Maine: Adding a Rain Garden to Your Landscape


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Maine: Adding a Rain Garden to Your Landscape

  1. 1. Landscapes for Maine PHOTO: EDWIN REMSBERG, USDA-CSREES Adding a Rain Garden to Your LandscapeBulletin #2702What Is a Rain Garden longer running over the surface of the land, it cannot transport complement any home style, as there are many choices of shapesand Why Would You pollutants to nearby streams via and plants that can be surface runoff or storm drains. incorporated into your garden.Want One? Rain gardens are easy and Rain gardens can even attract A rain garden is a depression inexpensive to install and birds 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 any mosquitoes?or other source flows into the rain landscape and lifestyle. A properly constructed rain gardengarden, where it soaks into the Rain gardens are beautiful will drain water, not hold it. In aground and is used by the plants. well-designed rain garden, water In addition to adding beauty will soak into the ground in a day.Rain gardens make sense to lawn areas with height and Mosquitoes will not survive in color, rain gardens can replace areas that dry out in seven days Rain gardens help protect the or less after a summer rain,water quality in our lakes, streams, lawn areas, which would because the development of aand rivers by reducing the amount otherwise need mowing, with an mosquito from egg to adult takesof polluted runoff reaching these interesting 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 by Planning 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 pollutants Follow these placementPollutant Removal Mechanism Pollutants Removed guidelines to help make the rainAbsorption to soil particles Dissolved metals and soluble phosphorus garden more enjoyable for you Small amounts of nutrients including phosphorus and your neighbors: and nitrogenMicrobial processes Organics, pathogens Remember that the purposeExposure to sunlight and dryness Pathogens of the rain garden is to put water into the ground! PlaceInfiltration of runoff Minor abatement of localized flooding, minor increase in localized base flow of groundwater, your garden at least ten feet allowing some nutrients to be removed when groundwater flows through bufferSedimentation and filtration Total 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, 9–22. Boca Raton, Fl:CRC Press, 1993. Adapted in W. Hunt and N. White, Designing Rain Gardens. NC State University CooperativeExtension, 2001.
  2. 2. away from your foundation on lakefront, stream front, or unsightly. You may prefer to in order to avoid water coastal property, contact your carry your water underground seepage in your basement. local code enforcement officer via plastic or PVC pipe. before you begin. If you live Grass-lined shallow ditches, Do not place a rain garden in Maine’s unorganized or swales, can be used to direct over a septic tank or leach territory, contact the Land water to the rain garden. These field. Use Regulation Commission ditches should be gently sloped Do not place a rain garden (LURC) at 207-287-2631. to avoid erosion. The side slopes near your drinking water well. of the ditch should be no steeper Determine how big your than a 2:1 ratio (a one-foot rise for Be aware of and avoid rain garden should be underground pipes and every two feet across). utilities. If you don’t know For best water quality If you expect heavy flows of where they are, call Dig Safe® treatment benefits, the rain garden water (e.g. from a large driveway at 1-888-DIG-SAFE (344-7233) should hold the water from a area), a rock-lined ditch is at least three days before one-inch rainstorm. An easy way advisable. Line the ditch with digging. Outline the proposed to ensure this is to make the rain landscape fabric in order to area with white paint. Dig garden 30 percent of the drainage prevent it from eroding. Safe® will automatically notify area. To calculate that volume, Stabilize the area where the all of its member utilities figure out the size of the rooftop, water enters your rain garden (gas/oil/steam, electric, driveway, or other impervious with stone to prevent erosion of communications, water, and surface that will drain into your the rain garden. Watch this area sewer) that own underground garden in square feet, and make carefully during the first few facilities in the area of the the garden area 30 percent of that rainstorms following installation. excavation so that they can area. 