Maine: Adding a Rain Garden to Your Landscape

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Adding a Rain Garden to Your Landscape


  • 1.Landscapes for Maine PHOTO: EDWIN REMSBERG, USDA-CSREES Adding a Rain Garden to Your LandscapeBulletin #2702What Is a Rain Gardenlonger running over the surface of the land, it cannot transport complement any home style, as there are many choices of shapesand Why Would Youpollutants to nearby streams viaand plants that can be surface runoff or storm drains. incorporated into your garden.Want One?Rain gardens are easy and Rain gardens can even attractA rain garden is a depressioninexpensive to install andbirds and butterflies!in the ground that is planted with maintain. Since they are flexiblewater-loving native perennials and in size, shape, and appearance, Do rain gardens harborshrubs. Water from a downspout they can fit into almost anymosquitoes?or other source flows into the rainlandscape and lifestyle. A properly constructed rain gardengarden, where it soaks into theRain gardens are beautifulwill drain water, not hold it. In aground and is used by the plants.well-designed rain garden, water In addition to adding beautywill soak into the ground in a day.Rain gardens make senseto lawn areas with height and Mosquitoes will not survive in color, rain gardens can replace areas that dry out in seven daysRain gardens help protect theor less after a summer rain,water quality in our lakes, streams, lawn areas, which would because the development of aand rivers by reducing the amountotherwise need mowing, with anmosquito from egg to adult takesof polluted runoff reaching theseinteresting combination of native longer than seven days.resources. If designed and installed plants. Rain gardens can alsocorrectly, rain gardens reduce the eliminate unsightly erosionamount of runoff from hard,problems on your property byPlanning for Your Rain reducing excess water fromimpervious surfaces by up to 98 rooftops or driveways. They can Gardenpercent. As this water is no Choose a locationHow rain gardens remove pollutantsFollow these placementPollutant Removal Mechanism Pollutants Removed guidelines to help make the rainAbsorption to soil particlesDissolved metals and soluble phosphorusgarden more enjoyable for youSmall amounts of nutrients including phosphorusand your neighbors:and nitrogenMicrobial processes Organics, pathogensRemember that the purposeExposure to sunlight and drynessPathogensof the rain garden is to put water into the ground! PlaceInfiltration of runoffMinor abatement of localized flooding, minorincrease in localized base flow of groundwater,your garden at least ten feetallowing some nutrients to be removed whengroundwater flows through bufferSedimentation and filtrationTotal suspended solids, floating debris, trash, soil-bound phosporus, some soil-bound pathogensBrix, H. "Wastewater treatment in constructed wetlands system design, removal processes, and treatmentperformance." In Constructed Wetlands for Water Quality Improvement, ed. G.A. Moshiri, 922. Boca Raton, Fl:CRC Press, 1993. Adapted in W. Hunt and N. White, Designing Rain Gardens. NC State University CooperativeExtension, 2001.

