Geranium maculatum), which has dainty, pinkish-purple flowers that bloom above the mound of lobed leaves in the spring and often again in the fall. 1 to 2 feet tall Zones 4 to 8. Six plants.
Learn to build a Pacific Northwest rain garden
Rain gardens are a great way to both have an attractive landscape feature and also enhance water quality in the drizzly Pacific Northwest. Forests and soils act as a filter for rainwater, cleaning it and releasing it slowly into creeks, streams, wetlands, lakes and eventually the ocean. Rain that falls on solid surfaces such as sidewalks, roads and roofs, collects the pollutants on these surfaces, bypassing the natural filter process, and carries them directly into waterways such as the Columbia River.
As more land is developed for human use, the amount of impervious surface increases, delivering ever more polluted runoff to these water bodies, where we swim, fish and play.
Rain gardens are designed to gather, soak up and filter rainwater coming from any surface water can’t move through. They function as temporary ponds, filling with the water running off these surfaces, holding it and allowing it to soak into the soil where it is filtered and cleaned. In this way, rain gardens prevent pollutants from reaching natural water bodies.
These special gardens add external appeal to the home landscape, reduce flooding and erosion issues, create habitat for wildlife and recharge local groundwater.
With careful planning and some sweat equity, homeowners can install their own rain garden. Selecting an appropriate site is important so check with your municipality on specific regulations and to have existing utilities located.
A rain garden should be placed where it can drain selected hard surfaces efficiently, but it should be at least 10 feet from any building foundations. Other things to avoid are buried utilities, steep slopes, septic tank and well areas, existing intact natural areas, and spots with high existing groundwater. You’ll also need to find out how fast the soil of your rain garden drains.
When building a rain garden, a variety of tools and materials are needed for things like marking the garden shape, excavating, planting and mulching. You may also need soil or soil amendments depending on the type of existing soil in the location. Drain rock, gravel and larger rocks or boulders will also be very useful. You’ll also need mulch and some fabulous plants!
Your rain garden should include an entry point for water coming from the hard surfaces you are draining. This might be a downspout, pipe, or perhaps a dry creek bed connecting the spaces. The size of the garden will be determined by the size of the area it is draining and how quickly your soil drains. The garden will need a level, excavated bottom, an overflow point, and properly prepared soil. Water entry and exit points must be lined with drain rock and possibly larger rocks to prevent erosion and silt movement as the water moves into and out of the garden.
There are many great plants that will grow happily in rain gardens, which are divided into three planting zones. Zone 1 is the bottom of the garden plants here need to be very tolerant of wet conditions. Zone 2 plants are on the side slopes of the garden and need to handle occasional standing water. Zone 3 is the top edges and perimeter of the garden. Plants growing here must do well with normal to dry soil conditions. There are many lovely plants both for sun and shade that can be included. Selecting plants that are drought tolerant once established will allow your rain garden to function without supplemental water. The first one or two years, you will need to provide some extra water for young plants to help them develop and ‘stand on their own roots’ without extra water support.
Select a mix of plant types – small trees, shrubs, and perennials. Remember to base your selections on their mature size to avoid overcrowding. Ultimately, a mature rain garden should have 90 to 100% of its bottom covered with plants. Narrow your choices based on your individual preferences and interests. Grasses and grass-like plants, evergreens, plants for beneficial insects and wildlife, fragrant flowers, natives — there are many options for multi-seasonal beauty!
After your garden is planted, it should be mulched with a good quality natural wood mulch — avoid colored mulches, grass clippings, and mulch from questionable source wood like chemically treated pallets. Place a sturdy drain rock layer around the entry and exit points instead of mulch. You can also add extra rocks — gravel, boulders and the like — to create accents here and there in the garden, enhancing its natural look.
As your rain garden matures, you’ll need to do routine maintenance to keep it looking attractive year-round. Avoid using fertilizers and pesticides in your rain garden if possible. Weeding will always be necessary but should lessen as plants take up more space. Occasional top-dressing mulch, seasonal pruning and cleanup might be necessary as well as removal of any general debris which falls into the garden. Watch out for erosion, areas where this occurs should be repaired and stabilized with extra drain rock and larger rock pieces if necessary.
Your personal rain garden can do great things for your own garden happiness and home environment. The awesome bonus is it also does great things for the health of the very special part of the country we live in!
To learn more about rain gardens, attend the upcoming “Let it All Soak In: A Rain Garden Webinar” on April 13. A stunning landscape feature and stormwater device all in one, rain gardens are a unique way to protect the water quality of your local creek, lake or the Columbia River while spiffing up the garden at the same time. Come away with a solid understanding of rain gardens — their benefits, suitable locations and tools for design and installation.
