Download - Maine: Adding a Rain Garden to Your Landscape

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A rain garden is a depressionin the ground that is planted withwater-loving native perennials andshrubs. Water from a downspoutor other source flows into the raingarden, where it soaks into theground and is used by the plants.

Rain gardens make senseRain gardens help protect the

water quality in our lakes, streams,and rivers by reducing the amountof polluted runoff reaching theseresources. If designed and installedcorrectly, rain gardens reduce theamount of runoff from hard,impervious surfaces by up to 98percent. As this water is no

longer running over the surfaceof the land, it cannot transportpollutants to nearby streams viasurface runoff or storm drains.

Rain gardens are easy andinexpensive to install andmaintain. Since they are flexiblein size, shape, and appearance,they can fit into almost anylandscape and lifestyle.

Rain gardens are beautifulIn addition to adding beauty

to lawn areas with height andcolor, rain gardens can replacelawn areas, which wouldotherwise need mowing, with aninteresting combination of nativeplants. Rain gardens can alsoeliminate unsightly erosionproblems on your property byreducing excess water fromrooftops or driveways. They can

complement any home style, asthere are many choices of shapesand plants that can beincorporated into your garden.Rain gardens can even attractbirds and butterflies!

PPllaannnniinngg ffoorr YYoouurr RRaaiinnGGaarrddeennChoose a location

Follow these placementguidelines to help make the raingarden more enjoyable for youand your neighbors:

� Remember that the purposeof the rain garden is to putwater into the ground! Placeyour garden at least ten feet

Adding a Rain Garden to Your Landscape

Bulletin #2702

Landscapes for Maine

Pollutant Removal Mechanism Pollutants Removed

Absorption to soil particles Dissolved metals and soluble phosphorusSmall amounts of nutrients including phosphorusand nitrogen

Microbial processes Organics, pathogens

Exposure to sunlight and dryness Pathogens

Infiltration of runoff Minor abatement of localized flooding, minorincrease in localized base flow of groundwater,allowing some nutrients to be removed whengroundwater flows through buffer

Sedimentation and filtration Total suspended solids, floating debris, trash, soil-bound phosporus, some soil-bound pathogens

Do rain gardens harbor

mosquitoes?

A properly constructed rain gardenwill drain water, not hold it. In awell-designed rain garden, waterwill soak into the ground in a day.Mosquitoes will not survive inareas that dry out in seven daysor less after a summer rain,because the development of amosquito from egg to adult takeslonger than seven days.

How rain gardens remove pollutants

Brix, H. "Wastewater treatment in constructed wetlands system design, removal processes, and treatmentperformance." In Constructed Wetlands for Water Quality Improvement, ed. G.A. Moshiri, 9–22. Boca Raton, Fl:CRC Press, 1993. Adapted in W. Hunt and N. White, Designing Rain Gardens. NC State University CooperativeExtension, 2001. http://www.engr.uga.edu/service/outreach/Stormwater%20BMP/BioretentionOverview.pdf

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2 UNIVERSITY OF MAINE COOPERATIVE EXTENSION

away from your foundationin order to avoid waterseepage in your basement.

� Do not place a rain gardenover a septic tank or leachfield.

� Do not place a rain gardennear your drinking water well.

� Be aware of and avoidunderground pipes andutilities. If you don’t knowwhere they are, call Dig Safe®at 1-888-DIG-SAFE (344-7233)at least three days beforedigging. Outline the proposedarea with white paint. DigSafe® will automatically notifyall of its member utilities(gas/oil/steam, electric,communications, water, andsewer) that own undergroundfacilities in the area of theexcavation so that they canmark their facilities.

� Check for any private wiringor underground utilities.Look around for lights in theyard, such as spotlights onflagpoles or signs, lights atthe end of the driveway, andsheds with electricity.

� Place the rain garden in a flatarea if possible to makeinstallation easier.

� Do not place the rain gardenin a naturally wet area. Wetspots may seem ideal, butthey will drain too slowly.

