Miscellaneous

Rain Garden Design, Benefits, and Plants

Rain Garden Design, Benefits, and Plants


WHAT IS A RAIN GARDEN?

A rain garden is a shallow planted depression designed to hold water until it soaks into the soil. A key feature of eco-friendly landscape design, rain gardens—also known as bio-infiltration basins—are gaining credibility and converts as an important solution to stormwater runoff and pollution. Here we’ll show you how to make a rain garden fit handsomely into a landscape and still fulfill all of its environmental functions.

Naturalized plantings, here camassia, can make a rain garden fit easily into its surroundings. Photo by: Rob Cardillo.

According to the EPA, much of the rain that falls on a typical city block heads overland to the nearest pipe, washing along any crud it finds. Historically that water would have infiltrated—soaked in—leaving impurities behind in the soil and plants as it passed through to replenish the water table. Rain gardens are intended to counteract both the unnatural runoff patterns in urban and suburban areas (too many roads, too much paving, too many hard surfaces) as well as the increased crud levels found in them.

Rain gardens can work in most climates, but are most effective in regions with a natural groundwater hydrology—that is, areas with deep soils that drink in water rather than rocky areas that force rain to run overland. Most of the United States is like this. Rain gardens have gained wide residential use in cities as diverse as Kansas City, Minneapolis, and Portland, Oregon (the latter two offer utility-bill discounts for rain-garden installation). Entire towns, such as Maplewood, Minnesota, have turned to rain gardens to handle neighborhood storm-water management, plunking little planted basins down between curbs and property lines.

Swaths of pennisetum and other grasses convert a large, shallow-draining swale into a textural garden. Photo by: Rob Cardillo.

More than a dozen rain-garden designs can easily be found on the Internet. Essentially, you dig a basin, plant some water-tolerant plants, mulch it in well, and redirect your downspouts to the hole. The online guides will tell you to locate a rain garden 10 feet from your house and at a natural low spot. That’s a good start, but your rain garden runs the risk of just floating out there, awash in lawn and disconnected from your bigger design picture.

RAIN GARDEN DESIGN TIPS

  • Think of a rain garden just like a border or foundation planting rather than a beloved specimen tree. In other words, it should not be a stand-alone feature.
  • Consider all the rules of composition, screening and circulation—not just the rule that says to put a rain garden in a low spot 10 feet from the house.
  • Pick a shape that works with the rest of your garden design. A rain garden does not need a specific shape to function properly so feel free to be creative.
  • A rain garden can be as formal or as wild as you like—it’s all about the plant selection. Monocultural rain gardens are okay as long as that fits with your overall design. (See below for some of our favorite rain garden plants.)
  • A rain garden doesn’t have to be separate from other plantings. Consider making a depression within a perennial bed or shrub border (especially if space is tight and you don’t have room for a larger rain garden that stands alone).
  • Put in more than one rain garden for repetition and continuity. If it works with your overall design, create a little rain garden for each downspout.

Biostream at Scott Arboretum, Swarthmore College, collects excess rainwater, slowly filtering and releasing it into the landscape. Planted with amsonia and Iris pseudacorus, which tolerate periodic flooding. Photo by: Rob Cardillo.

“So how can we get away from a rain garden being a kidney shape plopped in the front yard?” asks John Gishnock III. My thoughts exactly, because that result is pretty common. Gishnock is owner of Formecology, a design/build firm specializing in rain gardens and native plants in Wisconsin. He has created rain gardens that are seamlessly incorporated along typical suburban driveway-to-door sidewalks; gardens below dry-laid stone walls adjacent to rustic pathways; and even a garden in the shape of a spiral galaxy (to be viewed from a lucky owner’s second-story porch). “A rain garden,” says Gishnock, “needs to look like the rest of the landscape.”

Landscape architect Jim Hagstrom of Savanna Designs in Lake Elmo, Minnesota, agrees. “We integrate rain gardens into the design,” he says, “and two-thirds of the time you won’t notice them.” His designs depend mostly on his clients’ sensibilities. Some love the wild native look of a traditional rain garden, while others favor the idea of infiltration but don’t want to see a “patch of weeds.” He has incorporated a rain garden into the center of a circle drive and devised a standing stone flow-through curb to match the house. He has created a large basin that infiltrates most water then holds the rest for pond habitat. He has built rain gardens in the centers of lawns, by dishing the landscape and ensuring well-draining soil. “You get a little pond after a rain,” he describes, “and in 24 hours it’s gone, and you have the lawn back.”

