Residential Rain Gardens: A Guide to Design and Plant Selection
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Residential rain gardens are low areas planted with native vegetation that intercept stormwater runoff and allow it to infiltrate the soil. They reduce runoff by 30% more than lawns by promoting more infiltration. Rain gardens increase groundwater recharge, help protect against flooding and pollution, and provide wildlife habitat. When designing a rain garden, consider the size based on the drainage area and type of soil. Native plants that tolerate wet and dry periods are recommended. Proper installation and mulching helps rain gardens become self-sustaining landscaping features.
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Residential Rain Gardens: A Guide to Design and Plant Selection
- 1. Residential Rain Gardens Rick Durham Consumer Horticulture Extension Specialist University of Kentucky
- 2. Rain garden – strategically located low area planted with native vegetation that intercepts runoff and allows it to infiltrate the soil.
- 3. Photo Copyright 1999, Center for Watershed Protection Why Should We Consider Rain Gardens?
- 4. Run Off • Typical run off from a city block is 9X greater than a wooded area of similar size due to pavement •• Grass lawn reduces run-off substantially, but not completely • Rain gardens promote 30% more infiltration than lawns
- 8. Flooding from 3” Rainfall
- 9. Rain Garden? No! Erosion and nutrient run off upstream results in siltation downstream.
- 10. Rain Gardens • Increase the amount of water that infiltrates the soil to recharges aquifers • Help protect community from flooding and drainage problems • Help protect streams and lakes from pollutants carried in run off • Enhance neighborhood beauty • Provide wildlife habitat
- 11. Rain Gardens Can Be Beautiful
- 15. Excavation of an infiltration trench
- 17. Overflow to Storm Drain
- 18. Stormwater Runoff Solutions begin by reducing the amount of impermeable surfaces.
- 21. Grass Pave
- 22. Single Family Residence or Commercial Property
- 23. Ok, Let’s Now Take a Look at Rain Gardens
- 24. Getting Started • How Big does it need to be? • Where do I need to locate it? • Soil Considerations? •• What Plants should we use?
- 25. How big do I make my rain garden ? •Design it to handle a 1.25 inch rain event (this captures 80% of rainfall events) ••Square footage x 1.25 in. (or .104 ft) = X cu ft of water
- 26. 60 feet 30 feet 60 x 30 = 1800 sq. ft. 1800 sq. ft. x .104 ft. of rain (1.25 in rain)= 187 cu. Ft. of water Just for Fun 187 cu. ft. of water x 7.48 = 1398 gallons
- 27. 187 cu. Ft. of water 10 x 12 x 1.5 feet deep = 180 cu. Ft.
- 28. Size of Rain Garden • Rain Gardens can be of any size or shape • Sandy soil, garden should be 20-30% of the size of the drain area • Heavy clay soils, garden should be 50- 60% the size of the drain area • Most residential rain gardens will be 100-300 sq. ft.
- 29. Where does it need to be? • Locate the rain garden down slope from any buildings • Away from large trees (easier digging) •• In areas that take advantage of natural slope. • Consider the size and placement in the landscape design. It may be easier to create two separate rain gardens.
- 30. Excavating • For large projects it may be easier to hire a landscaper. • For smaller projects use the excavated soil to build a berm on the downhill side of the garden. • Use a rope or water hose to layout the edge of the garden, use stakes and string to level. • For deep gardens set aside the top 4-6 inches of soil (topsoil), excavate the hole then use the top soil to backfill the planting area.
- 31. Soil Considerations • Do a perk test. Dig a hole 8 inches deep and fill with water. If it takes more than 24 hours to drain then the soil needs to be amended. • On poorly drained soil excavate 10-12 inches of soil from hole, mix 3-6 inches of coarse sand or small gravel with excavated soil and replace into rain garden. • Bring 2 cups of soil to Extension Office for soil test Add lime and fertilizer according to soil test results, 3-6 inches of organic matter then till to a depth of 6 inches. • Rain garden soil mix = 50-60% sand, 20-30% top soil, 20-30% compost (Rain Gardens of Western Michigan)
- 32. What about mosquitoes? • Life cycle requires 7-14 days from egg to adult • Require standing water during juvenile stages • Most rain gardens will drain within 3-4 days, usually sooner A properly designed rain garden will not breed mosquitoes!
- 33. Now the fun part… Picking the plants • Determine sun exposure – Full sun = 6 or more hours of direct sun – Part Sun to Part Shade= • less than 6 hours of direct sun – Shade = virtually no direct sun - problems • Don’t forget specific site problems – Plants will need to be watered until established – Weed management strategy needed for first year or so – Choose native were possible. Drought tolerant, deep rooted, deer resistant?
- 34. Trees • Deciduous / Evergreen • Plant as Specimens or in Groups • Consider Bark / Shape / Flowering • Provide Habitats for Birds
- 35. Trees for Rain Gardens • Sweetbay Magnolia • Winter King Hawthorn • Hackberry • Red Maple • River Birch • Black Gum • Bald Cypress • Fringetree • Ginko • Willow Oak • Sycamore
- 36. River Birch • Distinguished by bark • 50' X 50' mature size •• Drought tolerance • Multi-stemmed
- 37. Baldcypress • Drought Tolerance • Deciduous •• Knees? • 60' x 25' • Plant as Specimen or in Groups
- 38. Red Maple • 40'-60' x 40'-60' • Drought Tolerance • Excellent Fall Color
- 39. Ginkgo • 25'-50' X 20'-40' • Pest Free / Resistance to Damage • Tolerates Most Soil Conditions
- 40. Ginkgo - Fruit / Leaf • Fan Shaped Leaf • Undesirable Fruit
- 41. Black Gum • Nyssa sylvatica • 60-80 feet • Deciduous
- 42. Willow Oak • Quercus phellos • 40-60 ft. • ‘Hightower’
- 43. Sweetbay Magnolia • Magnolia virginiana • 20-30 ft. • Evergreen •• fragrant
- 44. Winter King Hawthorn • Crategus virdis 'Winter King‘ • Slow growth •• 15-20 ft. • Deciduous • Fall/winter berries
- 45. Hackberry • Celtis occidentalis • 80 ft. • Deciduous •• Long lived- 150 yrs.
