Rain Gardens

Rain Gardens (1)

Photo: Maplewood, MN Rain Gardens

Already have a rain garden or thinking of installing one? Let us know! We’d be interested in your comments, the success of your garden, and pictures of your progress. Please send information to Amanda Meder, Watershed Management Division, Public Works and Utilities Department, 901 North 6th Street, Lincoln, NE 68508, 402-441-7075 or

What is a Rain Garden?

A rain garden is a garden of native shrubs, perennials, and flowers planted in a small depression, which is generally formed on a natural slope. It is designed to temporarily hold and soak in rain water runoff that flows from roofs, driveways, patios or lawns. Rain gardens are effective in removing up to 90% of nutrients and chemicals and up to 80% of sediments from the rainwater runoff. Compared to a conventional lawn, rain gardens allow for 30% more water to soak into the ground. It is not a pond or wetland, but is dry most of the time and typically holds water during and following a rainfall event.

Why is rainwater runoff a problem?

Every time it rains, water runs off impermeable surfaces, such as roofs or driveways, collecting pollutants such as particles of dirt, fertilizer, chemicals, oil, garbage, and bacteria along the way. The pollutant-laden water enters storm drains untreated and flows directly to nearby streams and ponds. EPA estimates that pollutants carried by rainwater runoff account for 70% of all water pollution. Rain gardens collect rainwater runoff, allowing the water to be filtered by vegetation and percolate into the soil. These processes filter out pollutants.

Is there a difference between a rain garden and a regular garden?

In the design of a rain garden, typically six to twelve inches of soil is removed and altered with tillage, compost and sand to increase water infiltration. The type of alteration to the soil depends on the current soil type, so it is a good idea to obtain a soil test. Rain gardens are generally constructed on the downside of a slope on your property and collect rainwater runoff from the lawn, roof and/or the driveway. Once water collects in the rain garden, infiltration may take up to 48 hours after a major rainfall. Also, rain gardens incorporate native vegetation; therefore, no fertilizer is needed and after the first year, maintenance is usually minimal.

What are the benefits?

  • Improves water quality by filtering out pollutants
  • Aesthetically pleasing
  • Preserves native vegetation
  • Provides localized stormwater and flood control
  • Attracts beneficial birds/butterflies/insects
  • Easy to maintain after establishment
  • What is the Average Size and Placement of a Rain Garden?

A rain garden should have an area about 20% the size of the roof, patio, or pavement area draining into it. A typical residential rain garden is between 100 and 300 square feet. If a smaller rain garden than recommended for a lot is chosen, it will still function, as any size garden can make an impact.

Rain gardens are longer than they are wide and are perpendicular to the slope, in order to catch the maximum amount of rainfall. Rain gardens should be placed at least 10 feet away from building foundations and should not be located where water ponds for an extended period of time.

What types of plants are used?

As a rule, native vegetation should be incorporated into a rain garden. Native plants don’t require fertilizer, have good root systems, and are better at utilizing the water and nutrients available in their native soils than non-native species. Perennials, shrubs, wildflowers, or a mixture of all three can be planted. Avoid planting trees, as trees generally absorb more water than surrounding plants. Also, never plant invasive or noxious species in a rain garden, such as purple loosestrife.

What is the cost of a rain garden?

The cost of a rain garden is dependant on the property’s soil type, the size of roof/driveway/patio draining into a rain garden, and the types of plants chosen. If the soil is high in clay content, it may be a good idea to install an under drain system to prevent standing water in the rain garden for more than 48 hours.

For a self-built rain garden, expect to pay between $3 and $5 per square foot in plant costs and soil amendments. Digging the garden is the most time consuming task, as 6-8 inches of soil depth is typically removed to add amendments.

When working with a landscaping company to design and install a rain garden, the cost will significantly increase to around $10 to $12 per square foot.

What kind of maintenance is involved?

Rain gardens do not require fertilizer, if native vegetation is used. During the first few years after the installation of a rain garden, the weeds will need to be removed periodically. After the plants in the rain garden have become established and grown larger, they will eventually out-compete the weeds. As the rain garden is establishing during the first and second year or during periods of little to no rainfall, occasional watering of the plants will be necessary.

Why is the City of Lincoln promoting rain gardens?

The main function of a rain garden is improving water quality. Communities around the country have experienced dramatic reductions in stormwater pollution, due to many homeowners installing rain gardens on their property. According to the EPA, 70% of all water pollution comes from pollutants carried in rainwater runoff and other non-point pollution sources. Rain gardens are effective in removing up to 90% of pollutants and 80% of sediments from individual properties. Not only are rain gardens beautiful additions to any landscape, the amount of pollution leaving yards and entering nearby streams, lakes, and wetlands can be reduced. Constructing, installing, and maintaining a rain garden will be helping to reduce pollution and keep our streams and lakes healthy.


Rain Garderns (2)

From Wikipedia, the free encyclopedia

Business parking lot that drains to a rain garden. A sunken curb retains asphalt, yet lets water flow off the edges.

Business parking lot that drains to a rain garden. A sunken curb retains asphalt, yet lets water flow off the edges.

A rain garden is a planted depression that is designed to absorb rainwater runoff from impervious urban areas like roofs, driveways, walkways, and compacted lawn areas. This reduces rain runoff by allowing stormwater to soak into the ground (as opposed to flowing into storm drains and surface waters which causes erosion, water pollution, flooding, and diminished groundwater).[1] Rain gardens can cut down on the amount of pollution reaching creeks and streams by up to 30%.

Native plants are recommended for rain gardens because they generally don’t require fertilizer and are more tolerant of one’s local climate, soil, and water conditions. The plants — a selection of wetland edge vegetation, such as wildflowers, sedges, rushes, ferns, shrubs and small trees — take up excess water flowing into the rain garden. Water filters through soil layers before entering the groundwater system. Root systems enhance infiltration, moisture redistribution, and diverse microbial populations[2] involved in biofiltration. Also, through the process of transpiration rain garden plants return water vapor into the atmosphere. A more wide-ranging definition covers all the possible elements that can be used to capture, channel, divert, and make the most of the natural rain and snow that falls on a property. The whole garden can become a rain garden, and all of the individual elements that we deal with in detail are either components of it, or are small-scale rain gardens in themselves.