Flowers of hot-pink primroses punctuate a streamside garden at Chanticleer, bringing a pop of color to the varied greens of other moisture-loving plants, such as hostas, iris, ferns, and dwarf scouring rush. Photo by: Rob Cardillo.

However they look, rain gardens work, helping to reduce storm-water waste by 99 percent, according to one study, and keeping runoff clean. But they can also be an integrated design element, making landscapes both sustainable and beautiful.

RAIN GARDEN PLANTS

Plant selection for a rain garden can be a challenge. In addition to the favorite plants mentioned above, landscape architect Jonathan Alderson used these plants, among others, in a rain garden designed to solve drainage issues for a home being built in Wayne, PA. "The garden is the reason the house could be built," states Alderson, referring to the dilemma that no building permits could be issued until there was a solution for the poor drainage.

Swipe to view slides

Photo by: Rob Cardillo.

Orange coneflower
Rudbeckia fulgida
Zones 3-9

With regular deadheading, orange coneflower will bloom from summer until frost with orange-yellow flowers on stems that reach 3 feet tall.

Learn more about growing coneflower plants.

Photo by: Rob Cardillo.

'Northwind' switchgrass
Panicum virgatum 'Northwind'
Zones 5-9

Switchgrass grows 4 to 6 feet tall, so it’s good for screening less-than-desirable views. It spreads slowly by rhizomes.

Photo by: Rob Cardillo.

Obedient plant
Physostegia virginiana
Zones 3-9

This light purple bloomer grows 3 to 4 feet tall. Hummingbirds like it, but deer do not. Obedient plant blooms from early summer to early fall and spreads by both seed and rhizomes.

Photo by: Rob Cardillo.

Wild bergamot
Monarda fistulosa
Zones 4-9

Wild bergamot is an herbaceous perennial that brings hummingbirds and butterflies to the garden. It’s light purple-pink blooms last from late June through the beginning of August.

Photo by: Rob Cardillo.

'Aurantiaca' common winterberry
Ilex verticulata 'Aurantiaca'
Zones 3-9

Most winterberries have red fruits, but ‘Aurantiaca’ produces orange-red fruits that fade to orange-yellow in autumn. It is dioecious, which means it needs a male plant in order for the female to produce berries. ‘Aurantiaca’ grows to 5 feet tall in full sun to part shade.

Photo by: Rob Cardillo.

Northern sea oats
Chasmanthium latifolium
Zones 3-8

The seed heads of northern sea oats are attractive and look good in arrangements. Here, they mingle with bright yellow Amsonia hubrichtii.

May seed aggressively in some situations.

Photo by: Rob Cardillo.

Blue cardinal flower
Lobelia siphilitica
Zones 4-9

Blue cardinal flower grows to 3 feet tall, and vivid blue flowers appear from midsummer into early fall. In open conditions with moist soils, it will self-seed.

Photo by: Rob Cardillo.

Bluestar
Amsonia hubrichtii
Zones 5-8

Bluestar has two seasons of color: spring, when it produces periwinkle blue flowers on 2- to 3-foot stems; and fall, when the foliage turns brilliant yellow. Plant it in multiples for the best effect.

Photo by: Rob Cardillo.

'Fireworks' goldenrod
Solidago rugosa 'Fireworks'
Zones 4-8

Landscape architect, Jonathan Alderson refers to ‘Fireworks’ as a “well-behaved” goldenrod, because this cultivar’s rhizomes spread more slowly than the rhizomes of other species. Rough goldenrod’s golden yellow, gracefully arching panicles bloom from September into October, providing ample nectar for bees and butterflies. ‘Fireworks’ grows to 3 feet tall.

Learn more about growing goldenrod plants.

Additional rain garden plants include:

  • Blue flag iris (Iris versicolor or I. virginica)
  • Culver's root (Veronicastrum virginicum)
  • Fox sedge (Carex vulpinoidea)
  • Red twig dogwood (Cornus sericea)
  • Sweet flag (Acorus gramineus)
  • Lady fern (Athyrium filix-femina)

Portions of this article were contributed by Therese Ciesinski


Sustainable Landscapes: Designing a Rain Garden for Residential Property

We all know traditional gardens can add beauty and aesthetic value to property. Rain gardens not only add visual beauty to the landscape, but they also provide significant environmental value by reducing rainwater runoff, mitigating flooding and improving water quality. Unlike conventional gardens that typically sit even or slightly higher than the adjacent landscapes, rain gardens are situated lower than their surrounding areas and serve as a basin for capturing, holding and filtering rainwater after a rainfall event.


Rain Garden Design

Do your part to save natural water resources by planting a rain garden. Learn about this easy-to-grow, clever concept.