2. away from your foundationon lakefront, stream front, orunsightly. You may prefer toin order to avoid watercoastal property, contact yourcarry your water undergroundseepage in your basement.local code enforcement officervia plastic or PVC pipe. before you begin. If you live Grass-lined shallow ditches,Do not place a rain garden in Maines unorganizedor swales, can be used to directover a septic tank or leach territory, contact the Land water to the rain garden. Thesefield. Use Regulation Commission ditches should be gently slopedDo not place a rain garden (LURC) at 207-287-2631. to avoid erosion. The side slopesnear your drinking water well. of the ditch should be no steeper Determine how big yourthan a 2:1 ratio (a one-foot rise forBe aware of and avoidrain garden should beunderground pipes andevery two feet across).utilities. If you dont know For best water qualityIf you expect heavy flows ofwhere they are, call Dig Safe treatment benefits, the rain garden water (e.g. from a large drivewayat 1-888-DIG-SAFE (344-7233) should hold the water from aarea), a rock-lined ditch isat least three days before one-inch rainstorm. An easy way advisable. Line the ditch withdigging. Outline the proposedto ensure this is to make the rainlandscape fabric in order toarea with white paint. Dig garden 30 percent of the drainage prevent it from eroding.Safe will automatically notifyarea. To calculate that volume, Stabilize the area where theall of its member utilitiesfigure out the size of the rooftop, water enters your rain garden(gas/oil/steam, electric,driveway, or other impervious with stone to prevent erosion ofcommunications, water, and surface that will drain into your the rain garden. Watch this areasewer) that own undergroundgarden in square feet, and make carefully during the first fewfacilities in the area of thethe garden area 30 percent of thatrainstorms following installation.excavation so that they canarea. For example, a 1000-square-mark their facilities. foot rooftop would require a 300- square-foot rain garden.Check for any private wiring You can make the rain gardenI have a lot of standing wateror underground utilities. larger than 30 percent of the on my property. Can I still haveLook around for lights in the drainage area, or as small as 20a rain garden?yard, such as spotlights on percent. Simply use 30 percent as Rain gardens are designed toflagpoles or signs, lights at a guideline.infiltrate water. Standing waterthe end of the driveway, and indicates poor infiltration, and wesheds with electricity.Decide how to channel the do not recommend directingPlace the rain garden in a flatwater additional water to these naturally wet areas.area if possible to make How you direct water from theinstallation easier. downspout, driveway, or otherDo not place the rain garden hard surface to the rain garden isin a naturally wet area. Wet a matter of choice. Some commonspots may seem ideal, butmethods include gutter extensions,they will drain too slowly.piping, and ditches. Gutter extensions are simplyAvoid trees and tree roots, as metal gutter pipes attached to thethey may be injured by nearby ends of your downspouts. Theydigging and may not tolerate must be angled downwardadditional moisture in the soil. slightly for the water to flow. TheMaine has mandatoryadvantage of gutter extensions isprotective Shoreland Zoningthat they are easy to install.regulations. If you are workingHowever, some people find them2 UNIVERSITY OF MAINE COOPERATIVE EXTENSION 3. Plan ahead for grass central portion of the garden the lowest portion of the rainremovalmust be six inches below thegarden, and dry-tolerant plants grade of the surrounding land infor the edges.If the rain garden is located in order to temporarily hold water.Use native plants wheneveran existing lawn, you may want Gently slope the garden to this possible. Native plants willto kill the grass before digging.lowest point to avoid erosion survive better in our environment.This takes some forethought, aswithin the garden. A one-inch For help selecting native plantsyou will need to lay black plastic drop for every foot across is a that meet your light, moisture,or a tarp on the lawn until thegood rule of thumb. For a 300-and height requirements, consultgrass dies (doing this over thesquare-foot rain garden, choicesour bulletin #2500, Gardening towinter works best).include a circular garden with aConserve Maines Native Landscape.Do NOT use a weed killer such20 foot diameter, or