The concept of a rain garden began in the 1990s in the state of Maryland. They are now one of the fastest growing areas of interest for home landscapes.

Mimicking natural systems

Before an area is developed, a natural groundwater filtering process takes place. Rainwater flows into low places, where native plants soak up and transpire a small portion of the water. The rest percolates into the ground. In a natural environment such as this, streams and creeks are fed by cool groundwater at a fairly constant rate. This water is buffered by groundwater storage capacity, ion exchange with substrates, and microbial processes within soil. Unfortunately, in most urban environments, the water system no longer works this way. Rain gardens can mimic some of this natural system.

Rain gardens increase infiltration, decrease surface run-off from roofs, roads, and paved areas, and may cumulatively reduce the frequency of flash flooding. Not all subsurface water percolates down to the ground water. Plant transpiration, often accelerated by urban heat island effects, speeds evaporation that frees water storage capacity within surface soil even as water continues percolating from saturated soil below. This is particularly true where mulch or debris inhibit direct evaporation from a soil surface. Root and microbial exudates, eg. saccharides, can raise soil’s volumetric water holding capacity and retention coefficients for many contaminants. All this promotes natural biofiltration processes.

Surface run-off not absorbed in the rain garden slows significantly—due to the swale and vegetative barrier—which reduces sediment load and pollution downstream. Because water moves slower in the ground than it does over the urban hardscape, rain gardens mitigate peak flow more than just by reducing the volume of water reaching the outlet.

Mitigating the impact of urban development

In developed areas, the natural depressions are filled in. The surface of the ground is leveled or paved, and water is directed into storm drains. This causes several problems. First of all, streams that are fed by storm drains are subjected to sudden surges of water each time it rains[3][4][5], which contributes to erosion and flooding. Also, the water is warmer than the groundwater that normally feeds a stream, which upsets the delicate system. Warmer water cannot hold as much dissolved oxygen (DO). Many fish and other creatures in streams are unable to live in an environment with fluctuating temperatures. Finally, a wide variety of pollutants[6] spill or settle on land surfaces between rain events. The initial rinse from each runoff event can wash this accumulation directly into streams and ponds.

Excess water from an expanding area or increasing development density is cumulative. Flooding results from ever smaller events requiring upgrades of drainage infrastructure. Areas compacted by heavy equipment during past construction activities remain less permeable long after vegetation is reintroduced. Both groundwater recharge and subsurface flow paths are disrupted. Strategies to retain water and soil at their source can slow this harmful cascade.

Rain gardens may be located near a drainpipe from a building’s roof (with or without rain barrels), although if there’s a basement, a French drain may be used to direct the rainwater to a location farther from the building. Normally, a rain garden—or a series of rain gardens—is the endpoint of drainage, but sometimes it can be designed as a pass-through system where water will percolate through a series of gravel layers and be captured by a drain under the gravel and carried to a storm water system. Rapid pass through systems reduce peak discharge and extend hydraulic lag time of the discharge —reversing urbanization’s major hydraulic impact. However, rapidly drained systems do not achieve pollution removal rates that more slowly percolating rain gardens do[7].

Runoff volumes from impervious surfaces in many urban cities make green roofs necessary to reduce peak volumes to magnitudes that areas available for rain gardens can handle. While some rain garden wash through is acceptable from heavy storms that dilute pollution, depression focused recharge of contaminated runoff is avoided by proper rain garden design. The simplest fail safe for handling polluted runoff is for a garden with one inlet not to accept more volume than it can handle, and not pond to sufficient depth to push water into the water table faster than required for adequate biofiltration.

Rain gardens are beneficial for many reasons: improve water quality by filtering run-off, provide localized flood control, aesthetically pleasing, and provide interesting planting opportunities. They also encourage wildlife and biodiversity, tie together buildings and their surrounding environments in attractive and environmentally advantageous ways, and provide significant partial solutions to important environmental problems that affect us all.

A rain garden provides a way to use and optimize any rain that falls, reducing or avoiding the need for irrigation. They allow a household or building to deal with excessive rainwater runoff without burdening the public storm water systems. Rain gardens differ from retention basins, in that the water will infiltrate the ground within a day or two. This creates the advantage that the rain garden does not allow mosquitoes to breed.


The first rain gardens were created to mimic the natural water retention areas that occurred naturally before development of an area. The rain gardens for residential use were developed in 1990 in Prince George’s County, Maryland, when Dick Brinker, a developer building a new housing subdivision had the idea to replace the traditional best management practices (BMP) pond with a bioretention area. He approached Larry Coffman, the county’s Associate Director for Programs and Planning in the Department of Environmental Resources, with the idea.[8] The result was the extensive use of rain gardens in Somerset, a residential subdivision which has a 300-400 ft² rain garden on each house’s property.[9] This system proved to be highly cost-effective. Instead of a system of curbs, sidewalks, and gutters, which would have cost nearly $400,000, the planted drainage swales cost $100,000 to install.[8] This was also much more cost effective than building BMP ponds that could handle 2-, 10-, and 100-year storm events.[8] Flow monitoring done in later years showed that the rain gardens have resulted in a 75-80% reduction in stormwater runoff during a regular rainfall event.[9]

This is also referred to as Low Impact Development (LID), and is cited by the EPA on their website as a success on the Stormwater Case Studies section of their website.[10] This webpage has many links to information on Prince George’s County’s literature on implementing Low Impact Development (LID) in a community.

Some de facto rain gardens predate their recognition by professionals as a significant LID tool. Any shallow garden depression implemented to capture and retain rain water within the garden so as to drain adjacent land without running off a property is at conception a rain garden–particularly if vegetation is maintained with recognition of its role in this function. Vegetated roadside swales, now promoted as “bioswales” remain the conventional drainage system in many parts of the world from long before extensive networks of cement sewers became the conventional engineering practice in the USA.