Related To:

We call this our Waterway. Rain water comes down our hill and runs to the side yard.

We call this our "The Waterway". Rain water comes down our hill and runs through cement/rock pathway to the side yard.

Do your part to minimize stormwater runoff by learning about rain garden designs. These clever, simple gardens help mitigate runoff while adding a beauty spot to your property. A rain garden is easy to build, and it more than pays for itself if your city imposes stormwater runoff surcharges to property owners. Discover ideas for rain garden designs.

In many cities, heavy rainfall in a short time combines with the hard surfaces of suburbia to swamp storm sewer systems. When this occurs, sewer systems can dump stormwater runoff, which carries road and lawn chemicals, pet waste, and fertilizers, into natural waterways. The result can be algal blooms, fish kill, and ongoing pollution.

In an effort to fund upgrading and improving storm sewer systems, some cities now charge homeowners for stormwater runoff. That fee can often be waived if you demonstrate that your property is an environmentally friendly rainscape that catches, contains or slows down stormwater runoff. This is where rain garden designs enter the scene.

By adding a rain garden, you can deal with stormwater runoff and improve your property value with an attractive landscape. Most rain garden designs comprise a simple saucer-shaped depression filled with plants. The depression slows stormwater runoff, catching, cooling and absorbing it into the earth. The soil and root systems of plants in the rain garden filter the runoff, cleansing it from pollutants. Because the rain water ultimately soaks into soil, it helps recharge local ground water supplies.

Properly installed rain garden designs shouldn’t create boggy areas that hold water for more than a day, so there’s no concern that mosquitoes can breed. Many professionally installed rain garden designs feature a sand or gravel drainage zone beneath the garden soil, but you can build your own rain garden simply by removing turf and digging shallowly.

A rain garden is typically a few yards across. Size really depends on soil type and how much space you have. An average rain garden size for a single family home varies from 150 to 400 square feet. The depression of the rain garden should create a 6-inch drop from surrounding grade. Excavate the sides of the bowl so they slope gradually, and level the bottom of the garden. Aim to create more of a saucer shape than a bowl.

The best place to locate a rain garden is down-slope, at least 10 feet away from your home’s foundation. Try to place it where water naturally runs off from your house, driveway, or other hard surfaces. Areas near downspouts are a logical choice for hosting a rain garden design. If you have a low spot in your yard that typically collects water from your property, that’s also a great place to site a rain garden.

Your rain garden can stand alone as a pretty planting area, or you may want to incorporate it into a swale or dry creek. If you plan to channel and direct water on your property, it’s wise to consult with a landscaper to make sure you’re not overlooking or even creating potential problems.

It may seem counter-intuitive, but you want to choose plants that withstand both wet soil and drought for your rain garden design. This is because at times the garden will have very wet soil, but at other times plantings will be swamped by rain water.

Choose a mix of native and ornamental plants for their rain garden. Good choices include turtlehead (Chelone glabra), switchgrass (Panicum virgatum), dense blazing star (Liatris spicata), purple coneflower (Echinacea purpurea), cardinal flower (Lobelia cardinalis ) and tall white beardtongue (Penstemon digitalis).


Contents

  • 1 History
  • 2 Urban runoff mitigation
    • 2.1 Effects of urban runoff
    • 2.2 Stormwater management systems
  • 3 Bioretention
    • 3.1 Water treatment process
  • 4 Design
    • 4.1 Soil and drainage
    • 4.2 Vegetation
    • 4.3 Pollutant Removal
  • 5 Projects
    • 5.1 Australia
    • 5.2 United Kingdom
    • 5.3 United States
    • 5.4 China
  • 6 See also
  • 7 References
  • 8 Further reading
  • 9 External links

The first rain gardens were created to mimic the natural water retention areas that developed before urbanization occurred. 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, an environmental engineer and the county's Associate Director for Programs and Planning in the Department of Environmental Resources, with the idea. [6] The result was the extensive use of rain gardens in Somerset, a residential subdivision which has a 300–400 sq ft (28–37 m 2 ) rain garden on each house's property. [7] 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. [6] This was also much more cost effective than building BMP ponds that could handle 2-, 10-, and 100-year storm events. [6] 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. [7]

Some de facto rain gardens predate their recognition by professionals as a significant LID (Low Impact Development) tool. Any shallow garden depression implemented to capture and filter rain water within the garden so as to avoid draining water offsite is at conception a rain garden—particularly if vegetation is planted and maintained with recognition of its role in this function. Vegetated roadside swales, now promoted as “bioswales”, remain the conventional runoff drainage system in many parts of the world from long before extensive networks of concrete sewers became the conventional engineering practice in the industrialized world. What is 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 developed communities retrofitting bioretention into existing stormwater management infrastructure as it is for developing communities seeking a faster and more sustainable development path.