a longer,This bulletin specifies the lightas Roundup to kill grass. You narrower garden approximately and moisture needs and eventualcan always simply remove the 10 feet by 30 feet. height of native perennials andsod as you excavate the garden,Remember that rain gardensand use it elsewhere if possible.on slopes will need to be dugEstimate your cost more deeply into the high side of the slope to produce a levelBuying your plants The cost will depend on how bottom. You will need to build amuch work you decide to do berm, or hump, on the lower end Buy plants with healthy rootyourself. If you do all of the work systems. The healthier the root to keep the water in the garden. system, the quicker your plants willdigging the garden, buying the The design stage provides anbecome established. Use onlyplants, planting, and mulchingopportunity to get creative. Whilenursery-propagated plants oryour costs will range from three tothinking about the shape of the those from your own garden. DOfive dollars a square foot. If you garden as well as the color, shape, NOT collect plants from the wild. Ifhire a landscaper to do some oryou buy bare-root perennials, be and height of the plants, considersure to keep the roots moist untilmost of the work, such as design adding elements such as stone oryou plant, excavation, or planting, the fencing, or set a bench cost could approach ten to Personalize your garden!Plugs will get you more plants for less money. These small-fifteen dollars a square foot. sized seedlings grown in trays Select plants for yourtake longer to fill in the space inDesigning Your Raindesignyour garden, but plugs can help keep costs down.GardenWhen selecting plants, consider zone hardiness,Most reputable nurseries have selections of native plants. If youDetermine shape and sunlight needs,are unsure, ask nursery staff! Theyplacement moisture needs,are very knowledgeable, and will soil type needs, often have other suggestions if aOnce you have calculated the particular plant is not available. height and width,size of your rain garden, determineAlso, asking for native plants may color,a general shape, and position theconvince nurseries to offer more of texture, and them. For sources of native plants,garden within your landscape. whether they are native. consult our bulletin #2502, NativeHave fun, and explore two or Plants: A 2002 Maine Source Listthree options before making aIs your site shady or sunny?(see Resources section).final design decision. Remember that it takes more thanRain gardens can be circular,six hours of sunlight to be Plan ahead. Nurseries will have a larger selection in the spring thankidney-shaped, or long and considered full sun. Choose at the end of the summer. Younarrow. The shape of the gardenplants that will perform well inmay have to visit multipledepends on your wants andthe light you have available. nurseries if you want a largeneeds. Just remember that aChoose water-loving plants fornumber of a particular plant. ADDING A RAIN GARDEN TO YOUR LANDSCAPE, BULLETIN #2702 3 4. shrubs. Plants designated H Once you know the size, shape, Cover the berm with grass or(hydric) will do well in the lowest, and location of the rain garden, mulch to prevent erosion. If youwettest areas of the rain garden,its time to get your hands dirty! seed the berm, use straw towhile M (mesic) to S (sub- If you do all the work yourself, itprevent it from eroding until thexeric) will do well in the drier areas.may take the better part of a day. grass takes hold.Another good resource is The Consider inviting friends to makeBuffer Handbook Plant List, whichthe work faster and more fun.Plant your rain gardenindicates whether plants will doFirst, delineate the outline ofThis is the fun part!well in wet, moist, or dry the rain garden on the ground. YouSet your plants out in theconditions, and includes native as can use a garden hose, string, orgarden to match your design. Nowwell as noninvasive, nonnative spray paint. Be flexible. Even the you can adjust the position of theplants. (See Resources section for most carefully sketched plan may plants, if necessary, before youboth publications.)need to be adjusted to fit the area. start planting. If possible, keepIf you have not already killedthe plants in their pots to preventInstalling Your Rain the grass in your garden area with them from drying out before they a black plastic or other covering, are planted. Wrap bare-root plantsGarden you will need to remove the sodin