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  • 8/3/2019 Rainy Day Gardens - American Horticultural Society

    1/537March / April2003

    AN I DE A WHOS E time hascome, rain gardens are stormingthe country, showing up in pri-

    vate gardens, arboretums, housing devel-opments, parking lots, and alongroadways from the Chesapeake Bay toPuget Sound. In Seattle, theyre part of aSalmon Friendly Gardening program,

    while in Maryland they are being pro-moted as a way to Save the Bay.

    If you havent heard of a rain gardenbefore, the basic concept is quite sim-plethey are designed gardens orplantings that help capture and cleanstorm water runoff from gutters, drive-

    ways, lawns, and other impermeable orsemi-permeable surfaces. This helpsprevent soil erosion and reduces theamount of pollutants entering our riversand ground water.

    National interest in storm water man-agement has been increasing exponen-tially because of the growing concernabout non-point source (NPS) pollution,

    which the U.S. Environmental Protec-tion Agency (EPA) now considers theleading cause of water quality problems

    Rainy-Day Gardens

    Imaginative plantings that help capture and clean runoff are attracting the attention of home

    gardeners, landscape designers, and watershed managers. BY MARYALICE KOEHNE

    Above: Lorrie Otto used only native plants to

    create this rain garden in Bayside, Wisconsin.

  • 8/3/2019 Rainy Day Gardens - American Horticultural Society


    in the United States. Unlike pollution

    that can be traced directly to onesourcesuch as an industrial plant or asewage treatment facilityNPS pollu-tion is caused by a variety of manmadeand natural pollutants that are picked upby runoff and then deposited into waterbodies and water sheds. These pollutantsinclude fertilizers, pesticides, oil, grease,de-icing salts, heavy metals, bacteriafrom animal wastes, and even sediment.

    EPA studies indicate that as much ashalf of all pollutants in stormwater comefrom home landscapes, and some com-munities are now requiring home andbusiness owners to find ways to avoiddischarging stormwater into sewers. Ifyou consider that a city block generatesnine times more runoff than a woodlandarea the same size, it makes even moresense to plant rain gardens.

    Rain gardens have been part of newhousing developments and road construc-tion projects for more than 20 years, butthey have often been saddled with clunkyand unromantic names such as bioreten-

    tion ponds, low impact developments

    (LIDS), infiltration basins, stormwatermarshes, and even wet gardens.Consultants to the Prince Georges

    County, Maryland, Department of Envi-ronmental Resources (DER) are credited

    with coining the term rain gardens,which helps convey the idea of relativelysmall, colorfully planted areas that collectrain water or snow melt. In home gardens,they are typically located near the down-spouts of gutters, or in areas where watertends to wash off a sloping driveway. The

    water routed to these areas is filtered nat-urally by the gardens plants and soils. Asan added bonus, these plantings attractand provide habitat for birds, butterflies,and other beneficial wildlife.

    TAKING A CUE FROM NATUREAs with many successful ideas, the eco-logical model for rain gardens comes fromnature, where vegetation, soil, and soil or-ganisms slow down, filter, and store rain-

    water. Mature forests are particularlycritical components of this process be-

    cause over time they have developed a

    spongy litter layer that absorbs water andallows it to slowly percolate into the soil, where it replenishes watersheds andaquifers. According to the EPA, nationalforests alone are responsible for capturingand filtering the drinking water used bymore than 60 million Americans.

    Its not so much that this is a newidea, says Carole Barth, an environmen-tal planner with the Prince GeorgesCounty DER, but were putting back

    water in the environment like Mother Na-ture did before we messed it up.

    Using the catchy slogan From Rain-bows to Rain Gardens, the DERs goal isto foster a million rain gardens to helpprotect the Chesapeake Bay through anoutreach program that extends to MasterGardeners, garden clubs, local watershedgroups, and schools.

    In other words, rather than continuingto treat rainwater like a waste product byfunneling it into stormwater sewer sys-tems, its being valued as the precious nat-ural resource that it is.

    38 the American Gardener


    Rainwater is directed away

    rom the house to a naturally

    ow spot in the yard by means

    f a gutter extension pipe,

    hown here, or French drains.

    The outermost, driest

    edge of the garden can

    be planted with anytrees, shrubs, and

    herbaceous perennials

    suited to your region

    and site.

    Small stones or pebbles at

    the terminus of the pipe

    create a free-draining area

    for excess water to collect

    initially before seeping into

    the garden itself.