� Avoid trees and tree roots, asthey may be injured by nearbydigging and may not tolerateadditional moisture in the soil.

� Maine has mandatoryprotective Shoreland Zoningregulations. If you are working

on lakefront, stream front, orcoastal property, contact yourlocal code enforcement officerbefore you begin. If you livein Maine’s unorganizedterritory, contact the LandUse Regulation Commission(LURC) at 207-287-2631.

Determine how big yourrain garden should be

For best water qualitytreatment benefits, the rain gardenshould hold the water from aone-inch rainstorm. An easy wayto ensure this is to make the raingarden 30 percent of the drainagearea. To calculate that volume,figure out the size of the rooftop,driveway, or other impervioussurface that will drain into yourgarden in square feet, and makethe garden area 30 percent of thatarea. For example, a 1000-square-foot rooftop would require a 300-square-foot rain garden.

You can make the rain gardenlarger than 30 percent of thedrainage area, or as small as 20percent. Simply use 30 percent asa guideline.

Decide how to channel thewater

How you direct water from thedownspout, driveway, or otherhard surface to the rain garden isa matter of choice. Some commonmethods include gutter extensions,piping, and ditches.

Gutter extensions are simplymetal gutter pipes attached to theends of your downspouts. Theymust be angled downwardslightly for the water to flow. Theadvantage of gutter extensions isthat they are easy to install.However, some people find them

unsightly. You may prefer tocarry your water undergroundvia plastic or PVC pipe.

Grass-lined shallow ditches,or swales, can be used to directwater to the rain garden. Theseditches should be gently slopedto avoid erosion. The side slopesof the ditch should be no steeperthan a 2:1 ratio (a one-foot rise forevery two feet across).

If you expect heavy flows ofwater (e.g. from a large drivewayarea), a rock-lined ditch isadvisable. Line the ditch withlandscape fabric in order toprevent it from eroding.

Stabilize the area where thewater enters your rain gardenwith stone to prevent erosion ofthe rain garden. Watch this areacarefully during the first fewrainstorms following installation.

I have a lot of standing water

on my property. Can I still have

a rain garden?

Rain gardens are designed toinfiltrate water. Standing waterindicates poor infiltration, and wedo not recommend directingadditional water to these naturallywet areas.

Plan ahead for grassremoval

If the rain garden is located inan existing lawn, you may wantto kill the grass before digging.This takes some forethought, asyou will need to lay black plasticor a tarp on the lawn until thegrass dies (doing this over thewinter works best).

Do NOT use a weed killer suchas Roundup® to kill grass. Youcan always simply remove thesod as you excavate the garden,and use it elsewhere if possible.

Estimate your costThe cost will depend on how

much work you decide to doyourself. If you do all of the work—digging the garden, buying theplants, planting, and mulching—your costs will range from three tofive dollars a square foot. If youhire a landscaper to do some ormost of the work, such as designwork, excavation, or planting, thetotal cost could approach ten tofifteen dollars a square foot.

DDeessiiggnniinngg YYoouurr RRaaiinnGGaarrddeennDetermine shape andplacement

Once you have calculated thesize of your rain garden, determinea general shape, and position thegarden within your landscape.Have fun, and explore two orthree options before making afinal design decision.

Rain gardens can be circular,kidney-shaped, or long andnarrow. The shape of the gardendepends on your wants andneeds. Just remember that a

central portion of the gardenmust be six inches below thegrade of the surrounding land inorder to temporarily hold water.Gently slope the garden to thislowest point to avoid erosionwithin the garden. A one-inchdrop for every foot across is agood rule of thumb. For a 300-square-foot rain garden, choicesinclude a circular garden with a20 foot diameter, or a longer,narrower garden approximately10 feet by 30 feet.

Remember that rain gardenson slopes will need to be dugmore deeply into the high side ofthe slope to produce a levelbottom. You will need to build aberm, or hump, on the lower endto keep the water in the garden.