Effects of urban runoff Edit

In developed urban areas, naturally occurring depressions where storm water would pool are typically covered by impermeable surfaces, such as asphalt, pavement, or concrete, and are leveled for automobile use. Stormwater is directed into storm drains which may cause overflows of combined sewer systems or pollution, erosion, or flooding of waterways receiving the storm water runoff. [8] [9] [10] Redirected stormwater is often warmer than the groundwater normally feeding a stream, and has been linked to upset in some aquatic ecosystems primarily through the reduction of dissolved oxygen (DO). Stormwater runoff is also a source of a wide variety of pollutants washed off hard or compacted surfaces during rain events. These pollutants may include volatile organic compounds, pesticides, herbicides, hydrocarbons and trace metals. [11]

Stormwater management systems Edit

Stormwater management occurs on a watershed scale to prevent downstream impacts on urban water quality. [12] A watershed is maintained through the cyclical accumulation, storage, and flow of groundwater. [2] Naturally occurring watersheds are damaged when they are sealed by an impervious surface, which diverts pollutant-carrying stormwater runoff into streams. Urban watersheds are affected by greater quantities of pollutants due to the consequences of anthropogenic activities within urban environments. [13] Rainfall on impermeable surfaces accumulates surface runoff containing oil, bacteria, and sediment that eventually makes its way to streams and groundwater. [2] Stormwater control strategies such as infiltration gardens treat contaminated surface runoff and return processed water to the underlying soil, helping to restore the watershed system. The effectiveness of stormwater control systems is measured by the reduction of the amount of rainfall that becomes runoff (retention), and the lag time (rate of depletion) of the runoff. [14] Even rain gardens with small capacities for daily infiltration can create a positive cumulative impact on mitigating urban runoff. Increasing the number of permeable surfaces by designing rain gardens reduces the amount of polluted stormwater that reaches natural bodies of water and recharges groundwater at a higher rate. [15] Additionally, adding a rain garden to a site that experiences excessive rainwater runoff mitigates the water quantity load on public stormwater systems.

The bioretention approach to water treatment, and specifically rain gardens in this context, is two-fold: to utilize the natural processes within landscapes and soils to transport, store, and filter stormwater before it becomes runoff, and to reduce the overall amount of impervious surface covering the ground that allow for contaminated urban runoff. [16] Rain gardens perform most effectively when they interact with the greater system of stormwater control. This integrated approach to water treatment is called the "stormwater chain", which consists of all associated techniques to prevent surface run-off, retain run-off for infiltration or evaporation, detain run-off and release it at a predetermined rate, and convey rainfall from where it lands to detention or retention facilities. [16] Rain gardens have many reverberating effects on the greater hydrological system. In a bioretention system such as a rain garden, water filters through layers of soil and vegetation media, which treat the water before it enters the groundwater system or an underdrain. Any remaining runoff from a rain garden will have a lower temperature than runoff from an impervious surface, which reduces the thermal shock on receiving bodies of water. Additionally, increasing the amount of permeable surfaces by designing urban rain gardens reduces the amount of polluted stormwater that reaches natural bodies of water and recharges groundwater at a higher rate. [17]

The concept of LID (low-impact design) for stormwater management is based on bioretention: a landscape and water design practice that utilizes the chemical, biological, and physical properties of soils, microorganisms, and plants to control the quality and quantity of water flow within a site. [16] Bioretention facilities are primarily designed for water management, and can treat urban runoff, stormwater, groundwater, and in special cases, wastewater. Carefully designed constructed wetlands are necessary for the bioretention of sewage water or grey water, which have greater effects on human health than the implications of treating urban runoff and rainfall. Environmental benefits of bioretention sites include increased wildlife diversity and habitat production and minimized energy use and pollution. Prioritizing water management through natural bioretention sites eliminates the possibility of covering the land with impermeable surfaces.

Water treatment process Edit

Bioretention controls the stormwater quantity through interception, infiltration, evaporation, and transpiration. [16] First, rainfall is captured by plant tissue (leaves and stems) and in the soil micropores. Then, water performs infiltration - the downward movement of water through soil - and is stored in the soil until the substrate reaches its moisture capacity, when it begins to pool at the top of the bioretention feature. The pooled water and water from plant and soil surfaces is then evaporated into the atmosphere. Optimal design of bioretention sites aim for shallow pooled water to reach a higher rate of evaporation. Water also evaporates through the leaves of the plants in the feature and back to the atmosphere, which is a process known as evapotranspiration.