    The middle planting zone of the garden is suit-

    able for plants that prefer consistently moist

    soil but tolerate periods of drought. Examples:

    sweetbay magnolia (Magnolia virginiana), river

    birch (Betula nigra), swamp azalea (Rhodo-

    dendron viscosum), cardinal flower (Lobelia

    cardinalis), switch grass (Panicum virgatum),

    black-eyed Susan (Rudbeckia hirta).

    The lowest zone of the garden is

    ideal for plants that like wet feet

    most of the time but can with-

    stand occasional dry spells. Ex-

    amples: New England aster

    (Aster novae-angliae), sedges

    (Carexspp.), marsh marigold

    (Caltha palustris), swamp milk-weed (Asclepias incarnata).

    A layer of mulch over the

    rain garden reduces weeds

    and helps filter runoff.The saucerlike depression of the rain garden, which should

    be fairly shallow and no more than a foot or so deep in the

    center, is filled with a mixture of soil, organic matter,

    sand, and gravel to permit good drainage.

  • 8/3/2019 Rainy Day Gardens - American Horticultural Society

    3/539March / April2003

    FINDING A SITELate winter to early spring, when snowsmelt and rains fall, is the perfect time toevaluate your property to see if you canbenefit from creating one or more raingardens. Look for a low point in youryard where water tends to pool afterstorms, or an area along the street ordriveway where you get a washout everytime it rains. If you have had to add ex-tenders to your gutters or install a Frenchdrain to route water away from thehouse, you may have perfect conditionsfor a rain garden.

    There is no single formula for creatingrain gardenstheir shape, size, and plant-ings depend on many factors, including

    where you live. But even a relatively smallrain garden can help alleviate runoff prob-lems. Consider starting with just one smallplot that can easily be dug by hand, thenextend it or add others later. If you have asteeply sloping lot or get a high volume of

    water flow during major storms, you maywant to consult a landscape architect.Rain gardens should always be set wellaway from buildings, so theres no chanceexcess water could flow into the basement.

    What rain gardens usually have incommon is a relatively shallow saucer- orbowl-shaped depression where runoff ini-tially collects. The soil in the bottom ofthis depression is often amended with ablend of organic matter, sand, gravel and

    mulch to facilitate drainage. A slightlyacidic soilwith a pH of 5.5 to 6.5hasbeen found to be ideal for the type of bio-chemical reactions that remove pollutants.Some rain gardens include an underdrainsystem or an overflow outlet to handle ex-cess water during heavy storms.

    The key is that the central basinshouldnt be so deep that water will standin it long enough to kill plants or allowmosquitoes to breed in summer. If wateroverflows the depression during a heavystorm, it should be absorbed by plantingsaround the perimeter.

    Before planting your rain garden, ex-perts advise that you watch how the sitehandles two or three rainfalls. This will

    SOLVING PROBLEMS AT HOMES AND SCHOOLSRain gardens at three very different sites in and around Milwaukee, Wisconsin, illustrate how diverse such gardens can be

    and how they can be used both to solve drainage problems and to create beautiful, interesting plantings.

    When Katie and John Clark were looking for something to replace the scraggly, balding lawn that underlay their wooded front

    yard, the idea of a meandering dry river bed seemed like a practical solution. But once runoff water began tumbling over small

    waterfalls in their new installation and woodland plants began to thrive, they realized that besides solving aesthetic problems,

    this new installation at their home in Elm Grove, a suburb of Mil-

    waukee, boasted many advantages. During storms, when rainwa-

    ter gushes down the driveway from the cul-de-sac that fronts their

    house, it now courses through the channel to a wooded area be-

    hind their house. As the runoff from their property and the street

    pools there, i t soon infil trates the soil and helps recharge and re-

    new the groundwater.At Indian Hill School in Brown Deer, a northeastern suburb,

    students routinely use a rain gardenas well as prairie and

    woodland plantingsas part of science lessons and projects.

    Begun in 1990, this verdant paradise fronting the modern, flat-

    roofed building was destined to become a formal garden before

    several mothers and local environmental activist Lorrie Otto lob-

    bied the school board to install more naturalistic plantings. Wa-

    ter that flows through the rain garden eventually drains into a

    pond that hosts frogs, dragonfl ies, and other wildl ife. This is

    our outdoor classroom, said principal Rebecca Bell. Each

    teacher uses it differently and ties it into the curriculum.

