Graphic: City of Maplewood
RESIDENTIAL RAIN GARDENS
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© 2011 Regents of the University of Minnesota. All rights reserved.
A rain garden is a
water-quality tool
that you can use
in your own yard.
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WHAT WE’LL COVER
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What is a “rain garden”?
Functions and benefits
How to make one
Plant selection
Maintenance
Cost
Helpful resources
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© 2011 Regents of the University of Minnesota. All rights reserved.
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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© 2011 Regents of the University of Minnesota. All rights reserved.
A RAIN GARDEN IS ALSO KNOWN AS ...
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Mini wetland
Water quality garden
Stormwater marsh
Planted swale
Bio-retention pond
Strategically placed puddle
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© 2011 Regents of the University of Minnesota. All rights reserved.
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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© 2011 Regents of the University of Minnesota. All rights reserved.
BENEFITS OF A RAIN GARDEN
 Soaks up 30% more runoff than lawns
 Filters polluted runoff
• sediments, fertilizers, pesticides
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Recharges groundwater
Helps prevent flooding
Provides habitat/food for butterflies, birds
Beautifies a low spot in the yard
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© 2011 Regents of the University of Minnesota. All rights reserved.
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 FLEXIBLE
Variables include:
 Location
 Soil
 Size and shape
 Plants
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© 2011 Regents of the University of Minnesota. All rights reserved.
© Fitch & Co.
LOCATION OF THE RAIN GARDEN
www.montgomerycountymd.gov/mc/services/dep/greenman/rain.htm
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© 2011 Regents of the University of Minnesota. All rights reserved.
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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© 2011 Regents of the University of Minnesota. All rights reserved.
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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Graphic: UW Extension Service
BIRD’S-EYE VIEW OF RAIN
GARDEN LOCATIONS
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© 2011 Regents of the University of Minnesota. All rights reserved.
TRADITIONAL PATH OF ROOF RUNOFF
Graphic: Applied Ecological Services, Inc.
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© 2011 Regents of the University of Minnesota. All rights reserved.
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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© 2011 Regents of the University of Minnesota. All rights reserved.
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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© 2011 Regents of the University of Minnesota. All rights reserved.
THE SOIL MUST DRAIN!
 A rain garden is NOT a pond.
 Percolation test:
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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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© 2011 Regents of the University of Minnesota. All rights reserved.
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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© 2011 Regents of the University of Minnesota. All rights reserved.
CALCULATING DRAINAGE AREA
Area of roof going
to down spout
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L
e
n
g
t
h
Width
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
Graphic: UW Extension Service
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© 2011 Regents of the University of Minnesota. All rights reserved.
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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© 2011 Regents of the University of Minnesota. All rights reserved.
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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© 2011 Regents of the University of Minnesota. All rights reserved.
A soil berm acts like a bumper –
keeps water from flowing over edge
Photo: UW Extension Publication GWQ037
Berm
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© 2011 Regents of the University of Minnesota. All rights reserved.
RAIN GARDEN COLLECTS PARKING LOT RUNOFF
Photos & design:
Kestrel Design Group
Spray paint outlines
the garden shape
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Photo and Project by Kestrel Design Group
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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BIRD’S-EYE VIEW OF A RAIN GARDEN
Graphic: UW Extension Publication GWQ037
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LAYOUT FOR A 140-SQ.FT. GARDEN
Graphic: UW Extension Publication GWQ037
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© 2011 Regents of the University of Minnesota. All rights reserved.
Before
Buried pipe connects to downspout
Berm
Photos: Mary Nolte
After
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PLANTS FOR RAIN GARDENS
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© 2011 Regents of the University of Minnesota. All rights reserved.
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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© 2011 Regents of the University of Minnesota. All rights reserved.
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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© 2011 Regents of the University of Minnesota. All rights reserved.
RAIN GARDENS IN MAPLEWOOD, MN
INSTEAD OF CURBS AND GUTTERS
Photo: City of Maplewood
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© 2011 Regents of the University of Minnesota. All rights reserved.
SUN GARDENS
Photos: City of Maplewood
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© 2011 Regents of the University of Minnesota. All rights reserved.
GARDEN FOR LIGHT SHADE
Photo: City of Maplewood
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© 2011 Regents of the University of Minnesota. All rights reserved.
AN EASY SHRUB GARDEN
Shrubs:
 Annabelle Hydrangea
 American Highbush
Cranberry
 Anthony Waterer Spirea
Perennials:
 Marsh Milkweed
 Stello d’Oro Daylily
Photo: City of Maplewood
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© 2011 Regents of the University of Minnesota. All rights reserved.
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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© 2011 Regents of the University of Minnesota. All rights reserved.
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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© 2011 Regents of the University of Minnesota. All rights reserved.
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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© 2011 Regents of the University of Minnesota. All rights reserved.
SUMMARY
Photo: Mary Nolte
 Shallow saucer shape
 Strategic location
 Plants match soil and
moisture levels
 Soil drains
 Size appropriate for
yard and drainage
area
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© 2011 Regents of the University of Minnesota. All rights reserved.
Discover more at
extension.umn.edu
© 2011 Regents of the University of Minnesota. All rights reserved.
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