1 © 2011 Regents of the University of Minnesota. All rights reserved. 11 RESIDENTIAL RAIN GARDENS Graphic: City of Maplewood

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© 2011 Regents of the University of Minnesota. All rights reserved.

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RESIDENTIAL RAIN GARDENS

Gra

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: C

ity

of M

aple

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d

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A rain garden is a

water-quality tool

that you can use

in your own yard.

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WHAT WE’LL COVER What is a “rain garden”? Functions and benefits How to make one Plant selection Maintenance Cost Helpful resources

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WHAT IS A “RAIN GARDEN”? A shallow sunken garden that recycles the rain

– less than 8” deep Rainwater runoff is directed toward it Runoff soaks in

Photo: Mary Nolte, Fulton neighborhood, Minneapolis

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PLANTS HELP RECYCLE THE RAIN Plant roots

absorb water Water goes up

the stem Leaf surfaces release

moisture Water returns to

the atmosphere as a vapor

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A RAIN GARDEN IS ALSO KNOWN AS ... Mini wetland Water quality garden Stormwater marsh Planted swale Bio-retention pond Strategically placed puddle

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FUNCTIONS OF A RAIN GARDEN Diverts runoff from paved surfaces

– Driveways, roofs, streets, patios, walks Water moves “sideways” – runs off pavement

Keeps runoff on site– Instead of flowing untreated into streams and

storm sewers

Soil acts like a living sponge– Water moves “down” - into the ground

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BENEFITS OF A RAIN GARDEN Soaks up 30% more runoff than lawns Filters polluted runoff

• sediments, fertilizers, pesticides

Recharges groundwater Helps prevent flooding Provides habitat/food for butterflies, birds Beautifies a low spot in the yard

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POLLUTED RUNOFF HARMS WATER QUALITY

Flows into waterways untreated

Harms fish and wildlife

Kills vegetation Fouls drinking

water supplies Makes recreation

areas unsafe

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EVERY CURB IS A SHORELINE

Grass clippings and leaves are the main source of phosphorus in lakes and streams

Rain gardens act as filters and remove:– 94% of sediment– 43% of phosphorus– 70% of nitrogen

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DESIGN FEATURES ARE FLEXIBLEVariables include: Location Soil Size and shape Plants

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www.montgomerycountymd.gov/mc/services/dep/greenman/rain.htm

© Fitc

h &

Co

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LOCATION OF THE RAIN GARDEN

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GO WITH THE FLOW Observe the drainage pattern in your yard Locate the garden:

– in a natural low spot– near sidewalks, driveways, or other paved surfaces– down-slope from roofs, gutters, downspouts, sump

pump outlet

Direct water into rain garden– channel or buried plastic pipe

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Project and photo by Kestrel Design Group

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Locate the rain garden at least 10 feet from the house, on a gentle slope

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BIRD’S-EYE VIEW OF RAIN GARDEN LOCATIONS

Gra

ph

ic:

UW

Ext

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n S

erv

ice

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TRADITIONAL PATH OF ROOF RUNOFF

Graphic: Applied Ecological Services, Inc.

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Average runoff from a roof is 24,000 gallons per year

That would fill 600 bathtubs!

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ROOF RUNOFF DIRECTED TO RAIN GARDEN

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RAIN GARDENS IN HOME LANDSCAPES

In a back yard catching runoff from the garage

In a front yard catching runoff from a downspout

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THE SOIL MUST DRAIN! A rain garden is NOT a pond. Percolation test:

– fill a 6-inch-deep hole with water– should drain within 24 hours– if not, don’t put a rain garden there– or amend soil

“Rain garden soil mix”– 50-60% sand, 20-30% topsoil, 20-30a% compost

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HOW BIG? No standard size Rule of thumb: 1/3 of drainage area

– e.g., 170 sq. ft. (10’ x 17’) garden for 500 sq. ft. of drainage area

Factors include slope, soil type, distance from runoff point

Even a small rain garden is beneficial

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CALCULATING DRAINAGE AREA Area of roof

going to down spout

Length of house 100 feet Width of house 20 feet L X W = 2000 sq ft 2000 sq ft ÷ 4 =

500 sq ft draining to the rain garden

Width

Length

Graphic: UW Extension Service

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DESIGNING THE RAIN GARDEN Call Gopher State One: 800-252-1166 Outline it with rope or hose

curvy shape

Remove sod and dig to desired depth

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DESIGNING THE RAIN GARDEN Features:

gently sloping sides flat in the deepest spot berm at low end grass filter strip on top edge mulch – shredded bark

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A soil berm acts like a bumper – keeps water from flowing over edge

Photo: UW Extension Publication GWQ037Berm

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RAIN GARDEN COLLECTS PARKING LOT RUNOFF

Photos & design:

Kestrel Design Group

Spray paint outlines the garden shape

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Parking lot runoff

flows into the rain garden instead of into the street

Runoff pools in the garden, then seeps into the ground

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Graphic: UW Extension Publication GWQ037

BIRD’S-EYE VIEW OF A RAIN GARDEN

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LAYOUT FOR A 140-SQ.FT. GARDEN

Graphic: UW Extension Publication GWQ037

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Photos: Mary Nolte

Before

After

Buried pipe connects to downspout

Berm

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PLANTS FOR RAIN GARDENS

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SELECT PERENNIAL PLANTS THAT Tolerate both wet and dry spells

– plants that like wet feet in deepest part e.g.: Blue flag iris, marsh milkweed, big bluestem,

sedges, red-twigged dogwood, buttonbush

Tolerate de-icing salts (if near roads) Match up with soil and light conditions

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NATIVE PLANTS HAVE ADVANTAGES

Adapted to the climate and native pests

Deep rooted– long roots make

channels in the soil for water to follow

Havens for butterflies, birds, beneficials

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PRAIRIE PLANTS HAVE DEEP ROOTS

Graphic: Conservation Design Forum Inc.

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RAIN GARDENS IN MAPLEWOOD, MN INSTEAD OF CURBS AND GUTTERS

Photo: City of Maplewood

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SUN GARDENS

Photos: City of Maplewood

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GARDEN FOR LIGHT SHADE


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Shrubs: Annabelle Hydrangea American Highbush

Cranberry Anthony Waterer SpireaPerennials: Marsh Milkweed Stello d’Oro Daylily

AN EASY SHRUB GARDEN


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MAINTENANCE Pull weeds (esp. the 1st year) Water ~3 x a week until established

– also during a dry spells

Mulch – shredded hardwood won’t float away

Cut back or mow down

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WHAT ABOUT MOSQUITOES? A rain garden is not a pond No standing water between rainfalls Mosquitoes need at least 7 days in

standing water to hatch– will not survive if wetland dries out in less than

a week

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ESTIMATED COST AND PLANTS NEEDED Do-it-yourselfers:

– about $3 to $5/sq. ft.

Professionals: – about $10 - $12/sq.ft

Plants needed for 300 sq. ft. garden– 100 for wet zones – 200 for upland zones

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Shallow saucer shape Strategic location Plants match soil and

moisture levels Soil drains Size appropriate for

yard and drainage area

SUMMARY

Photo: Mary Nolte

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1 © 2011 Regents of the University of Minnesota. All rights reserved. 11 RESIDENTIAL RAIN GARDENS Graphic: City of Maplewood