Bioretention controls the stormwater quality through settling, filtration, assimilation, adsorption, degradation, and decomposition. [16] When water pools on top of a bioretention feature, suspended solids and large particles will settle out. Dust particles, soil particles, and other small debris are filtered out of the water as it moves downward through the soil and interspersed plant roots. Plants take up some of the nutrients for use in their growth processes, or for mineral storage. Dissolved chemical substances from the water also bind to the surfaces of plant roots, soil particles, and other organic matter in the substrate and are rendered ineffective. Soil microorganisms break down remaining chemicals and small organic matter and effectively decompose the pollutants into a saturated soil matter.

Even though natural water purification is based on the design of planted areas, the key components of bioremediation are the soil quality and microorganism activity. These features are supported by plants, which create secondary pore space to increase soil permeability, prevent soil compaction through complex root structure growth, provide habitats for the microorganisms on the surfaces of their roots, and transport oxygen to the soil.

Stormwater garden design encompasses a wide range of features based on the principles of bioretention. These facilities are then organized into a sequence and incorporated into the landscape in the order that rainfall moves from buildings and permeable surfaces to gardens, and eventually, to bodies of water. A rain garden requires an area where water can collect and infiltrate, and plants can maintain infiltration rates, diverse microorganism communities, and water storage capacity. Because infiltration systems manage storm water quantity by reducing storm water runoff volumes and peak flows, rain garden design must begin with a site analysis and assessment of the rainfall loads on the proposed bioretention system. [13] This will lead to different knowledge about each site, which will affect the choice of plantings and substrate systems. At a minimum, rain gardens should be designed for the peak runoff rate during the most severe expected storm. The load applied on the system will then determine the optimal design flow rate. [15]

Existing gardens can be adapted to perform like rain gardens by adjusting the landscape so that downspouts and paved surfaces drain into existing planting areas. Even though existing gardens have loose soil and well-established plants, they may need to be augmented in size and/or with additional, diverse plantings to support a higher infiltration capacity. Also, many plants do not tolerate saturated roots for long and will not be able to handle the increased flow of water. Rain garden plant species should be selected to match the site conditions after the required location and storage capacity of the bioretention area are determined. In addition to mitigating urban runoff, the rain garden may contribute to urban habitats for native butterflies, birds, and beneficial insects.

Rain gardens are at times confused with bioswales. Swales slope to a destination, while rain gardens are level however, a bioswale may end with a rain garden as a part of a larger stormwater management system. Drainage ditches may be handled like bioswales and even include rain gardens in series, saving time and money on maintenance. Part of a garden that nearly always has standing water is a water garden, wetland, or pond, and not a rain garden. Rain gardens also differ from retention basins, where the water will infiltrate the ground at a much slower rate, within a day or two.

Soil and drainage Edit

Collected water is filtered through the strata of soil or engineering growing soil, called substrate. After the soil reaches its saturation limit, excess water pools on the surface of the soil and eventually infiltrates the natural soil below. The bioretention soil mixture should typically contain 60% sand, 20% compost, and 20% topsoil. Soils with higher concentrations of compost have shown improved effects on filtering groundwater and rainwater. [18] Non-permeable soil needs to be removed and replaced periodically to generate maximum performance and efficiency if used in the bioretention system. The sandy soil (bioretention mixture) cannot be combined with a surrounding soil that has a lower sand content because the clay particles will settle in between the sand particles and form a concrete-like substance that is not conducive to infiltration, according to a 1983 study. [19] Compact lawn soil cannot harbor groundwater nearly as well as sandy soils, because the micropores within the soil are not sufficient for retaining substantial runoff levels. [16]

When an area's soils are not permeable enough to allow water to drain and filter at an appropriate rate, the soil should be replaced and an underdrain installed. Sometimes a drywell with a series of gravel layers near the lowest spot in the rain garden will help facilitate percolation and avoid clogging at the sedimentation basin. [13] However, a drywell placed at the lowest spot can become clogged with silt prematurely, turning the garden into an infiltration basin and defeating its purpose as a bioretention system. The more polluted the runoff water, the longer it must be retained in the soil for purification. Capacity for a longer purification period is often achieved by installing several smaller rain garden basins with soil deeper than the seasonal high water table. In some cases lined bioretention cells with subsurface drainage are used to retain smaller amounts of water and filter larger amounts without letting water percolate as quickly. A five-year study by the U.S. Geological Survey indicates that rain gardens in urban clay soils can be effective without the use of underdrains or replacement of native soils with the bioretention mix. Yet it also indicates that pre-installation infiltration rates should be at least .25 in/hour. Type D soils will require an underdrain paired with the sandy soil mix in order to drain properly. [20]