wet newspaper until planting. as you excavate the garden. DoRemember that you dont wantAvoid wet conditions NOT use a weed killer such asto compact the soil. Work fromBe sure to install your rain Roundup to kill the side of the garden to the othergarden when the soil is dry. If you Try not to compact the soil asto reduce the amount of foot trafficdisturb wet soils, you compact you dig the rain garden. Workin the garden. If you think thatthe soil to the point that water from one side to the other side, oryou have packed the soil downcan no longer infiltratewhich from the center to the outside, so too much, use a rake to loosen it.will defeat the entire purpose of ayou dont pack down the soil. Dig each hole twice as wide asrain garden!Loosen the soil at least twothe pot and deep enough to keep feet deep. Even though the gardenthe crown of the plant level withDig your gardenwill only be six inches deep in thethe ground. Make sure your plant center, loosening the soil will help is level, then fill the hole with soilSoil mix matters your plants establish root systems and pack the soil around theThe rain garden should allow in this new environment. Now isplant to remove any air pockets.water to easily seep into thethe time to add compost or otherWater immediately afterground. If your soil is mostly clay, soil amendments if needed. planting. Giving the plants a goodyou may need to amend the soilUse extra soil to create a berm soaking will give your rain gardento make it more permeable. A on the downslope side of the a good start. Use a watering can ifrecommended soil mix is 50 to60 percent sand, using native soil garden. The berm will act as a possible: a high-pressure blastfor the remainder. Adding up towall to hold water in the garden from a hose will push soil away20 percent compost in place of during storms. Make the berm from the plant and keep the waternative soil will enhance initial three to six inches high and eightplant growth, and high-clay soils from soaking in, doing more harmwill need even higher amounts of to twelve inches wide, with gently than good. Water the new plantscompost, organic matter, or topsoilsloping sides. Taper it off as itbefore adding mulch to ensureto increase soil permeability. wraps around to the inlet of the that the maximum amount of rain garden. Now stomp on it!water reaches the roots. This soil needs to be compacted to hold the water in the gardenMulch your garden before it soaks into the ground.4 UNIVERSITY OF MAINE COOPERATIVE EXTENSION 5. The value of mulch is oftenoverlooked. Mulch is important Maintaining Your Rainmaintenance: weeding, pruning,plant replacement, mulching, andin any garden to keep plants Garden supplemental watering duringmoist and discourage weeds. dry spells.Layering sheets of newspaperWatch your rain garden theWhile some people trim deadaround the plants before addingfirst time it rains. Where does thestems and leaves from theirmulch will provide an addedwater go? Does it pond where perennials before winter, you canweed intended it to? Or are the leave them over the winter toApply a three- to four- inch moisture-loving plants left high provide food for birds and wildlife.layer of mulch to your rain garden.and dry? Does the force of the Once new growth appears in theBe sure to keep the mulch away water erode the mulch and soil atspring, remove the dead stemsfrom the crown of each plant.the entrance to the rain garden? and leaves.Add some additional mulch each Use the first few storms to evaluateyear for a few years, until theyour garden. If the contours needSolving plant problemsplants have matured, so the soil to be adjusted, use a rake orHere are some considerationsdoes not dry out too quickly.shovel as needed. Strategicallyif your rain garden plants fail toAfter a few years, mulch is notplaced rocks can slow the force ofthrive:necessary, unless you prefer its the water.more formal appearance. If you have used shallowNew plants need a consistentHow much mulch will youditches or swales to direct watersupply of water until theirneed? A cubic yard1 of mulch willto the rain garden, inspect theseroots are establishedevencover a 100-square-foot area withditches often to be sure that thethough your rain gardenabout three inches of mulch. bottoms are not eroding. Keeping catches stormwater. Your rainWith the exception of bark the side slopes of the ditches nogarden will need one to twochips and artificially colored steeper than 2:1 (for every twoinches of