The design stage provides anopportunity to get creative. Whilethinking about the shape of thegarden as well as the color, shape,and height of the plants, consideradding elements such as stone orfencing, or set a bench nearby.Personalize your garden!

Select plants for yourdesign

When selecting plants, consider

• zone hardiness,• sunlight needs,• moisture needs,• soil type needs,• height and width,• color,• texture, and• whether they are native.

Is your site shady or sunny?Remember that it takes more thansix hours of sunlight to beconsidered “full sun.” Chooseplants that will perform well inthe light you have available.Choose water-loving plants for

the lowest portion of the raingarden, and dry-tolerant plantsfor the edges.

Use native plants wheneverpossible. Native plants willsurvive better in our environment.For help selecting native plantsthat meet your light, moisture,and height requirements, consultour bulletin #2500, Gardening toConserve Maine’s Native Landscape.This bulletin specifies the lightand moisture needs and eventualheight of native perennials and

ADDING A RAIN GARDEN TO YOUR LANDSCAPE, BULLETIN #2702 3

Buying your plants

Buy plants with healthy rootsystems. The healthier the rootsystem, the quicker your plants willbecome established. Use onlynursery-propagated plants orthose from your own garden. DONOT collect plants from the wild. Ifyou buy bare-root perennials, besure to keep the roots moist untilyou plant them.

“Plugs” will get you more plantsfor less money. These small-sized seedlings grown in traystake longer to fill in the space inyour garden, but plugs can helpkeep costs down.

Most reputable nurseries haveselections of native plants. If youare unsure, ask nursery staff! Theyare very knowledgeable, and willoften have other suggestions if aparticular plant is not available.Also, asking for native plants mayconvince nurseries to offer more ofthem. For sources of native plants,consult our bulletin #2502, NativePlants: A 2002 Maine Source List(see Resources section).

Plan ahead. Nurseries will have alarger selection in the spring thanat the end of the summer. Youmay have to visit multiplenurseries if you want a largenumber of a particular plant.

shrubs. Plants designated “H”(hydric) will do well in the lowest,wettest areas of the rain garden,while “M” (mesic) to “S” (sub-xeric) will do well in the drier areas.

Another good resource is TheBuffer Handbook Plant List, whichindicates whether plants will dowell in wet, moist, or dryconditions, and includes native aswell as noninvasive, nonnativeplants. (See Resources section forboth publications.)

IInnssttaalllliinngg YYoouurr RRaaiinnGGaarrddeennAvoid wet conditions

Be sure to install your raingarden when the soil is dry. If youdisturb wet soils, you compactthe soil to the point that watercan no longer infiltrate—whichwill defeat the entire purpose of arain garden!

Dig your garden

Once you know the size, shape,and location of the rain garden,it’s time to get your hands dirty!If you do all the work yourself, itmay take the better part of a day.Consider inviting friends to makethe work faster and more fun.

First, delineate the outline ofthe rain garden on the ground. Youcan use a garden hose, string, orspray paint. Be flexible. Even themost carefully sketched plan mayneed to be adjusted to fit the area.

If you have not already killedthe grass in your garden area witha black plastic or other covering,you will need to remove the sodas you excavate the garden. DoNOT use a weed killer such asRoundup® to kill the grass.

Try not to compact the soil asyou dig the rain garden. Workfrom one side to the other side, orfrom the center to the outside, soyou don’t pack down the soil.

Loosen the soil at least twofeet deep. Even though the gardenwill only be six inches deep in thecenter, loosening the soil will helpyour plants establish root systemsin this new environment. Now isthe time to add compost or othersoil amendments if needed.

Use extra soil to create a bermon the downslope side of thegarden. The berm will act as awall to hold water in the gardenduring storms. Make the bermthree to six inches high and eightto twelve inches wide, with gentlysloping sides. Taper it off as itwraps around to the inlet of therain garden. Now stomp on it!This soil needs to be compactedto hold the water in the gardenbefore it soaks into the ground.