What is globally new about such technology is the emerging rigor of increasingly quantitative understanding of how such tools may make sustainable development possible. This is as true for wealthy developed communities retrofitting bioretention into built stormwater management systems, and for developing communities seeking a faster and more sustainable development path.


A rain garden requires an area where water can collect and infiltrate, and plants to maintain infiltration rates, diverse microbe communities, and water holding capacity. Transpiration by growing plants accelerates soil drying between storms. This includes any plant extending roots to the garden area.

Simply adjusting the landscape so that downspouts and paved surfaces drain into existing gardens may be all that is needed because the soil has been well loosened and plants are well established. However, many plants don’t tolerate saturated roots for long and often more water runs off one’s roof than people realize. Often the required location and storage capacity of the garden area must be determined first. Rain garden plants are then selected to match the situation, not the other way around.

Soil and drainage

When an area’s soils are not permeable enough to let water drain and filter properly, the soil in the bottom of the garden is replaced with soil that will help the water to drain, typically containing 60% sand, 20% compost, and 20% topsoil. Deep plant roots create additional channels for storm water to filter into the ground. Sometimes a drywell area with a series of gravel layers may be constructed near the lowest spot in the rain garden to facilitate percolation. However, putting a drywell in the lowest spot washes in maximum silt to clog it prematurely and can make the garden into a rapid infiltration basin without the intended 100% retention of small rain events that rain gardens are designed to achieve. Depression focused recharge of polluted water into wells poses serious ground water pollution threats. Similarly combining septic treatment adjacent to rain gardens warrants careful review by a qualified engineer. Dirtier water must be more completely retained in soil to be purified. This usually means more small rain garden basins and greater required soil depths to the seasonal high watertable. In some cases lined bioretention cells with subsurface drainage are used to retain small events and filter larger ones without letting water percolate deeply on site. If this leachate is not to receive further treatment, the soil media warrants careful attention to achieve water quality goals.

Rain gardens are at times confused with bioswales. Swales slope to a destination, while rain gardens do not; however, a bioswale may end with a rain garden. Drainage ditches may be handled like bioswales and even include rain gardens in series, saving time and money on maintenance. If most the water volume flowing into a garden, flows out again then rain garden may be the wrong term. Similarly, part of a garden that nearly always has standing water is a water garden, wetland, or pond not a rain garden. These semantics clarify where certain rain garden functions are achieved. One combines landscape elements to achieve objectives.

Plant selection

Plants selected for use in a rain garden should tolerate both saturated and dry soil. Using native plants is generally encouraged. This way the rain garden may contribute to urban habitats for native butterflies, birds, and beneficial insects.

Well planned plantings require minimal maintenance to survive, and are compatible with adjacent land use. Trees under power lines, or that up heave sidewalks when soils become moist, or whose roots seek out and clog drainage tiles can cause expensive damage.

Trees generally contribute most when located close enough to tap moisture in the rain garden depression, yet do not excessively shade the garden. That said, shading open surface waters can reduce excessive heating of habitat. Plants tolerate inundation by warm water for less time because heat drives out dissolved oxygen, thus a plant tolerant of early spring flooding may not survive summer inundation.


Rain Gardens (3)


What is a Rain Garden?

A rain garden is an attractive garden with a special purpose; to reduce the amount of stormwater entering our beautiful Great Lakes.

A rain garden is constructed as a place to direct the rain from your roof or driveway, and is landscaped with perennial plant species native to our region. Rain gardens have loose, absorbent soils; a shallow, bowl-shaped ponding area; and are made to resemble the function of a natural meadow or light forest ecosystem.

Why a Rain Garden?

A rain garden is a natural way for you to help solve our stormwater pollution problems, help recharge groundwater, and protect our water resources. A rain garden keeps rain on your property, where it naturally belongs. By creating a rain garden, you can help improve water quality in local streams, rivers, and lakes. You can use rain the way nature intended, instead of throwing this resource away.

In addition, rain gardens are attractive landscaping features. They use Michigan’s native species of plants that are adapted to our region, and can be low maintenance while providing habitat for native wildlife and butterflies.

Why is Stormwater a Problem?

We tend to think that large industrial polluters cause most water pollution, but this is not the case. We are the real culprits. Studies by the Environmental Protection Agency (EPA) have determined that up to 70% of the pollution in our surface waters is carried there by stormwater runoff. Some studies show that about 50% of such pollution comes from individuals and homeowners, due to yard care, yard waste, and chemical pollution from household activities.

But Rain is Natural and Clean, Isn’t It?

Rain is clean when we get it. It’s what we do to it afterward that causes the problems. When it rains, water runs off of our roofs, parking lots, streets, and lawns, instead of soaking into the soil the way it did before development. This water, along with everything it picks up along the way, ends up in storm sewers and ditches that discharge to streams, rivers and lakes. Salt from roads, pet waste, lawn nutrients, spilled gas, oil and other pollutants are all washed into the local waters.

In addition to carrying pollution, the stormwater runoff can be warm, causing a pulse of warmer water to flow down the stream. In a natural system, water enters a stream through a slow and steady release from groundwater. Groundwater has a fairly cool temperature, which allows water to hold more oxygen. Many sensitive creatures such as trout cannot survive in a stream with fluctuating and warmer temperatures

While groundwater release is slow and fairly steady, stormwater runoff occurs all at once. The large volumes of warm water flushing down a stream cause erosion and flooding, carry dam-forming debris, and scour the stream bed.

By creating a rain garden on your property, you can keep rain on your property where it naturally belongs. You can help be part of the solution to stormwater pollution. In addition, you gain a lovely garden.

Rain Garden History

How Did Rain Gardens Get Started?

Rain gardens, or bioretention systems, were first conceived of in 1990 by stormwater specialists in the state of Maryland. Since that time, a number of people, municipalities and organizations have influenced and enhanced the rain garden movement in the United States.

