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Residential Rain Gardens

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

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Residential Rain Gardens

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  1. Residential Rain Gardens Graphic: City of Maplewood University of Minnesota Master Gardener Program

  2. A rain garden is a water-quality tool that you can use in your own yard.

  3. What We’ll Cover • What is a “rain garden”? • Functions and benefits • How to make one • Plant selection • Maintenance • Cost • Helpful resources

  4. 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

  5. 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

  6. A rain garden is also known as ... • Mini wetland • Water quality garden • Stormwater marsh • Planted swale • Bio-retention pond • Strategically placed puddle

  7. 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

  8. 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

  9. Polluted runoff harms water quality • Flows into waterways untreated • Harms fish and wildlife • Kills vegetation • Fouls drinking water supplies • Makes recreation areas unsafe

  10. 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

  11. Design Features are Flexible Variables include: • Location • Soil • Size and shape • Plants

  12. Location of the rain garden © Fitch & Co. www.montgomerycountymd.gov/mc/services/dep/greenman/rain.htm

  13. 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

  14. Project and photo by Kestrel Design Group

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

  16. Bird’s-eye view of rain garden locations Graphic: UW Extension Service

  17. Traditional path of roof runoff Graphic: Applied Ecological Services, Inc.

  18. Average runoff from a roof is 24,000 gallons per year That would fill 600 bathtubs!

  19. Roof runoff directed to rain garden

  20. Rain Gardens in Home Landscapes In a back yard catching runoff from the garage In a front yard catching runoff from a downspout

  21. 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

  22. 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

  23. 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

  24. 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

  25. 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

  26. A soil berm acts like a bumper – keeps water from flowing over edge Berm Photo: UW Extension Publication GWQ037

  27. Rain Garden Collects Parking Lot Runoff Photos & design: Kestrel Design Group Spray paint outlines the garden shape

  28. 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

  29. Bird’s-eye view of a rain garden Graphic: UW Extension Publication GWQ037

  30. Layout for a 140-sq.ft.-garden Graphic: UW Extension Publication GWQ037

  31. Before Buried pipe connects to downspout Berm Photos: Mary Nolte After

  32. Plants for Rain Gardens

  33. 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

  34. 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

  35. Prairie plants have deep roots Graphic: Conservation Design Forum Inc.

  36. Rain gardens in Maplewood, MNinstead of curbs and gutters Photo: City of Maplewood

  37. Sun gardens Photos: City of Maplewood

  38. Garden for light shade Photo: City of Maplewood

  39. An easy shrub garden Shrubs: • Annabelle Hydrangea • American Highbush Cranberry • Anthony Waterer Spirea Perennials: • Marsh Milkweed • Stello d’Oro Daylily Photo: City of Maplewood

  40. 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

  41. 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.

  42. 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

  43. Summary • Shallow saucer shape • Strategic location • Plants match soil and moisture levels • Soil drains • Size appropriate for yard and drainage area Photo: Mary Nolte

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