Rain gardens are often located near a building's roof drainpipe (with or without rainwater tanks). Most rain gardens are designed to be an endpoint of a building's or urban site's drainage system with a capacity to percolate all incoming water through a series of soil or gravel layers beneath the surface plantings. A French drain may be used to direct a portion of the rainwater to an overflow location for heavier rain events. If the bioretention site has additional runoff directed from downspouts leading from the roof of a building, or if the existing soil has a filtration rate faster than 5 inches per hour, the substrate of the rain garden should include a layer of gravel or sand beneath the topsoil to meet that increased infiltration load. [2] If not originally designed to include a rain garden onsite, downpipes from the roof can be disconnected and diverted to a rain garden for retrofit stormwater management. This reduces the amount of water load on the conventional drainage system, and instead directs water for infiltration and treatment through bioretention features. By reducing peak stormwater discharge, rain gardens extend hydraulic lag time and somewhat mimic the natural water cycle displaced by urban development and allow for groundwater recharge. While rain gardens always allow for restored groundwater recharge, and reduced stormwater volumes, they may not improve pollution unless remediation materials are included in the design of the filtration layers. [21]

Vegetation Edit

Typical rain garden plants are herbaceous perennials and grasses, which are chosen for their porous root structure and high growth rate. [16] Trees and shrubs can also be planted to cover larger areas on the bioretention site. Although specific plants are selected and designed for respective soils and climates, [22] plants that can tolerate both saturated and dry soil are typically used for the rain garden. They need to be maintained for maximum efficiency, and be compatible with adjacent land uses. Native and adapted plants are commonly selected for rain gardens because they are more tolerant of the local climate, soil, and water conditions have deep and variable root systems for enhanced water infiltration and drought tolerance increase habitat value, diversity for local ecological communities, and overall sustainability once established. Vegetation with dense and uniform root structure depth helps to maintain consistent infiltration throughout the bioretention system. [23] There can be trade-offs associated with using native plants, including lack of availability for some species, late spring emergence, short blooming season, and relatively slow establishment.

It is important to plant a wide variety of species so the rain garden is functional during all climatic conditions. It is likely that the garden will experience a gradient of moisture levels across its functional lifespan, so some drought tolerant plantings are desirable. There are four categories of a vegetative species’ moisture tolerance that can be considered when choosing plants for a rain garden. Wet soil is constantly full of water with long periods of pooling surface water this category includes swamp and marsh sites. Moist soil is always slightly damp, and plants that thrive in this category can tolerate longer periods of flooding. Mesic soil is neither very wet nor very dry plants that prefer this category can tolerate brief periods of flooding. [16] Dry soil is ideal for plants that can withstand long dry periods. Plantings chosen for rain gardens must be able to thrive during both extreme wet and dry spells, since rain gardens periodically swing between these two states. A rain garden in temperate climates will unlikely dry out completely, but gardens in dry climates will need to sustain low soil moisture levels during periods of drought. On the other hand, rain gardens are unlikely to suffer from intense waterlogging, since the function of a rain garden is that excess water is drained from the site. Plants typically found in rain gardens are able to soak up large amounts of rainfall during the year as an intermediate strategy during the dry season. [16] Transpiration by growing plants accelerates soil drying between storms. Rain gardens perform best using plants that grow in regularly moist soils, because these plants can typically survive in drier soils that are relatively fertile (contain many nutrients).

Chosen vegetation needs to respect site constraints and limitations, and especially should not impede the primary function of bioretention. 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 to bioretention sites the most when they are located close enough to tap moisture in the rain garden depression, yet do not excessively shade the garden and allow for evaporation. That said, shading open surface waters can reduce excessive heating of vegetative habitats. Plants tolerate inundation by warm water for less time than they tolerate cold water because heat drives out dissolved oxygen, thus a plant tolerant of early spring flooding may not survive summer inundation. [16]

Pollutant Removal Edit

Rain gardens are designed to capture the initial flow of stormwater and reduce the accumulation of toxins flowing directly into natural waterways through ground filtration. Natural remediation of contaminated stormwater is an effective, cost-free treatment process. Directing water to flow through soil and vegetation achieves particle pollutant capture, while atmospheric pollutants are captured in plant membranes and then trapped in soil, where most of them begin to break down. These approaches help to diffuse runoff, which allows contaminants to be distributed across the site instead of concentrated. [24] The National Science Foundation, the United States Environmental Protection Agency, and a number of research institutions are presently studying the impact of augmenting rain gardens with materials capable of capture or chemical reduction of the pollutants to benign compounds.