The First Rain Gardens

The first rain gardens were our native ecosystems. Before our lands were settled, rain was filtered through soils, roots, and plants in our native forests, wetlands, and meadows. Most of the water that entered our surface waters was cool, clean groundwater. Our wealth of streams, rivers and lakes was naturally clean.

When European settlers cleared the land and built communities, the natural water-cleaning systems were removed. Our streams and rivers became more and more degraded as water ran off the land instead of being taken up by plants, soaking into the soil, and filtered by soils and wetlands.

Rain gardens were invented as a way of imitating the function of these natural filtering systems that development removed. Infiltration was already in use, where stormwater is stored to soak into the ground. However, the introduction of plants to the system was a new idea for stormwater engineers.

Maryland Rain Gardens

Rain gardens and bioretention originated in Prince George’s County, Maryland. Larry Coffman, head of the county environmental programs, was investigating cost effective, lower maintenance methods to improve infiltration systems for septic systems and to improve water quality in stormwater handling installations. He and his team came up with the idea of bioretention, or holding and filtering stormwater in plant systems, and then coined the term “rain gardens” which is a term that most people find very attractive. Coffman told us, “Believe it or not -it took us about 2 hours to finally put rain and gardens together! This pioneering stuff is hard work!”

“I began to realize that we could use the functions of the upland ecosystem (plants, microbes and soils) to treat stormwater water runoff. One other factor influenced my thinking and that was the studies we were getting back on BMP’s (Best Management Practices) efficacy showed there were major problems with cost, maintenance and operations. So I got the idea of designing the green space in a parking lot to treat/infiltrate the runoff,” Coffman said.

After doing a literature review, they discovered there were no guidelines for using infiltration and bioretention. They had to develop all of the principles and design standards from scratch. They found it to be feasible based on how plant/soil filters technology had been successfully used in water treatment and wastewater treatment in the past. Since they were developing a practice that would be in an upland area they also brought in the sciences of forestry, soil science and agriculture. Transferring technology from all of the related fields of science they came up with the first bioretention design guidelines in 1993. The goal was to design bioretention to mimic forest or meadow functions.

In 1997 in cooperation with the University of Maryland, they began a monitoring program to test the pollutant removal of bioretention and optimize its design.

“Since then we have improved the design and learned about the whole new world of the complex and wonderful plant/soil/microbe ecosystem, andhow to use nature to protect nature and make things prettier too, ” Coffman told us.

The Bioretention Manual of Prince George’s County, Maryland, is available for download and is a wonderful resource.

Minnesota Rain Gardens

The City of Maplewood, Minnesota, working with designer Joan I. Nassauer, Professor of Landscape Architecture at the University of Michigan, created lovely formal homeowner rain gardens that set a new standard for attractiveness. This 1996 project took the rain garden movement even farther by making a rain garden, and stormwater management, part of an accepted formal landscape element for residences. Joan Nassaur’s professional skills, and interests in both landscape design and in watershed planning, resulted in lovely garden designs that are very well accepted in Maplewood. The project was funded in part by Legislative Commission on Minnesota Resources.

Michigan Rain Gardens

The Southeastern Oakland County Water Authority started a rain garden project in the Rouge River Watershed. A rain garden was installed in Lathrup Village in 2002.

Rain Gardens of West Michigan was established as one of the many water quality programs of West Michigan Environmental Action Council, Grand Rapids, Michigan, in the fall of 2002. For more information about our rain garden projects, please investigate this website.

The Kalamazoo Nature Center, in partnership with the Michigan Department of Environmental Quality and the Kalamazoo Watershed Project, installed a rain garden in the Axtell Creek Watershed in Kalamazoo. Engineering studies began in the summer of 2002.

Wisconsin rain gardens

The University of Wisconsin Extension and the Wisconsin Department of Natural Resources have an excellent rain garden program headed by Roger Bannerman, and published helpful documents and websites about their activities in 2002.

Qualities And Benefits

What Makes a Rain Garden a Rain Garden?

A rain garden resembles a regular perennial garden in many ways. It is designed with deep-rooted plants that come back year after year; it is pretty to look at; it often has lovely flowers, grasses, trees and shrubs. So what makes it different from any other perennial garden?

There are certain qualities that make a rain garden unique.

  • Rain Gardens have a ponding area, but they are not ponds. They often are planted with wetland plants, but they are not wetlands (although you can design a rain garden that mimics a wetland).
    The garden absorbs and filters rain that would otherwise run off your property and down the storm drain. This stormwater runoff usually comes from an impervious surface that rain cannot soak into, such as a roof or parking lot, or even a lawn.
  • Many of the plants in the garden are native to the region, and have extensive deep roots that help the garden absorb rain. The native plants do not need special attention once they are established.
  • There is a bowl-shaped dip in the garden, which holds the rain while it soaks into the soil.
  • The garden bed is prepared or sometimes replaced to a depth of two feet in order to de-compact the soils and make the garden able to absorb water.

A native plant garden that does not have rain directed into it from a hard surface of your property will still be a valuable asset, and will help absorb rain much better than a traditional landscape. But unless stormwater runoff is directed into the garden, it is not a rain garden.
Benefits of Rain Gardens

  • Rain gardens are lovely landscaping features.
  • Rain garden plants create wildlife habitat and attract butterflies, birds, and other wildlife.
  • Rain gardens can save you money. They don’t need to be fertilized or sprayed, only weeded and mulched. They reduce the amount of lawn you have to maintain. This makes your yard a healthier place for children and pets.
  • A rain garden on your property makes you part of a solution to stormwater pollution. Rain gardens can potentially absorb hundreds of gallons of rain that would otherwise wash pollution down the street and into the nearest river, stream, or lake. Even small rain gardens can absorb a lot of rain.
  • A rain garden can be part of a stormwater reduction plan to help solve problems of combined sewer overflows (CSOs).
  • Rain gardens can actually remove many of the common pollutants in stormwater.
  • Rain gardens are low maintence. Once established, they require no fertilizer, watering, or mowing. A once a year cleanup, addition of shredded hardwood mulch to keep the surface moist and tidy, and removal of weeds and invasive species are all that are required.
  • Rain gardens can contribute to groundwater recharge, a natural process that is interrupted by soil compaction and hard surfaces created during development and building.
  • A rain garden project can educate the public about the problems that stormwater runoff creates, while giving people a beautiful solution.
  • A rain garden project can be part of the educational toolbox used by a community stormwater education team.