Cover the berm with grass ormulch to prevent erosion. If youseed the berm, use straw toprevent it from eroding until thegrass takes hold.

Plant your rain gardenThis is the fun part!Set your plants out in the

garden to match your design. Nowyou can adjust the position of theplants, if necessary, before youstart planting. If possible, keepthe plants in their pots to preventthem from drying out before theyare planted. Wrap bare-root plantsin wet newspaper until planting.

Remember that you don’t wantto compact the soil. Work fromone side of the garden to the otherto reduce the amount of foot trafficin the garden. If you think thatyou have packed the soil downtoo much, use a rake to loosen it.

Dig each hole twice as wide asthe pot and deep enough to keepthe crown of the plant level withthe ground. Make sure your plantis level, then fill the hole with soiland pack the soil around theplant to remove any air pockets.

Water immediately afterplanting. Giving the plants a goodsoaking will give your rain gardena good start. Use a watering can ifpossible: a high-pressure blastfrom a hose will push soil awayfrom the plant and keep the waterfrom soaking in, doing more harmthan good. Water the new plantsbefore adding mulch to ensurethat the maximum amount ofwater reaches the roots.

Mulch your garden


Soil mix matters

The rain garden should allowwater to easily seep into theground. If your soil is mostly clay,you may need to amend the soilto make it more permeable. Arecommended soil mix is 50 to60 percent sand, using native soilfor the remainder. Adding up to20 percent compost in place ofnative soil will enhance initialplant growth, and high-clay soilswill need even higher amounts ofcompost, organic matter, or topsoilto increase soil permeability.

The value of mulch is oftenoverlooked. Mulch is importantin any garden to keep plantsmoist and discourage weeds.Layering sheets of newspaperaround the plants before addingmulch will provide an addedweed barrier.

Apply a three- to four- inchlayer of mulch to your rain garden.Be sure to keep the mulch awayfrom the crown of each plant.Add some additional mulch eachyear for a few years, until theplants have matured, so the soildoes not dry out too quickly.After a few years, mulch is notnecessary, unless you prefer itsmore formal appearance.

How much mulch will youneed? A cubic yard1 of mulch willcover a 100-square-foot area withabout three inches of mulch.

With the exception of barkchips and artificially coloredmulches, you can generally useany type of mulch that will stayin place and retain moisture. Barkchips don’t work because theytend to float away in rain gardens,and artificially colored mulch willleach color into the soil. We haveused Superhumus and ErosionControl Mix—blended productsfrom earthlife™—in our test raingardens with success. If you areunsure, ask your nurseryprofessional.

Nurseries sell mulch by thebag and by the cubic yard. If youdon’t have access to a truck, mostnurseries will deliver for anominal fee.

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Watch your rain garden thefirst time it rains. Where does thewater go? Does it pond whereyou intended it to? Or are themoisture-loving plants left highand dry? Does the force of thewater erode the mulch and soil atthe entrance to the rain garden?Use the first few storms to evaluateyour garden. If the contours needto be adjusted, use a rake orshovel as needed. Strategicallyplaced rocks can slow the force ofthe water.

If you have used shallowditches or swales to direct waterto the rain garden, inspect theseditches often to be sure that thebottoms are not eroding. Keepingthe side slopes of the ditches nosteeper than 2:1 (for every twofeet across, a one-foot rise) willhelp prevent erosion.

Keep in mind that during thefirst year, especially during thedry summer months, you mayneed to water the rain garden sothat the plants can get established.Use a rain gauge to keep track ofthe rainfall. Your rain garden willneed one to two inches of waterper week the first year.

Frequent weeding will benecessary in the first few yearsbefore plants become established.In order to distinguish betweenweeds and young plants, consideradding plant labels next to eachplant.

Once the plants mature andbecome established, maintenanceof a rain garden is nothing morethan routine landscape

maintenance: weeding, pruning,plant replacement, mulching, andsupplemental watering duringdry spells.