The primary challenge of rain garden design is predicting the types of pollutants and the acceptable loads of pollutants the rain garden's filtration system can process during high impact storm events. Contaminants may include organic material, such as animal waste and oil spills, as well as inorganic material, such as heavy metals and fertilizer nutrients. These pollutants are known to cause harmful over-promotion of plant and algal growth if they seep into streams and rivers. The challenge of predicting pollutant loads is specifically acute when a rain event occurs after a longer dry period. The initial storm water is often highly contaminated with the accumulated pollutants from dry periods. Rain garden designers have previously focused on finding robust native plants and encouraging adequate biofiltration, but recently have begun augmenting filtration layers with media specifically suited to chemically reduce redox of incoming pollutant streams. Certain plant species are very effective at storing mineral nutrients, which are only released once the plant dies and decays. Other species can absorb heavy metal contaminants. Cutting back and entirely removing these plants at the end of the growth cycle completely removes these contaminants. This process of cleaning up polluted soils and stormwater is called phytoremediation. [16]


Rain Garden Design, Benefits, and Plants

A rain garden is a depression (about 6 inches deep) that collects stormwater runoff from a roof, driveway or yard and allows it to infiltrate into the ground. Rain gardens are typically planted with shrubs and perennials (natives are ideal), and can be colorful, landscaped areas in your yard.

Every time it rains, water runs off impervious surfaces such as roofs, driveways, roads and parking lots, collecting pollutants along the way. This runoff has been cited by the United States Environmental Protection Agency as a major source of pollution to our nation's waterways. By building a rain garden at your home, you can reduce the amount of pollutants that leave your yard and enter nearby lakes, streams and ponds.

Here are some questions to ask yourself if you are interested in installing a rain garden:

  1. Do I have the space in my yard to install a rain garden? A typical residential rain garden is 50 to 100 square feet, depending on the size of the area draining to it.
  2. If I live in an urban area, are there underground utilities that would prevent me from installing a rain garden?
  3. If I live in an urban area, does my municipality require a permit to install a rain garden?
  4. Am I physically able to install the garden, or do I have help? Even small gardens involve moving fairly large quantities of soil.
  5. Large gardens may require the use of heavy equipment. Can I afford to pay for this?
  6. Plant costs can be around $1-2 per square foot. Can I afford to pay for this?

  • Reduce the amount of pollutants that wash into lakes, streams, ponds and wetlands.
  • Help sustain adequate stream flow during dry spells through infiltration and recharge.
  • Enhance the beauty of your yard and the neighborhood.
  • Help protect communities from flooding and drainage problems.
  • Reduce the need for costly municipal storm water treatment structures.

Adapted from University of Wisconsin Extension, Rain Gardens: A How-to Manual for Homeowners.

Smaller gardens can be dug by hand with a shovel, or equipment can be rented for larger gardens. Most gardens for average sized homes can be dug by hand if you are in good health, or have some extra help. Once the shallow depression is dug for the rain garden, it won't take any more time or expense than planting other landscaped areas in your yard.

Build your rain garden to your tastes. While native shrubs and perennials are preferred, you can use other plants (see Plants). This is your garden, you need to like it!


MSU Extension

Rain gardens are a great way to improve the water quality in your community and building one can be a great activity for kids!

Are you looking for a great way to improve water quality for your family and community? Rain gardens might be the answer. Also known as bioswales or rainscaping, rain gardens have many benefits. Over the next few weeks, I will introduce you to these benefits, as well as how to build, plant and maintain a rain garden.

Rain gardens are part of a functional landscape that is a shallow depression dug to catch and soak up storm water run-off. Many hard surfaces produce run-off including roofs, driveways, walkways and even compacted lawns. Rain gardens are used to capture this run-off and filter it naturally, which buffers the lakes, pond, rivers, streams and shorelines in our communities.

Run-off is considered one of the biggest sources of water pollution in our communities and is a concern for many families. Run-off water can contain gas, oil, pesticides and other pollutants that are harmful to our environment and end up in our groundwater and other sources of fresh water.

With the current weather patterns of drought conditions followed by heavy rainfalls, rain gardens are more important than ever. As the rain comes down so fast and so heavy it does not have time to soak into the ground, it is easier for it to pick up pollutants and carry those into our fresh water supplies.

It may seem like one rain garden cannot do much to keep pollutants from the groundwater supply, but just like recycling, when many people ban together it can make a big difference. Rain gardens are becoming more popular as people join together in their communities to make a big environmental impact and save our precious groundwater supply.