As you can see, there are many benefits to using rain gardens. Explore the website to learn more. Put in a rain garden and enjoy these benefits yourself.

Create A Garden

Ready to Make a Rain Garden?

Welcome. We hope the tips and information in this section will be helpful to you in the process of creating a rain garden.

A “Perfect” Garden?”

First off, we will be describing an “ideal” rain garden. But of course, we recognize that perfection cannot always be achieved—your lot may be too small, contoured oddly or your soil may need major modifications to make a perfect rain garden.

The point is, any rain garden is better than no rain garden. For example, we’ll tell you how to calculate size so that your rain garden can probably handle 100% of the runoff from your property. But if you can’t make a garden that big, a rain garden that can handle any part of your rain runoff will still be a great contribution to restoring clean water in your neighborhood, your city, and your region. Similarly, we’ll recommend plants native to Michigan as being the most suitable, but if your budget is tight or the plants are not readily available, you may be able use some existing plants from your yard and add the superb native species later.

If you don’t have a rain garden, runoff from your rooftops, lawns, and driveways will continue, with rain and snow melt, contributing to water pollution rather than curing it, as nature intended. Every little bit that you can keep on your property helps!

Remember, rain gardens can be an integral part of our stormwater management and environmental approach. Their use doesn’t involve a lot of centralized planning. They don’t require much space, can be fitted into oddball shapes, and can readily added to existing buildings. They look nice, and you don’t need to be an engineer to build one. Anyone can make a rain garden — including you!

Before Starting

Choose The Right Place for Your Rain Garden

A rain garden is one type of “bioretention”—a system of pond area, soil, plants and mulch that will retain water and soak it up instead of letting it run off of your property (even though your “pond” will be dry most of the time). So the most basic things are the “pond,” or depression into which water will flow, and the soils that will absorb the water.

Your property has an existing drainage pattern (even though it may not be very noticeable), and it will usually be easiest to take advantage of that. Note the direction of runoff and low spots where water collects. If you are not sure where these are, and it’s not raining, find them by running hose water on the ground.

If these spots are away and downhill from your building foundations, they will be good places for your rain garden.If there is a spot on your property where standing water collects, this area has poor infiltration. You may think it is thus the wrong spot for your rain garden. However, if you could collect water anywhere on your property, these areas would likely have poor infiltration also. This is because soil is compacted during construction in order to prevent sinkholes and to support building foundations and other structures. This general compaction of building site soils makes the need for your rain garden even more critical.

If you have many low spots, you can choose those that are closest to the downspouts from your roof or nearest to a paved driveway.

If the layout of your land is such that you don’t like the natural low spots (or they are not very low), you can create your own by excavating earth—anywhere that you can get rainwater to flow, either directly or even by installing piping. For preparing large gardens or in very hard soil, it may be worth your while to hire an excavator to bring in a machine for a few hours. Have the excavator use the removed soil to create a knoll or other pleasing contour to your property. Be aware that driving any kind of heavy equipment on your land will compact the soil, and reduce its ability to absorb water.

If your land is sloped and all the water drains away, you can still build a rain garden by designing a level “scallop” or small terrace in your slope, and creating a rain garden there.

A few hints for choosing a spot:

Avoid creating a rain garden too close to building foundations; this may lead to a leaky basement. If you can locate it at least 10 feet and downslope from the building, that should be good. Also, you must stay away from the drainfield if you have a septic system. They don’t need any added water.

Be aware of rights of way and underground service lines or utilities. Avoid excavating or planting in these areas (this includes the drainage ditch in front of your house). You don’t want to accidentally dig up your phone line, and there may be restrictions to activities in rights of way. Before you dig, call “Miss Dig”, and have the area flagged. Hint: take pictures of the flagged areas so you have a record of underground utility locations.

Re-directing the rain–there are a number of creative and attractive solutions if the rain doesn’t flow naturally to your chosen spot. You can install piping underground or send the rain along a constructed channel or swale. Treat these as part of your landscaping—they can be beautiful additions. You can also incorporate a rain barrel into the feature, and direct the overflow hose into your rain garden (this way, you can save your rain for a sunny day!). We will feature examples in our demonstration site area.

If your land slopes, you can create a flat area for your rain garden in several ways. You can create a “weep” rain garden by building a small retaining wall and filling in behind it. The water will soak into the garden, filter through, and weep out the retaining wall. You can also dig out a “scallop” in the side of a hill for your rain garden.

Black walnut trees growing by the garden may spell trouble, due to juglone, a chemical exuded from their roots. Some plants are sensitive to juglone and will not grow well near walnut trees. If possible, locate your rain garden away from these trees. If you can’t, we have a list of juglone-resistant plants (Can’t read pdf files? Click here to download Adobe Acrobat Reader).

Don’t excavate an extensive rain garden under large trees. Trees have root systems that would have to be dug out in the excavation, and the health of the trees may be affected by damaging the roots. If the trees are not species that are adapted to rain garden conditions, directing ponds of water to their roots may also weaken or kill them. Trees enhance our communities and are very good at absorbing rain; protect them.

Evaluate the Soil

Soils vary greatly in fertility, drainage, and “pH” rating. It is best if you understand what kind of soils you are working with, and put in a garden suitable to the conditions you already have.

Drainage is important

Your rain garden needs to be able to absorb the water coming off your roof and driveway. In West Michigan, soils tend to be predominantly sand or clay. Sandy soils drain well, while clay soils may become waterlogged. If your soil is sandy, you may be able to simply loosen the soil and improve it with some compost to prepare your rain garden for planting. If your soil is clay, you will have more work to do. Even light clay soils may create very soggy problems if a lot of rain is directed to the rain garden. Soil removal and replacement are often needed if your soil is clay. The recommended soil replacement mix is 50-60% sand, 20-30% topsoil, and 20-30% compost. Be sure no clay is in your replacement soil.

