Residential Rain Gardens Graphic: City of Maplewood University of Minnesota Master Gardener Program
A rain garden is a water-quality tool that you can use in your own yard.
What We’ll Cover • What is a “rain garden”? • Functions and benefits • How to make one • Plant selection • Maintenance • Cost • Helpful resources
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
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
A rain garden is also known as ... • Mini wetland • Water quality garden • Stormwater marsh • Planted swale • Bio-retention pond • Strategically placed puddle
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
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
Polluted runoff harms water quality • Flows into waterways untreated • Harms fish and wildlife • Kills vegetation • Fouls drinking water supplies • Makes recreation areas unsafe
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
Design Features are Flexible Variables include: • Location • Soil • Size and shape • Plants
Location of the rain garden © Fitch & Co. www.montgomerycountymd.gov/mc/services/dep/greenman/rain.htm
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
Bird’s-eye view of rain garden locations Graphic: UW Extension Service
Traditional path of roof runoff Graphic: Applied Ecological Services, Inc.
Average runoff from a roof is 24,000 gallons per year That would fill 600 bathtubs!
Rain Gardens in Home Landscapes In a back yard catching runoff from the garage In a front yard catching runoff from a downspout
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
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
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 Area of roof going to down spout Calculating Drainage Area Length Width Graphic: UW Extension Service
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
Designing the rain garden – cont’d Features: • gently sloping sides • flat in the deepest spot • berm at low end • grass filter strip on top edge • mulch – shredded bark
A soil berm acts like a bumper – keeps water from flowing over edge Berm Photo: UW Extension Publication GWQ037
Rain Garden Collects Parking Lot Runoff Photos & design: Kestrel Design Group Spray paint outlines the garden shape
Parking lot runoff flows into the rain garden instead of into the street Runoff pools in the garden, then seeps into the ground Photo nd Project by Kestrel Design Group
Bird’s-eye view of a rain garden Graphic: UW Extension Publication GWQ037
Layout for a 140-sq.ft.-garden Graphic: UW Extension Publication GWQ037
Before Buried pipe connects to downspout Berm Photos: Mary Nolte After
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
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
Prairie plants have deep roots Graphic: Conservation Design Forum Inc.
Rain gardens in Maplewood, MNinstead of curbs and gutters Photo: City of Maplewood
Sun gardens Photos: City of Maplewood
Garden for light shade Photo: City of Maplewood
An easy shrub garden Shrubs: • Annabelle Hydrangea • American Highbush Cranberry • Anthony Waterer Spirea Perennials: • Marsh Milkweed • Stello d’Oro Daylily Photo: City of Maplewood
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
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.
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
Summary • Shallow saucer shape • Strategic location • Plants match soil and moisture levels • Soil drains • Size appropriate for yard and drainage area Photo: Mary Nolte