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 garden I have a lot of standing water or underground utilities. larger than 30 percent of the on my property. Can I still have Look around for lights in the drainage area, or as small as 20 a rain garden? yard, such as spotlights on percent. Simply use 30 percent as Rain gardens are designed to flagpoles or signs, lights at a guideline. infiltrate water. Standing water the end of the driveway, and indicates poor infiltration, and we sheds with electricity. Decide how to channel the do not recommend directing Place the rain garden in a flat water additional water to these naturally wet areas. area if possible to make How you direct water from the installation easier. downspout, driveway, or other Do not place the rain garden hard surface to the rain garden is in a naturally wet area. Wet a matter of choice. Some common spots may seem ideal, but methods include gutter extensions, they will drain too slowly. piping, and ditches. Gutter extensions are simply Avoid trees and tree roots, as metal gutter pipes attached to the they may be injured by nearby ends of your downspouts. They digging and may not tolerate must be angled downward additional moisture in the soil. slightly for the water to flow. The Maine has mandatory advantage of gutter extensions is protective Shoreland Zoning that they are easy to install. regulations. If you are working However, some people find them2 UNIVERSITY OF MAINE COOPERATIVE EXTENSION
  3. 3. Plan ahead for grass central portion of the garden the lowest portion of the rainremoval must be six inches below the garden, and dry-tolerant plants grade of the surrounding land in for 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, as within 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 the good rule of thumb. For a 300- and height requirements, consultgrass dies (doing this over the square-foot rain garden, choices our bulletin #2500, Gardening towinter works best). include a circular garden with a Conserve Maine’s Native Landscape. Do NOT use a weed killer such 20 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 level Buying 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 an become established. Use onlyplants, planting, and mulching— opportunity to get creative. While nursery-propagated plants oryour costs will range from three to thinking 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 or you buy bare-root perennials, be and height of the plants, consider sure to keep the roots moist untilmost of the work, such as design adding elements such as stone or you 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 your take longer to fill in the space inDesigning Your Rain design your garden, but plugs can help keep costs down.Garden When 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 a Once you have calculated the particular plant is not available. • height and width,size of your rain garden, determine Also, asking for native plants may • color,a general shape, and position the convince 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 a Is your site shady or sunny? (see Resources section).final design decision. Remember that it takes more than Rain 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 garden plants that will perform well in may have to visit multipledepends on your wants and the light you have available. nurseries if you want a largeneeds. Just remember that a Choose water-loving plants for number of a particular plant. ADDING A RAIN GARDEN TO YOUR LANDSCAPE, BULLETIN #2702 3
  4. 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, it’s time to get your hands dirty! seed the berm, use straw towhile “M” (mesic) to “S” (sub- If you do all the work yourself, it prevent 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, which the work faster and more fun. Plant your rain gardenindicates whether plants will do First, delineate the outline of This is the fun part!well in wet, moist, or dry the rain garden on the ground. You Set your plants out in theconditions, and includes native as can use a garden hose, string, or garden 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, keep If you have not already killed the 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 sod in wet newspaper until planting. as you excavate the garden. Do Remember that you don’t wantAvoid wet conditions NOT use a weed killer such as to compact the soil. Work from Be sure to install your rain Roundup® to kill the grass. one side of the garden to the othergarden when the soil is dry. If you Try not to compact the soil as to reduce the amount of foot trafficdisturb wet soils, you compact you dig the rain garden. Work in the garden. If you think thatthe soil to the point that water from one side to the other side, or you have packed the soil downcan no longer infiltrate—which from the center to the outside, so too much, use a rake to loosen it.will defeat the entire purpose of a you don’t pack down the soil. Dig each hole twice as wide asrain garden! Loosen the soil at least two the pot and deep enough to keep feet deep. Even though the garden the crown of the plant level withDig your garden will only be six inches deep in the the ground. Make sure your plant center, loosening the soil will help is level, then fill the hole with soil Soil mix matters your plants establish root systems and pack the soil around the The rain