Test your drainage!

You can test your soil’s infiltration rate by digging a hole 8 inches wide and 8 inches deep. Pour a bucket of water into it and see how long it takes to sink in. The water needs to go down an inch per hour. If it takes longer than that, you will need to do additional site preparation to improve infiltration.

Design the Pond Area

When you prepare the garden for planting, you must create a dip in the middle where water will collect as it sinks into the soil. There are various  zones in a rain garden (very wet, wet to dry, and dry) and different kinds of plants will thrive at different zones.

You may also adjust the depth of the depression to the infiltration rate. The standard depth for the ponding area is six inches. If you have very poor drainage in your existing soils, and your garden preparations still leave you with slow absorption rates, make your depression shallower to reduce the water that gets trapped there. If your soil sucks up water, make your garden deeper to increase its storage capacity. It’s generally best to keep the bottom of your rain garden’s depression flat; saucer-shaped rather than bowl shaped. That way, the rainwater will always spread out as much as possible.

To be certain that your rain garden will function properly, simply replace the soil with the recommended rain garden mix: 50-60% sand, 20-30% topsoil (no clay), and 20-30% compost. This mix allows water to soak in and supports the growth of healthy plants.

Drain Systems

If the soil is very heavy and/or a lot of water will need to be infiltrated, an under-drain system of gravel and perforated pipe (French drain) may be helpful. This will enable the garden to absorb more rain. Sometimes a rain garden is constructed to absorb and filter a certain amount of rain, and the filtered water is then piped to another location through the underdrain system.

Compacted Soils

Soils on developed land have been compacted by heavy construction equipment. Packing soil down is actually part of the construction site plan, to avoid the formation of sinkholes and to stablize building foundations. Even sandy soils are often much reduced in their capacity to absorb rain after trucks and bulldozers have run over them. To make a properly functioning rain garden, these soils will need to be dug up and loosened to a depth of two feet, not only to prepare for planting the garden but so rain can soak in. If you have extra soil left over after this loosening process, use it in another part of your yard.

pH and Other Qualities

Uncertain about kind of soil you have? To know how to prepare your rain garden and which plants will work best in your situation, you should have your soil tested. In Michigan, this can be done for a small fee by your local Michigan State University Extension office. They will also advise you on how to improve your soils. In Grand Rapids, call 616-336-3265 for soil testing information and fees. Other offices can be found here: Michigan State University Extension Directory.

Develop a Design

Even if you choose one of the standard designs that our gifted gardeners have donated, every garden on earth is site specific. The rain garden you have in mind may be a different size or shape than the design provided, or you may want take things out, add things, or design your own. No matter what you choose to do, you must adapt your garden to the local conditions of your site.

Regarding size

You can’t have a rain garden that is too large. However, any size garden will make a difference, even a small one. The ideal situation is to create a garden that will absorb all the rain that would otherwise flow away from your yard. To calculate the most useful size of a smaller garden, here’s how:

  • Figure out what kind of soil you have.
  • Estimate the area from which your garden will get rain. Multiply width times length of your rooftoop, to get square feet. Add the square feet of paved areas. Remember, though, that different parts of your roof drain to different downspouts—you want to estimate only the square footage that will drain into your rain garden. Don’t forget roof overhangs.
  • For sandy soil, your rain garden should be 20-30% of the drain area. For example, if your roof and driveway measures 1200 square feet and all the rain from them will be used, your rain garden should be 20 to 30% of that, or 240-360 square feet. (ex: 10’ X 24’)
    For clay soil, your rain garden should be about 60% of the drain area (Clay absorbs water very poorly; the varieties of rain garden plants that do well in clay take at least three years to get established. Soil replacement may be the best choice in clay soils).
  • If you improve your soil drainage and replace your soil with rain garden mix (50-60% sand, 20-30% topsoil, 20-30% compost), your rain garden should generally be about 20-30% of the square footage of your drain area.

Rain gardens for single-family homes will typically range from 150 to 400 square feet. But remember; any size rain garden, even a small one, will contribute to solving local water pollution problems. It will also be a lovely addition to your landscape.

Prepare the Site

Sometimes creating a rain garden is as simple as directing rain to an absorbant swale in your yard and perhaps putting in a few plants. If you have no convenient place to direct your roof runoff, or you want a formal garden design, then it’s time to get down and dirty.

Soils on developed land have been compacted by heavy construction equipment. The soils will need to be dug up and loosened to a depth of two feet, or replaced with rain garden soil mix (50-60% sand, 20-30% topsoil, 20-30% compost), not only to prepare for planting the garden but so rain can soak in. If you have extra soil left over after this loosening process, use it in another part of your yard.

Preparing a rain garden is just as much work as creating any other perennial garden. Get out your shovel and dig to produce beautiful results.

Define the Borders

First, define the borders and shape of your garden at the location you have selected. When we prepare a rain garden, we outline the area to be dug by spraying with non-toxic soccer-field paint. Another method is to lay a hose along the shape of the garden, then dig along the hose. This gives a nice flowing border to the garden area. Or, you could simply choose a rectangle as the shape of your garden.If the area is lawn, you will have to remove the turf. You can either use this either in another area of your yard, or it can be composted to help improve your soils. There is a special tool for removing turf that can make this task easier.

If you are not replacing your soil, double-digging to a depth of two feet is recommended. Remove the soil from the hole and pile it to the side; then dig and loosen the earth in a new hole, and pile it loosely into the first hole. This is the time to mix compost into the soil, if you are doing soil improvements. Continue until the whole garden is prepared. A great tool for this purpose is a digging fork. Try it, you’ll like it!