While some people trim deadstems and leaves from theirperennials before winter, you canleave them over the winter toprovide food for birds and wildlife.Once new growth appears in thespring, remove the dead stemsand leaves.

Solving plant problemsHere are some considerations

if your rain garden plants fail tothrive:

� New plants need a consistentsupply of water until theirroots are established—eventhough your rain gardencatches stormwater. Your raingarden will need one to twoinches of water per weekduring the first year.

� Consider the location of eachplant within the garden.Some plants will not toleratehaving their roots dry out,while others do not like themto be moist all the time.

� Double-check the hardinesszone rating of your plants. Ifyou end up replacing plants,choose plants rated for acolder zone than yours, toensure that they can survivethe very coldest temperaturesthey might experience.

� Make sure that you haveused plants well suited to thelight levels and light durationof your garden’s location.


1 27 cubic feet, or about what will fit inthe back of a pickup truck


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Rain Garden

Plants for the wetter center of thegarden:

Woody shrubs:*

SS: Clethra alnifolia, summersweet. 5–6’H x4–6’W. Late-to-emerge foliage. Fragrant,large, white flower stalks in summer.

Perennials:**

CA: Lobelia cardinalis, cardinal flower. 2–4’Hx 1’W. Bright red flowers from July toSeptember.

T: Asclepias tuberose, orange butterflyweed. 2–3’H x 2–3’W. Can handle dryareas. Orange blooms from June toSeptember.

I: Iris versicolor, blue flag iris. 2–4’H x2–4’W. Blue flowers in spring.

M: Caltha palustris, marsh marigold. 8”H x1’W. Glossy heart-shaped leaves withbright yellow flowers in the spring.

J: Eupatorium maculatum, joe-pye weed.3–5’H x 1–2’W. Red stems, purple-redflowers from July to September.

SM: Asclepias incarnate, swamp milkweed.2–3’H x 2–3’W. 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. 1–3’H x1–3’W. Thick leaves and many whiteflowers all summer.

Perennials:**

G: Geranium maculatum, wild geranium.1–2’H x 2’W or more. Purple flowers inthe late spring and sometimes again inthe fall. Pretty foliage.

A: Anemone canadensis, windflower. 2’H x10”W. Pure white blossoms in June.Large, attractive leaves.

LO: Lobelia spicata, spiked lobelia. 3–5’H x3–5’W. Blue flowers from June toAugust.

FA: Symphyotrichum umbellatus, flat-toppedaster. 3–7’H x 3–7’W. White toyellowish-centered flowers in the fall.

AS: Symphyotrichum novae-angliae, NewEngland aster. 3–7’H x 3–7’W. Purpleflowers in the fall.

H: Helenium autumnale, perennialsunflower, 3–5’H x 2–3’W. 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 year’s foliage willsurvive the winter, but generally you shouldtrim off the dead foliage in late fall and waitfor the green growth of spring.


EExxaammppllee ooff aa SShhaaddyy RRaaiinn GGaarrddeenn DDeessiiggnnPlant List for a Shady

Rain Garden

Plants for the wetter, shadiercenter of the garden:

Woody shrubs:*

HV: Hamamelis vernalis, vernal witch hazel.6–10’H x 6–10’W. Showy golden yellowfall color. Long-lasting, scented yellowflowers in the late winter.

RH: Rhododendron canadense, rhodora(native rhododendron). 1–3’H x 1–3’W.Showy purple flowers in the spring.Tolerates wet, acidic soil.

LE: Ledum groenlandicum, Labrador tea.1–3’H x 1–3’W. Showy white flowers inlate spring, tolerates wet feet.

IV: Ilex verticillata, winterberry. 6–8’H x6–8’W. Plant a male and female to takeadvantage of showy orange berries thatpersist all winter long.

Perennials:**

RF: Osmunda regalis, royal fern. 2–5’H x2–5’W. Large, showy fern. Needsmoisture! You must keep this plantwatered if you are experiencing lowrainfall.