Attendees will learn about rain garden plants for sun and shade and become familiar with the Rain Garden Handbook for Western Washington Homeowners. After this 90-minute webinar by Colleen Miko, you’ll be ready to tame the rain.
This webinar is put on by the WSU Clark County Extension Master Gardener Program in collaboration with Clark County Public Health – Solid Waste Outreach.
“Let it All Soak In: A Rain Garden Webinar,” 6:30-8 p.m., Tuesday, April 13 free, register in advance at https://wsu.zoom.us/meeting/register/tJYlfu-srzkqH9AtbW_8wyM515rxu15EngMa. After registering, you will receive a confirmation email with information about joining the meeting. Contact [email protected] or 564-397-5738 for more information.
— Christine Anderson is a Washington State University Extension Clark County master gardener
Choosing Plants for a Rain Garden
Proper rain garden design dictates that all plants must be perennial. This is due to the way a rain garden functions as a water abatement feature, which depends on the deep roots of perennial plants.
Plants that you install in the center of the garden will experience longer periods of wet soil and must be able to thrive in these moist conditions. Five hardy and long-blooming plants you can't go wrong with include false indigo coneflower hardy hibiscus black-eyed Susan hardy geranium (cranesbill) and hardy grasses, such as fountain grass or corkscrew rush
Plants around the edge of the rain garden will rarely have wet feet and won't mind occasional periods of drought. Some attractive flowering choices with big wildlife appeal include gaura, coral bells, yarrow, butterfly weed, and catmint
What is a rain garden? How do rain gardens work?
A rain garden is a shallow area designed to collect and filter stormwater runoff. Rain gardens catch water that would have flowed into the street or flooded your yard, and they naturally clean and release that water into the soil.
Rain garden benefits
Rain gardens are amazing structures that help us and the environment. They:
- Protect nearby lakes, rivers or ponds by collecting and filtering runoff before it can reach these areas
- Help prevent soil erosion, i.e., the wearing down of topsoil in your yard
- Help prevent potential floods by reducing the amount of water that ends up in a storm drain
- Can enhance your property value, since they’re both functional and attractive
How to build a rain garden in your yard
Step 1: Decide on rain garden placement
- Find out where water is coming from (like your roof or driveway) and where it goes (like a sunken spot in your yard, or the street) after a storm. Your garden should sit somewhere between the two.
- Ensure the spot is at least 10 feet away from your home, and at least 25 feet away from a septic system. Also, confirm there are no underground utilities in the spot you’ve chosen. If you’re not sure, call 811 to find out.
- Make sure the location gets full or at least partial sunlight.
Step 2: Check the soil
This step is super important because good soil is what makes or breaks a rain garden. Rain garden soil must be well-draining in order for the garden to do its job. To test your soil:
- Dig a hole about a foot deep and fill it with water. Ideally, the water should drain within 12 hours, and 24 hours at the absolute most. If it does, you picked a good spot—move on to step 3!
- If the water didn’t drain within a day or less, consider a different location. Soil types can vary quite a bit even within the same yard, so there may be a more suitable spot nearby. It's also possible to work with what you have. Vertical mulching can help loosen soil, and you can improve the soil with the right tools and amendments. If you need help prepping your soil for a rain garden,
Step 3: Choosing plants for rain gardens
- Your rain garden should be filled with plants native to your region. Do some research to figure out what plants meet that need. For help, you can contact your local county extension office—they'll likely have a ready-to-use list of native plants.
- Select a mix of plants with different colors, heights, and bloom times to add dimension to your garden. Check out this blog post for rain garden design ideas.
Step 4: Size it out
- Rain gardens are usually sized anywhere from 100 to 300 square feet. To figure out what’s best for your yard, note that a rain garden can typically handle runoff from a surface 3 times its size. So, say your rain garden will be expected to collect runoff from a section of your roof that’s 600 square feet. To accommodate, your rain garden should be about 200 square feet in size.
Step 5: Construct your garden
With your location, flowers and size figured out, it’s time to dig.
- Use the rope to layout the size and shape of the garden. Most rain gardens are bean-shaped.
- Dig a flat hole about 4 to 8 inches deep. Make sure the bottom of the garden is leveled. Add compost or sand if needed and work it into the soil. If you aren’t adding materials, just till the soil to loosen it up.
- Add your plants, fill the garden back up with the leftover soil, and mulch the area.
Will a rain garden attract mosquitos?
Nope! Since water in rain gardens drains quickly, mosquitos aren’t drawn to them. They’d much rather hang around standing water that stays in place for a while, like in a birdbath.