To be certain that your rain garden will function properly, simply replace the soil with the recommended rain garden mix: 50-60% sand, 20-30% topsoil (no clay), and 20-30% compost. This will give your new plants a great start, and the soil mix is designed to soak up rain.

If your site soils are clay, soil replacement is probably in order. You may also want to add a reservoir of gravel at the bottom of the garden bed, or add tiles or an underdrain that leads to another area. This will avoid having your rain garden become waterlogged. The idea is to create a living sponge of soil, plants, roots and mulch, not a soggy bog.

How much soil is needed for replacement?1 cubic yard=27 cubic feet.

A rain garden that is 2 feet deep X 5 feet wide X 10 feet long will need 100 cubic feet of replacement soil, or about 3.7 cubic yards.

Improve the Soil

In most of West Michigan, adding compost or other organic matter is the best way to enrich your soil. A compost of decomposed yard waste such as dead leaves and grass clippings is generally the best bet (this is another resource that shouldn’t be wasted!). If you do not have your own compost, compost can also be purchased at garden centers and many other retail locations.

Grading the pond area

Grade the surface of your prepared rain garden bed in such a way that the water entering it can spread out over a large flat area and soak into the soil. This may involve removing a lot of soil.

The depth of the dip should be about six inches. The depth can be graduated from the edges of the garden to the middle. This avoids creating a crater that people can trip and fall into.

When your pond area is ready and the soil is nice and loose, it’s time to plant. You can prepare a rain garden bed and then cover it with mulch until later; then, plant through the mulch. Or, you can plant immediately, then mulch the plants. The choice is yours. The sooner the plants are in, the faster your rain garden will get established.

Select the Plants

Why use native plants in rain gardens?

We recommend using native plants in your rain garden for a number of reasons. Our garden designs are a combination of native species and of non-native plants (for example, daylilies do very well in rain gardens). Although many non-natives also do well, there are some unique benefits to using natives that you should consider.

Native plants can tough it out

Plants that are native to your area are uniquely adapted to thriving in the local weather, soils, and ecosystems. They have been working at it for years (thousands, in fact). They live through droughts and downpours, and survive the winters without special care. Fertilizer will make them grow bigger, but they grow beautifully without it. Pests munch on them and the plants bounce right back without chemical pesticide sprays. Just think of the reduced chemical load in your yard! Much healthier for you, children and pets.

Native plants attract beautiful creatures

Native plants also have relationships with local butterflies, insects, birds, animals and other plants that they have developed by living together over thousands of years. Planting natives in your landscape helps provide habitat for local wildlife. How long has it been since your yard was decorated by butterflies and birds?

Native plants have deep roots

Native plants are great helpers for protecting water quality in your neighborhood. The deep roots of many established native plants increase the ability of soil to hold water. For example, Blue False Indigo, Baptisia australis, grows only 3-5 feet tall, but the roots may go down 25 feet! These fantastic roots create deep channels in the soil for rain to soak into. Some of the roots die each year, and new roots grow. The decomposing roots enrich soil, making it more fertile and absorbant. The root systems also hold soil together and help prevent erosion.

Where can native plants be obtained?

Many of the native plants that do well in rain gardens are not available from traditional plant nurseries and retailers. One must instead contact certified, inspected professional nurseries that specialize in native species, such as the Michigan Native Plant Producers Association.

Wherever you get them, verify that the native plants you purchase are not collected from the wild, reducing local populations, but are instead produced in a sustainable way by the nursery.

Please do not take your plants from the wild. Doing so disturbs local plant ecosystems and is often illegal. The plants you want may indeed now “grow everywhere”, but they soon won’t be if people start removing them from native populations.

If there is a local Wild Ones chapter, or a nearby garden club, they often hold plant exchanges or sales. Plant rescue is another option; get permission to remove plants from a site where construction will soon destroy them and their habitat. Or, if you want to wait that long, you can grow plants from seed.

We are currently updating a downloadable list of retail and wholesale sources for native plants and seeds, for Michigan and surrounding regions. This list is not an endorsement of these suppliers, but is merely listed for your convenience. It is important that anyone purchasing from any of these suppliers understand that it is their own responsibility to ensure that they are getting a reliable and quality product.

Plan Ahead for Plant Needs

Timing is extremely important in obtaining plants for your rain garden or bioretention project. It is not possible for suppliers to keep an extensive inventory of native plants and seeds on hand. In fact, some native plant producers only have plants on hand that have been pre-ordered. Growers try to anticipate needs for native plants and seeds, but it is not economically practical for them to grow plants they do not have a ready market for. Many of them grow plants to order, but it can take several years to grow plant material or collect seed for a specific project. This is even more complicated if you are seeking plants or seeds from a specific region, if you want to use local genomes for your project. Keep this in mind when you are searching for particular plants or large quantities of plants.

One solution to the plant availability problem is to start your own native plant nursery to provide for your own project needs. This does take time, effort and money to establish, but is well worth the effort if your needs will last for several years.

We wish you good fortune in your plant-seeking ventures.

Plant the Garden

If you improve the soil before planting, your plants will have a healthy start.

Native Plants for Rain Gardens

We recommend our beautiful native species for rain gardens, or a combination of cultivated varieties and natives. The advantage of using natives is that they will thrive with little care, once established.

Although native plants species are low maintenance, that doesn’t mean NO maintenance. Designing the garden for easy maintenance is part of your planning process. If you use or adapt existing garden site plans, keep the following guidelines in mind:

Put the right plant in the right place. Choose plants or a design suited to the existing conditions of the site. For example; if a garden is in deep shade then plants that require sun are not going to thrive. Some plants are adaptable as to soils, and some are not. Choose with the needs of the plants in mind.

If a plant is not happy, move it. Rain gardens also have three zones; very wet, wet-to-dry, and dry areas at the edges. Our rain garden plant database will let you identify which zone each plant does best in, but you will have to evaluate your own garden to see where in your garden the plants you select will thrive. If a plant is not doing well in one location of the garden, it’s a good idea to move it. Sometimes the wettest areas are not where you thought they would be!