garden should allow in this new environment. Now is plant to remove any air pockets. water to easily seep into the the time to add compost or other Water immediately after ground. If your soil is mostly clay, soil amendments if needed. planting. Giving the plants a good you may need to amend the soil Use extra soil to create a berm soaking will give your rain garden to make it more permeable. A on the downslope side of the a good start. Use a watering can if recommended soil mix is 50 to 60 percent sand, using native soil garden. The berm will act as a possible: a high-pressure blast for the remainder. Adding up to wall to hold water in the garden from a hose will push soil away 20 percent compost in place of during storms. Make the berm from the plant and keep the water native soil will enhance initial three to six inches high and eight plant growth, and high-clay soils from soaking in, doing more harm will need even higher amounts of to twelve inches wide, with gently than good. Water the new plants compost, organic matter, or topsoil sloping sides. Taper it off as it before adding mulch to ensure to 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 garden Mulch your garden before it soaks into the ground.4 UNIVERSITY OF MAINE COOPERATIVE EXTENSION
  5. 5. The value of mulch is oftenoverlooked. Mulch is important Maintaining Your Rain maintenance: weeding, pruning, plant replacement, mulching, andin any garden to keep plants Garden supplemental watering duringmoist and discourage weeds. dry spells.Layering sheets of newspaper Watch your rain garden the While some people trim deadaround the plants before adding first time it rains. Where does the stems and leaves from theirmulch will provide an added water go? Does it pond where perennials before winter, you canweed barrier. you intended it to? Or are the leave them over the winter to Apply 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 at spring, 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 the your garden. If the contours need Solving plant problemsplants have matured, so the soil to be adjusted, use a rake or Here are some considerationsdoes not dry out too quickly. shovel as needed. Strategically if your rain garden plants fail toAfter a few years, mulch is not placed rocks can slow the force of thrive:necessary, unless you prefer its the water.more formal appearance. If you have used shallow New plants need a consistent How much mulch will you ditches or swales to direct water supply of water until theirneed? A cubic yard1 of mulch will to the rain garden, inspect these roots are established—evencover a 100-square-foot area with ditches often to be sure that the though your rain gardenabout three inches of mulch. bottoms are not eroding. Keeping catches stormwater. Your rain With the exception of bark the side slopes of the ditches no garden will need one to twochips and artificially colored steeper than 2:1 (for every two inches 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. Bark Keep in mind that during the plant within the garden.chips don’t work because they first year, especially during the Some plants will not toleratetend to float away in rain gardens, dry summer months, you may having their roots dry out,and artificially colored mulch will need 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 Erosion Use a rain gauge to keep track of the rainfall. Your rain garden will Double-check the hardinessControl Mix—blended products need one to two inches of water zone rating of your plants. Iffrom earthlife™—in our test rain per week the first year. you end up replacing plants,gardens with success. If you are Frequent weeding will be choose 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 survive Nurseries sell mulch by the In order to distinguish between the very coldest temperaturesbag and by the cubic yard. If you weeds and young plants, consider they might experience.don’t 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 the Once the plants mature and light levels and light duration become established, maintenance of your garden’s location. of a rain garden is nothing more than routine landscape1 27 cubic feet, or about what will fit inthe back of a pickup truck ADDING A RAIN GARDEN TO YOUR LANDSCAPE, BULLETIN #2702 5