water per weekmulches, you can generally use feet across, a one-foot rise) will during the first year.any type of mulch that will stay help prevent erosion.Consider the location of eachin place and retain moisture. BarkKeep in mind that during theplant within the garden.chips dont work because theyfirst year, especially during theSome plants will not toleratetend to float away in rain gardens,dry summer months, you may having their roots dry out,and artificially colored mulch willneed to water the rain garden so while others do not like themleach color into the soil. We have that the plants can get established. to be moist all the time.used Superhumus and ErosionUse a rain gauge to keep track of the rainfall. Your rain garden willDouble-check the hardinessControl Mixblended products need one to two inches of waterzone rating of your plants. Iffrom earthlifein our test rain per week the first year. you end up replacing plants,gardens with success. If you areFrequent weeding will bechoose plants rated for aunsure, ask your nursery necessary in the first few years colder zone than yours, toprofessional. before plants become established.ensure that they can surviveNurseries sell mulch by the In order to distinguish betweenthe very coldest temperaturesbag and by the cubic yard. If you weeds and young plants, consider they might experience.dont have access to a truck, mostnurseries will deliver for a adding plant labels next to each Make sure that you havenominal fee. plant. used plants well suited to theOnce the plants mature andlight levels and light duration become established, maintenanceof your gardens location. of a rain garden is nothing more than routine landscape127 cubic feet, or about what will fit inthe back of a pickup truck ADDING A RAIN GARDEN TO YOUR LANDSCAPE, BULLETIN #27025 6. Example of a Sunny Rain Garden Design Plant List for a SunnyRain GardenPlants for the wetter center of thegarden:Woody shrubs:*SS: Clethra alnifolia, summersweet. 56H x46W. Late-to-emerge foliage. Fragrant,large, white flower stalks in summer.Perennials:**CA: Lobelia cardinalis, cardinal flower. 24Hx 1W. Bright red flowers from July toSeptember.T: Asclepias tuberose, orange butterflyweed. 23H x 23W. Can handle dryareas. Orange blooms from June toSeptember.I:Iris versicolor, blue flag iris. 24H x24W. Blue flowers in spring.M: Caltha palustris, marsh marigold. 8H x1W. Glossy heart-shaped leaves withbright yellow flowers in the spring.J: Eupatorium maculatum, joe-pye weed.35H x 12W. Red stems, purple-redflowers from July to September.SM: Asclepias incarnate, swamp milkweed.23H x 23W. Will not tolerate drought.Showy, flat, reddish flowers from July toOctober.Plants for the dryer outer edge ofthe garden:Woody shrubs:*P: Potentilla arguta, tall cinquefoil. 13H x 13W. Thick leaves and many white flowers all summer.Perennials:**G:Geranium maculatum, wild geranium.12H x 2W or more. Purple flowers inthe late spring and sometimes again inthe fall. Pretty foliage.A: Anemone canadensis, windflower. 2H x10W. Pure white blossoms in June.Large, attractive leaves.LO: Lobelia spicata, spiked lobelia. 35H x35W. Blue flowers from June toAugust.FA: Symphyotrichum umbellatus, flat-toppedaster. 37H x 37W. White toyellowish-centered flowers in the fall.AS: Symphyotrichum novae-angliae, NewEngland aster. 37H x 37W. Purpleflowers in the fall.H: Helenium autumnale, perennialsunflower, 35H x 23W. Lots of yellowflowers in the fall.*Woody shrubs: Though they may shedtheir leaves, the woody structure of theseplants will provide winter interest in thegarden.**Perennials: These plants die over thewinter and sprout new shoots in the spring.Sometimes some of last years foliage willsurvive the winter, but generally you shouldtrim off the dead foliage in late fall and waitfor the green growth of spring.6 UNIVERSITY OF MAINE COOPERATIVE EXTENSION 7. Plant List for a Shady Example of a Shady Rain Garden DesignRain GardenPlants for the wetter, shadiercenter of the garden:Woody shrubs:*HV: Hamamelis vernalis, vernal witch hazel.610H x 610W. Showy golden yellowfall color. Long-lasting, scented yellowflowers in the late winter.RH: Rhododendron canadense, rhodora(native rhododendron). 13H x 13W.Showy purple flowers in the spring.Tolerates wet, acidic soil.LE: Ledum groenlandicum, Labrador tea.13H x 13W. Showy white flowers inlate spring, tolerates wet feet.IV: Ilex verticillata, winterberry. 