If you use a design with tall plants, think about how this will affect the view. Some prairie plants can grow ten feet tall. This could be a good thing, or it could inconveniently block the view of street traffic from your driveway.

Mulch makes things easier. Plan to mulch your rain garden, which will keep it moist, protect your plants, discourage weeds, and make weeds easy to remove. How much mulch? A cubic yard of mulch will cover approximately 100 square feet 3″ deep. A 10 X 20 (200 square feet) rain garden will require 2 cubic yards of mulch.

A rain garden is a GARDEN. Remember that a rain garden is not merely a functioning infiltration system. Rain gardens can and should be beautiful—an attractive improvement to your property. Choose your plantings to delight, and arrange them so that they are pleasing to your eye.

Rain gardens also tend to become wildlife oases—you can expect and should plan for songbirds, butterflies, colors, fragrances, and sounds. And—depending on your neighborhood—you may have squirrels, rabbits, or deer visiting y

Natives will grow bigger with fertilizers, but don’t require them. They won’t require spraying with pesticides. Just think of the reduced chemical load in your yard! Much healthier for you, children and pets.

Native Michigan species may be available at some local plant retailers, but usually have to be purchased from native plant nurseries. See the navigation or site map for an introduction to our native plants, and information about where to purchase them in our area.

Big Pots Mean Deep Roots

Choose plants that have healthy root systems. Larger plants are more costly, but the bigger pot size allows for more roots. Those roots are very important, as the healthier the root system, the sooner the plants will be established.

If you plant in the fall, some of your plants may be dormant. Do not throw these dormant plants away! They are still alive in their pots, and will sprout up from those healthy, deep, perennial root systems in the spring to dress up your rain garden in a fine fashion.

Planting Day!

Our garden designs are on a grid, which can be transferred to your garden site. We lay out the grid with string or soccer-field marking paint. Then we place the plants, in their pots, at the location on the grid where they are to be planted. If we are working with volunteers, we then instruct them on how to plant.

Plants must be removed from their pots before planting (some people really do need to be told this). Don’t pull them out by the stems, or you may damage the plant. Instead, loosen the root ball, then slide the plant gently out of the pot. Break the root ball up slightly, and place the plant in the soil at the same level it was growing in the pot. Generally, it is a good idea to demonstrate this a couple of times before turning your volunteers loose in the garden.

Once the plants are in, give them a good watering to get them settled into their new home.

Once the plants are in, the mulch is applied. A shredded hardwood mulch is best, as it breaks down more slowly and clings to itself and to the soil. Be sure the crowns of the plants are free of mulch.

If there is a specific spot where rain is flowing into your garden, you will have to break up the flow with a few strategically placed rocks. Otherwise the force of the rain entering the garden will cause erosion. This, too can be part of your attractive design.

Now your rain garden is complete

Rain Garden Care

Rain gardens are low maintenance, but not NO maintenance. You worked hard to create your rain garden, and to keep it working well for you and looking its best, some regular care is required.

If it doesn’t rain, water your plants until they are established.

Once the deep root system has grown into the soil, they will probably survive a drought. But until then, just like any newly planted perennials, they need water to get started. (Hint–use water from your rain barrel!).

Break strong water flow.

The area where water flows into your garden can, during frog-strangling thunder storms, erode soil, mulch, and plants (think of the Grand Canyon–water can do a lot of work). A few strategically placed rocks, boulders, or stone dams in this area of strong water flow can break the force and prevent this from happening.

Mulch your rain garden.

If you have a formal rain garden, 3 inches of shredded hardwood mulch should be applied in the spring after the plants break dormancy, or if bare areas appear, more often (note: take care not to bury plant crowns. Some plants are dormant until late spring and mulch may cause the plant to rot and die). Chipped bark mulch can also be used, but tends to float. Mulch keeps the garden moist and spongelike, ready to absorb rain. It prevents a hardpan from developing on the surface of the garden. Mulch protects the plants in the garden as they get established and makes it easier to weed. It also gives your garden a formal appearance that many people find very attractive.

Weed regularly.

A nicely prepared rain garden is a great place for invasive plants to start growing. Siberian elms, honeysuckle, mulberry seedlings, garlic mustard, and the dreaded purple loosestrife will all take advantage of that nice loose soil you have worked so hard on. This is where mulch comes in handy; it will be simple to just pull those little seedlings out before they get established (If you have trouble identifying weeds, check out the NPS.Gov alien plant site for assistance).

Don’t park or drive on your rain garden.

Just like a septic field, it needs to be protected from getting squashed. Otherwise, it will not be able to absorb your rain!

Don’t let sediment, soil, sand, or debris flow into your rain garden.

It can bury the plants, destroy the absorbancy, and ruin all your efforts.

Keep an eye on the plants. If a plant isn’t thriving where you placed it, don’t be shy about moving it to another location in the rain garden. A rain garden has different zones of wet, wet to dry, and drier areas, and sometimes it isn’t easy to tell exactly where a particular plant will grow best until it has rained a few times. A rain garden is a living system; go with the flow.

Enjoy your rain garden! If you install a rain garden in the West Michigan area, we would like to hear about it. Please let us know!

References for the Create A Garden section:

L. S. Coffman and D. A. Winogradoff, 2001, 2002. Prince George’s County Bioretention Manual. Program and Planning Division, Dept. of Environmental Resources, Prince George’s County, Maryland.

Maplewood, Minnesota Department of Public Works, Engineering Division, 2003. Rainwater gardens.

B. Damrosch, 1988. The Garden Primer. Workman Publishing Company, NY NY.

Ladybird Johnson Wildflower Center, 2002, 2003.

Wild Ones, 2003. Native Plants, Natural Landscapes.

our garden regularly.

, and a celebration is in order!

Choosing your plants

We recommend native plant species, since they are naturally adapted to the wet and dry cycles and seasons of Michigan weather and will generally require the least maintenance.

1 Komentar »

  1. translate into indonesian

    Komentar oleh Anonim — Februari 24, 2011 @ 2:53 pm

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