    Otto has solved runoff problems in her own garden with what

    she calls a drainage ditch that goes nowhere. This early ver-

    sion of a rain garden she created in the grass-clad drainage

    ditch that ran alongside the street in the front of her yard initially drew the ire of city officials. The city soon let her have her

    own way, however, and now stands of mature native plants such as white turtlehead (Chelone glabra), Indian grass (Sorghas-

    trum nutans), and Joe Pye weed (Eupatorium fistulosum) edge a pond that collects filtered street runoff.

    A lifelong environmental activist, this feisty 83-year-old is one of the founding members of Wild Onesan organization

    that advocates naturalistic gardeningand is credited with fostering passage of legislation banning use of the pesticide DDT

    in Wisconsin in 1970, two years before Congress outlawed the pesticide nationally.

    I think there should be ordinances saying you must keep the rain water that falls on your property right there, says Ot-

    to. On this issue, at least, ci ty off icials around the country are finally beginning to see eye to eye with her. M.K.

    A rain garden at Indian Hill School in Brown Deer, a suburb of

    Milwaukee, Wisconsin, filters water that eventually drains into

    this pond. The rain garden and pond are integral parts of the

    schools outdoor cla ssroom activities a nd science projects.

  • 8/3/2019 Rainy Day Gardens - American Horticultural Society


    allow time for the amended soil in thebasin to settleif it settles too much, youmay need to add more soiland will letyou see how long water stands in thebasin. If you still have standing water afterthree days, you may need to improve thedrainage.

    Plants should be selected to fit the sitechosen for the rain garden. Determiningthe exposure of the locationdegree ofsun or shadeis particularly important.

    Rain gardens generally have two orthree planting zones. The innermostplanting zone in the bottom of the centralbasin should include plants that are happyhaving wet feet most of the year but that

    will also tolerate periods of droughtplants native to wetlands are good choic-es here. The second planting zone, on thesloping walls of the central basin, should

    include plants that tolerate periodic im-mersion and are also drought tolerantplants native to the edges of streambanksare appropriate here. The third plantingzone, around the perimeter of the basin,can include a variety of herbaceous peren-nials, shrubs, and even trees suited to yourregional soil and climate.

    Experts advise that all planting areas inrain gardens be covered with two or threeinches of organic mulch. Research hasshown that in addition to reducing weed

    problems, the mulch helps remove pollu-tants from the water filtering through it.As the concept of rain gardens spreads

    rapidly, plant lists suited for different areasof the country are becoming availablethrough regional university Extensionagencies, departments of environmentalprotection, and some specialty nurseries(see Resources, page 41).

    Usually, a minimal financial invest-ment can yield an attractive addition toyour landscaping.

    REDUCING SUBURBAN RUNOFFExisting neighborhoods of major cities arealso benefiting from rain gardens that slowthe rush of storm water into municipal re-tention ponds and sewage facilities. For ex-ample, Seattle, Washington, claims thatthe innovative Street Edge Alternative(SEA Street), completed in 2000 by theSeattle Public Utilities and the Seattle De-partment of Transportation, is the first ofits kind in the country. The project in-volved city agencies working directly with

    individual property owners in a three-and-a-half block area along a busy street in a1950s subdivision that was built withoutcurbs or gutters (see photographs above).

    Previously, ditches along the edges ofthe properties carried a high volume of

    water that was contributing to the over-load of Pipers Creek, a nearby waterway.Now, the flow is stemmed by a series ofcarefully designed plantings that run thelength of the road. Each homeowner wasable to chose from among six varieties ofdeciduous trees, five evergreens, 20 shrubs,10 herbaceous perennials, two low-grow-ing ground covers, and six types of wet-land plants. While city workers did theplanting, property owners are responsiblefor maintaining the gardens.

    The prototype project has proven sosuccessful that this technique is being ap-plied to other streets that are subject to se-vere stormwater runoff.

    Another innovative urban rain gardenproject is on display in the Swede Hollowneighborhood of St. Paul, Minnesota,

    where the neighborhood association joinedforces with the city to help protect a re-stored wetland area along the MississippiRiver from polluted runoff. Two vegetatedswales funnel stormwater from a street in-to the 900-square-foot Maria Bates RainGarden, designed by Barr Engineering.