  6. 6. Example of a Sunny Rain Garden Design Plant List for a Sunny Rain Garden Plants for the wetter center of the garden: Woody shrubs:* SS: Clethra alnifolia, summersweet. 5–6’H x 4–6’W. Late-to-emerge foliage. Fragrant, large, white flower stalks in summer. Perennials:** CA: Lobelia cardinalis, cardinal flower. 2–4’H x 1’W. Bright red flowers from July to September. T: Asclepias tuberose, orange butterfly weed. 2–3’H x 2–3’W. Can handle dry areas. Orange blooms from June to September. I: Iris versicolor, blue flag iris. 2–4’H x 2–4’W. Blue flowers in spring. M: Caltha palustris, marsh marigold. 8”H x 1’W. Glossy heart-shaped leaves with bright yellow flowers in the spring. J: Eupatorium maculatum, joe-pye weed. 3–5’H x 1–2’W. Red stems, purple-red flowers 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 to October. Plants for the dryer outer edge of the garden: Woody shrubs:* P: Potentilla arguta, tall cinquefoil. 1–3’H x 1–3’W. Thick leaves and many white flowers all summer. Perennials:** G: Geranium maculatum, wild geranium. 1–2’H x 2’W or more. Purple flowers in the late spring and sometimes again in the fall. Pretty foliage. A: Anemone canadensis, windflower. 2’H x 10”W. Pure white blossoms in June. Large, attractive leaves. LO: Lobelia spicata, spiked lobelia. 3–5’H x 3–5’W. Blue flowers from June to August. FA: Symphyotrichum umbellatus, flat-topped aster. 3–7’H x 3–7’W. White to yellowish-centered flowers in the fall. AS: Symphyotrichum novae-angliae, New England aster. 3–7’H x 3–7’W. Purple flowers in the fall. H: Helenium autumnale, perennial sunflower, 3–5’H x 2–3’W. Lots of yellow flowers in the fall. *Woody shrubs: Though they may shed their leaves, the woody structure of these plants will provide winter interest in the garden. **Perennials: These plants die over the winter and sprout new shoots in the spring. Sometimes some of last year’s foliage will survive the winter, but generally you should trim off the dead foliage in late fall and wait for the green growth of spring.6 UNIVERSITY OF MAINE COOPERATIVE EXTENSION
  7. 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. 6–10’H x 6–10’W. Showy golden yellow fall color. Long-lasting, scented yellow flowers 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 in late spring, tolerates wet feet.IV: Ilex verticillata, winterberry. 6–8’H x 6–8’W. Plant a male and female to take advantage of showy orange berries that persist all winter long.Perennials:**RF: Osmunda regalis, royal fern. 2–5’H x 2–5’W. Large, showy fern. Needs moisture! You must keep this plant watered if you are experiencing low rainfall.C: Aquilegia canadensis, native colombine. 1–2’H x 1–2’W. Showy red and yellow flowers in spring. Sometimes blooms again in autumn. Beautiful foliage.S: Onoclea sensibilis, sensitive fern. 2H x 18”W. Soft, green fern. Thrives in moist areas.CA: Lobelia cardinalis, cardinal flower. 2–4’H x 1’W. Bright red flowers from July to September.Plants for the dryer outer edge ofthe garden:Woody shrubs:*W: Comptonia peregrina, sweetfern. 2–4’H x 2–4’W. Rickrack-shaped leaves are heavily scented when crushed. Comptonia should be purchased in sod form as it is difficult to establish individual plants. Tolerates sandy, dry, rocky soil.AR: Arctostaphylos uva-ursi, bearberry. 6–12”H x 1-2W. Shiny evergreen leaves turn bronze in the fall. Small white to pink flowers in the early spring, bright red berries in late summer that persist through winter. Tolerates sandy, dry, rocky soil. PHOTO: EDWIN REMSBERG, USDA-CSREESPerennials:**G: Geranium maculatum, wild geranium. 1–2’H x 2’W 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 year’s 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. 8. Resources Native plant lists from the Portland Water District and the Maine Developed by UMaine Extension Department of Environmental Protection: part of the Conservation Assistant Scientist Laura Wilson Practices for Homeowners fact sheet series. Available at and Water Resource Specialist Mary Gilbertson of the Portland Native 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 McCaskill Native 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. Landscapes for Maine bulletins from UMaine Cooperative Extension. A Member of the University of Maine System Available at or by calling 800-287-0274 Published 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 Land Designing Your Landscape for Maine, bulletin #2701 (Orono, ME: Grant University of the state of Maine and the U.S. Department of Agriculture cooperating. Cooperative 2005). Extension and other agencies of the U.S.D.A. Gardening to Conserve Maine’s Native Landscape: Plants to Use and provide equal opportunities in programs and employment. 11/06 Plants to Avoid, bulletin #2500 (Orono, ME: 2003). Produced by the UMaine Cooperative Native 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 Cooperative State Research, blwq/docwatershed/bufhand.htm. Education, and Extension Service, U.S. Department of Need an expert? Agriculture, under agreement nos. 2003-51130-02074 and In Central or Northern Maine: 2004-51130-03108, through the CSREES Laura Wilson, Extension Assistant Scientist New England Regional Water Quality University of Maine Cooperative Extension Program. 495 College Avenue Orono, ME 04473-1294 207-581-2971 or In Southern Maine: Mary Gilbertson, Water Resource Specialist Portland Water District 1 White Rock Road Standish, ME 04084 207-774-5961 x3336 or References Bannerman, 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): 123–128. Wilson, G. “Burnsville Rainwater Gardens.” Land and Water 48, no. 58 UNIVERSITY OF MAINE COOPERATIVE EXTENSION