68H x68W. Plant a male and female to takeadvantage of showy orange berries thatpersist all winter long.Perennials:**RF: Osmunda regalis, royal fern. 25H x25W. Large, showy fern. Needsmoisture! You must keep this plantwatered if you are experiencing lowrainfall.C: Aquilegia canadensis, native colombine.12H x 12W. Showy red and yellowflowers in spring. Sometimes bloomsagain in autumn. Beautiful foliage.S: Onoclea sensibilis, sensitive fern. 2H x18W. Soft, green fern. Thrives in moistareas.CA: Lobelia cardinalis, cardinal flower. 24Hx 1W. Bright red flowers from July toSeptember.Plants for the dryer outer edge ofthe garden:Woody shrubs:*W: Comptonia peregrina, sweetfern. 24Hx 24W. Rickrack-shaped leaves areheavily scented when crushed. Comptoniashould be purchased in sod form as it isdifficult to establish individual plants.Tolerates sandy, dry, rocky soil.AR: Arctostaphylos uva-ursi, bearberry.612H x 1-2W. Shiny evergreen leavesturn bronze in the fall. Small white to pinkflowers in the early spring, bright redberries in late summer that persist throughwinter. Tolerates sandy, dry, rocky soil.PHOTO: EDWIN REMSBERG, USDA-CSREESPerennials:**G: Geranium maculatum, wild geranium. 12H x 2W or more. Purple flowers in the late spring and sometimes again in the fall. Pretty foliage.*Woody shrubs: Though they may shedtheir leaves, the woody structure of the plantwill provide winter interest in the garden.**Perennials: These plants die over thewinter and sprout new shoots in the spring.Sometimes some of last years foliage willsurvive the winter, but generally you shouldtrim off the dead foliage in late fall and waitfor the green growth of spring. ADDING A RAIN GARDEN TO YOUR LANDSCAPE, BULLETIN #2702 7 8. ResourcesNative plant lists from the Portland Water District and the MaineDeveloped by UMaine ExtensionDepartment of Environmental Protection: part of the Conservation Assistant Scientist Laura WilsonPractices for Homeowners fact sheet series. Available at and Water Resource Specialist Gilbertson of the PortlandNative Plant List; Part/Full Shade, Dry Soil, DEPLW0777, May Water District, with landscape 2006. diagrams by Kirsten Reberg-Horton.Native Plant List; Part/Full Sun, Dry Soil, DEPLW0778, May 2006. Editor: Kyle McCaskillNative Plant List; Part/Full Shade, Moist to Wet Soils, DEPLW0776, Design: Cindy Eves-Thomas May 2006.Native Plant List; Part/Full Sun, Moist to Wet Soils, DEPLW0779, May 2006. www.umext.maine.eduLandscapes for Maine bulletins from UMaine Cooperative Extension.A Member of the University of Maine SystemAvailable at or by calling 800-287-0274Published and distributed in furtherance of Acts of(in Maine): Congress of May 8 and June 30, 1914, by the University of Maine Cooperative Extension, the LandDesigning Your Landscape for Maine, bulletin #2701 (Orono, ME: Grant University of the state of Maine and the U.S. Department of Agriculture cooperating. Cooperative2005). Extension and other agencies of the U.S.D.A.Gardening to Conserve Maines Native Landscape: Plants to Use andprovide equal opportunities in programs and employment. 11/06Plants to Avoid, bulletin #2500 (Orono, ME: 2003). Produced by the UMaine CooperativeNative Plants: A 2002 Maine Source List, bulletin #2502 (Orono,Extension Communications Office.ME: 2002).The Buffer Handbook Plant List, Cynthia Kuhns for the Maine This material is based upon Department of Environmental Protection. DEPLW0094-A2001,work supported by the 1998, Revised 2001. Available at State Research, blwq/docwatershed/bufhand.htm.Education, and Extension Service, U.S. Department ofNeed an expert?Agriculture, under agreement nos. 2003-51130-02074 andIn Central or Northern Maine:2004-51130-03108, through the CSREESLaura Wilson, Extension Assistant ScientistNew England Regional Water QualityUniversity of Maine Cooperative ExtensionProgram.495 College AvenueOrono, ME 04473-1294207-581-2971 or lwilson@umext.maine.eduIn Southern Maine:Mary Gilbertson, Water Resource SpecialistPortland Water District1 White Rock RoadStandish, ME 04084207-774-5961 x3336 or mgilbertson@pwd.orgReferencesBannerman, R., E. Considine, and J. Horwatich. Rain Gardens: A How- To Manual for Homeowners. UWEX Publications GWQ037. University of Wisconsin-Extension, 2003.Dietz, M. E. and J. C. Clausen. A Field Evaluation of Rain Garden Flow and Pollutant Treatment. Water, Air, and Soil Pollution 167 (October 2005): 123128.Wilson, G. Burnsville Rainwater Gardens. Land and Water 48, no. 58 UNIVERSITY OF MAINE COOPERATIVE EXTENSION


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