    Local elementary school students plant-ed the garden, which features a diverseblend of native and adapted exotic plantssuch as big bluestem (Schizachryium sco-

    40 the American Gardener

    In Seattle, severe runoff problems in one neighborhood were solved by creating rain gardens

    along the length of an entire street. Top: Before construction of rain gardens, runoff from this street

    flowed into a local creek. Above: Rain gardens not only absorb runoff but look great.

  • 8/3/2019 Rainy Day Gardens - American Horticultural Society


    parium), New England aster (Aster novae-angliae), blazing star (Liatris aspera), black-eyed Susan (Rudbeckia fulgida Goldsturm,and feather reed grass (Calamagrostisacu-tiflora Karl Forster). Neighborhood artistsadded a meandering walkway with signagethat helps explain the gardens function,and benches encourage passersby to stopand savor the colorful plantings.

    The Seattle and St. Paul rain gardens arevoluntary efforts to reduce stormwaterrunoff, but some municipalities are mov-ing toward mandatory programs.

    In Milwaukee, a new law will require45,000 homeowners and businesses to dis-connect downspouts from sanitary sewersserved by the Milwaukee MetropolitanSewerage District (MMSD) by 2007. Anestimated 200 million gallons of rainwaterthat falls during heavy storms will thus bedirected back to the ground, which shouldeliminate the citys need to dump dilutedsewage into creeks, the Milwaukee River,or Lake Michigan every time three to fiveinches of rain falls quickly.

    The district hopes to disconnect down-spouts from 10,000 homes a year and will

    pay homeowners $50 per disconnecteddownspout beginning in 2004. By 2007,disconnections will be mandated. Besidesrain gardens, green roofs, rain barrels, roofrestrictors, and increasing the tree canopyare options the district intends to pursue.

    RESTORING PARADISE TO PARKING LOTSDesigning rain gardens in association

    with parking lotswhichare major sources of bothpollution and runoffissomething many municipal-ities, botanical gardens, andbusinesses are exploring.Weve installed a demon-stration rain garden thatcatches runoff from theparking lot at the new Alter-ra Coffee House/Milwaukee

    Flushing Station on thelakefront, says KevinShafer, executive director ofMMSD.

    Botanical gardens and ar-boretums see rain gardens asimportant elements of edu-cational and environmentalprograms. In cooperation

    with the Virginia Depart-ment of Forestry, the BlandyExperimental Farm near

    Boyce, Virginia, installed arain garden at its visitorsparking lot in 2001. And arain garden is planned aspart of new parking areasbeing constructed duringrenovation of the visitor cen-

    ter at the Minnesota Landscape Arbore-tum in Chanhassen.

    As we look for ways to reconnect ourgardens with the natural world around us,its important to keep in mind that no gar-dens are truly natural. Wherever humansettlement disrupts nature, problems de-velop unless people remember the wordsof conservationist Aldo Leopold: Theprivilege of possessing the earth entails theresponsibility of passing it on the better forour use. Rain gardens are one way to re-duce our own environmental footprint

    while at the same time creating a beauti-ful addition to our landscapes.

    Maryalice Koehne is a free-lance writer who

    lives and gardens in Wauwatosa, Wisconsin.

    41March / April2003

    ResourcesEnvironmental Protection Agency,


    Friends of Bassett Creek (a private con-

    servation group in Minneapolis, Min-

    nesota), www.mninter.net/~stack/rain/

    GreenSpace Partners (a community

    group in Minneapolis, Minnesota),


    National Wildlife Federations Back-

    yard Wildlife Habitat Program,


    Natural Resources Defense Council,



    Prince Georges County, Maryland, De-

    partment of Environmental Resources,

    (301) 883-5852 / (301) 883-5834




    s Offers booklet, new bioretention

    plant list of 150 hardy plant species.

    Seattle SEA Streets project,


    University of Wisconsin Extension

    Service, Madison WI. (608) 262-

    3346 or toll-free (877) 947-7827.


    s Offers publication titled Rain Gar-

    dens: A Household Way to Improve

    Water Quality in Your Community.

    Virginia Department of Forestry,



    Wild Ones, www.for-wild.org

    Wisconsin Department of Natural Re-

    sources, Madison, WI. (608) 264-

    6217. www.dnr.state.wi.us/

    s Offers pamphlet titled Rain Gar-

    densNatures Way to Control

    Runoff Pollution.

    Above and top: At the Maria Bates Rain Garden in St. Paul,

    Minnesota, students from a local elementary school planted

    the garden with a mixture of native and adapted exotic plants.