According to the U.S. Department of Agriculture, some of the benefits of a rain garden are:

  • Protecting local and regional water quality by reducing sediment and nutrient loads
  • Reducing stream bank and channel erosion
  • Reducing potential flooding
  • Increasing community character
  • Improving quality of life
  • Increasing habitat for wildlife
  • Balancing growth needs with environmental protection
  • Reducing infrastructure and utility maintenance costs

To help communities implement these beneficial gardens, many websites offer information on how to build rain gardens. Most include plant lists and school lesson plans, matched with state standards, so kids of all ages can build a rain garden at school. In addition to doing something good for the community, they’ll be meeting state standards across the curriculum!

With spring just around the corner, I hope you consider a rain garden in your family plans to add new life and purpose to your landscape. Additional articles in this Michigan State University Extension series include: Part 2 - Rain garden plants.

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).

Did you find this article useful?

Please tell us why

Ready to grow with 4-H? Sign up today!

Backyard Fruit 101: Introduction to Growing Your Own Fruits


6. Elderberry ( Sambucus canadensis )

Elderberry grows in zones 3 to 10 and will produce flowers and berries that both humans and wildlife will enjoy. It does well in the basin of the rain garden, where this large, 12-foot-tall shrub will quickly absorb excess rainwater.


Rain Gardens

Rain gardens help reduce sewer overflows and water pollution by absorbing stormwater runoff from hard surfaces into the ground naturally. Since 2006, the Milwaukee Metropolitan Sewerage District (MMSD) and Agrecol Native Seed and Plant Nursery have offered a rain garden plant sale to customers within MMSD’s service area. Plants are provided at a reduced price up to a 50% discount compared to retail prices.

How Do I Order?

To view available plants and to order online click here for the Rain Garden Plant Store.

  • Plants are sold in bundles of 4 each plant's container is 2.5" x 2.5" x 3.5 " (length x width x height/depth) one bundle of 4 plants costs $10.00 unless otherwise noted.
  • Do you wanted to create a rain garden but need help selecting the plants? Try a garden kit that helps take the guesswork out of gardening. Each kit contains 16 plants and provides coverage for a 15 to 25 square foot garden.

Who can order?

Any private property owner, local non-profit group, or municipality can purchase plants. Plants cannot be purchased for resale. If you are unsure of your status or have other questions, please submit your request on the contact us form.

Need Help Selecting Rain Garden Plants?

Come to one of our FREE virtual rain garden workshops on Saturday, March 13th from 10:00 AM to 11:30 AM or Tuesday, March 23rd from 10:00 AM to 11:30 AM. The workshop will focus on how to design and build a rain garden, how to select plants, and how your rain garden can help protect Lake Michigan. At the workshop, gardening experts will be on hand to discuss design tips and assist you with creating your rain garden. This is a FREE workshop, but you must register and spots are limited.

Join gardening expert, Melinda Myers, for a FREE virtual webinar "How to Select Rain Garden Plants", on Wednesday, March 24th from 6:30 to 7:30 PM. Selecting the right plant for the growing conditions is always an important step when planning and planting a garden. It is even more critical when it comes to rain gardens. Melinda will cover a variety of rain garden plants from short to tall, for sun and a few for the shade. She will also help you plan for color and interest throughout the year as well as select plants that attract pollinators and support songbirds. This is a FREE webinar, but you must register.

Dates to Remember:

  • March 13th: Virtual Rain Garden Workshop. Sign up here.
  • March 23rd: Virtual Rain Garden Workshop. Sign up here.
  • March 24th, 2021: Virtual Webinar "How to Select Rain Garden Plants" with Gardening Expert, Melinda Myers. Register here.
  • April 8th, 2021: All orders must be submitted online by the close of business. Click here for the Rain Garden Plant Store
  • May 13th, 2021: Virtual Webinar "How to Plant Your Rain Garden" with Gardening Expert, Melinda Myers. Register here.
  • IMPORTANT UPDATE: DUE TO UNPRECEDENTED DEMAND, WE NEED TO HAVE 2 DIFFERENT PICK-UP DATES. If you ordered your plants prior to March 24th, your pick-up date will be June 12 th . If you order your plants on March 24 th through April 8 th (sale end-date) your pick-up will be either June 12 th or June 26th. We will email you your plant pick-up date in mid-April. Plant order pickup is at MMSD - 260 W. Seeboth St., Milwaukee, WI 532042.

To receive future notifications on MMSD plant sales and workshops, sign up for our Fresh Coast News email list.


Watch the video: HOW A FRENCH DRAIN WORKS