C: Aquilegia canadensis, native colombine.1–2’H x 1–2’W. Showy red and yellowflowers in spring. Sometimes bloomsagain in autumn. Beautiful foliage.

S: Onoclea sensibilis, sensitive fern. 2'H x18”W. Soft, green fern. Thrives in moistareas.

CA: Lobelia cardinalis, cardinal flower. 2–4’Hx 1’W. Bright red flowers from July toSeptember.

Plants for the dryer outer edge ofthe garden:

Woody shrubs:*

W: Comptonia peregrina, sweetfern. 2–4’Hx 2–4’W. 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.6–12”H 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.

Perennials:**

G: Geranium maculatum, wild geranium.1–2’H x 2’W or more. Purple flowers inthe late spring and sometimes again inthe 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 year’s foliage willsurvive the winter, but generally you shouldtrim off the dead foliage in late fall and waitfor the green growth of spring.

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RReessoouurrcceessNative plant lists from the Portland Water District and the MaineDepartment of Environmental Protection: part of the ConservationPractices for Homeowners fact sheet series. Available athttp://www.pwd.org/news/publications.php.

Native Plant List; Part/Full Shade, Dry Soil, DEPLW0777, May2006.

Native Plant List; Part/Full Sun, Dry Soil, DEPLW0778, May 2006.Native Plant List; Part/Full Shade, Moist to Wet Soils, DEPLW0776,

May 2006.Native Plant List; Part/Full Sun, Moist to Wet Soils, DEPLW0779,

May 2006.

Landscapes for Maine bulletins from UMaine Cooperative Extension.Available at www.umext.maine.edu or by calling 800-287-0274(in Maine):

Designing Your Landscape for Maine, bulletin #2701 (Orono, ME:2005).

Gardening to Conserve Maine’s Native Landscape: Plants to Use andPlants to Avoid, bulletin #2500 (Orono, ME: 2003).

Native Plants: A 2002 Maine Source List, bulletin #2502 (Orono,ME: 2002).

The Buffer Handbook Plant List, Cynthia Kuhns for the MaineDepartment of Environmental Protection. DEPLW0094-A2001,1998, Revised 2001. Available at http://www.maine.gov/dep/blwq/docwatershed/bufhand.htm.

Need an expert?In Central or Northern Maine:Laura Wilson, Extension Assistant ScientistUniversity of Maine Cooperative Extension495 College AvenueOrono, ME 04473-1294207-581-2971 or [email protected] Southern Maine:Mary Gilbertson, Water Resource SpecialistPortland Water District1 White Rock RoadStandish, ME 04084207-774-5961 x3336 or [email protected]

RReeffeerreenncceessBannerman, 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 GardenFlow and Pollutant Treatment.” Water, Air, and Soil Pollution 167(October 2005): 123–128.

Wilson, G. “Burnsville Rainwater Gardens.” Land and Water 48, no. 5

Developed by UMaine ExtensionAssistant Scientist Laura Wilsonand Water Resource SpecialistMary Gilbertson of the PortlandWater District, with landscapediagrams by Kirsten Reberg-Horton.

Editor: Kyle McCaskillDesign: Cindy Eves-Thomas

www.umext.maine.edu

A Member of the University of Maine SystemPublished and distributed in furtherance of Acts ofCongress of May 8 and June 30, 1914, by theUniversity of Maine Cooperative Extension, the LandGrant University of the state of Maine and the U.S.Department of Agriculture cooperating. CooperativeExtension and other agencies of the U.S.D.A.provide equal opportunities in programs andemployment. 11/06

Produced by the UMaine CooperativeExtension Communications Office.

This material is based upon

work supported by the

Cooperative State Research,

Education, and Extension

Service, U.S. Department of

Agriculture, under agreement

nos. 2003-51130-02074 and

2004-51130-03108, through the CSREES

New England Regional Water Quality

Program.

Download - Maine: Adding a Rain Garden to Your Landscape

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