- 46. Fringetree • Chionanthus virginicus • Small understory tree • deciduous
- 47. Shrubs for Rain Gardens • Arrowwood • Buttonbush • Summersweet Clethra • American Beautyberry • Bottlebrush Buckeye • Wax Myrtle • Inkberry • Oakleaf Hydrangea • Sweetspire
- 48. Inkberry • Drought Tolerance •• 5' x 5' • Withstands Heavy Pruning • Adapted to Various Soil Types
- 49. Arrow wood • Viburnum dentatum • 8 ft tall x 6 ft. •• Fruit eaten by birds • Fall color red to reddish purple
- 50. Bottlebrush Buckeye • Aesculus parviflora • 8-15 ft. • Deciduous •• 8-12 inch flower stalk in June
- 51. Oakleaf Hydrangea • Hydrangea quercifolia • 6 feet •• Deciduous • Great fall color
- 52. Sweetspire • Itea • 4-5 feet tall and wide • Great burgundy fall color • May-June white fragrant flowers resembling fluffy caterpillars
- 53. Buttonbush • Cephalanthus occidentalis • 18 ft. •• Bees and butterflies • Fragrant • Dried flowers often remain through winter
- 54. Sweet Pepperbush (Summer Sweet Clethra) • Clethra alnifolia • Blooms June- July • Drought Tolerant • Yellow Fall Color • Excellent Fragrance • 10 ft.
- 55. American Beautyberry • 6' x 6' • Drought Tolerance • Cut Back Each Year • Berries for Wildlife
- 56. Herbaceous Plants for Rain Gardens • Swamp Milkweed • Cinnamon Fern • Canna Lilies • Yellow Flag Iris • Asters • Blackeyed Susan • Lobelia • Goldenrod • Rushes • Liriope/Mondograss • Ironweed • Joe Pye Weed • St. Johns Wort
- 57. Asters Aster novae-angliae New England Aster Color:purple Height: 27““ Late summer/fall flowering
- 58. Blackeyed Susan • Rudbeckia • 'Indian Summer‘ • ‘Goldstrum’ •• Mid to late summer flowering • Foliage 8-12 inches • Flowers up to 2 feet
- 59. Cardinal Flower • Lobelia cardinalis – Cardinal Flower • Red flowers in later summer and fall • 2-4 feet tall • Few pests
- 60. Goldenrod • Solidago Goldenrod • Height: cultivar dependent, 3-6 feet • Late summer/fall flowering • Not considered a contributor to hay fever
- 61. St. Johns Wort • Hypericum spp. • 200 species • Ground cover to medium shrub
- 62. Swamp Milkweed • Asclepias incarnata • Summer flowers • Butterflies •• Might see some aphids
- 63. Ironweed • Vernonia noveboracensis • Flowers mid to late summer • Height to 6 feet • Butterflies
- 64. Liriope • Great Border • Ground Cover • Grows in Moist Areas • Easy to Grow • Increase by Division
- 65. Cinnamon Fern • Osmunda cinnamomea • Deciduous •• 2-5 feet ht.
- 66. Joe Pye Weed • Eupatorium • Late Summer Flowers • Tall Robust Plant • Flower heads attractive after plant dries in fall
- 67. Miscanthus sinensis Silver Grass Grasses Pennisetum alopecuroides Fountain Grass Phalaris arundinaceae Ribbon Grass Festuca cinerea Silver Fescue
- 68. Rushes and Sedges • Juncus and Carex • Grass-like • Tolerant of wet sites •• Drought tolerant as well
- 69. Planting Trees and Shrubs When planting individual plants, dig the hole 2-times wider than the root ball. When planting a group of plants, cultivate the planting area to a 12-inch depth. Do not add amendments to individual planting holes. Instead, incorporate amendments uniformly into the top 12 inches of the soil. Remove the wire or cord from around the stem of B&B plants.
- 70. Planting Trees and Shrubs Slice or break apart the root ball of pot-bound container-grown plants. Install guy wires on trees, if necessary, but remove them after establishment. A water saucer may be used to help direct water to the roots, but it is only temporary. Mulch. Water to settle soil.
- 73. If a water saucer is used, rake it outward and away from the planting hole. Smooth saucer 2 to 3 months after planting to keep it from eroding over the roots
- 77. Planting herbaceous plants • Plant in waves rather than as single plants • Consider height and period/color of bloom • Plant no deeper than previously growing •• Water thoroughly at planting • Provide 1” water per week until established • Prune back vegetation prior to regrowth in spring
- 78. Mulch – A minimum of 2” needed, not more than 4” – Keeps weeds down – Acts as sponge to capture heavy metals, oils and grease – Holds moisture – Maintains even temperature – Shredded hardwood mulch or pine straw recommended
- 79. Pondering Points • The planting plan design should include species that tolerate extremes. •• Rain gardens can be left to evolve into a natural wild condition. • Native plants are best adapted to local climate and once established are generally low maintenance.
- 80. Pondering Points (continued) • When planted with native species rain gardens can have additional value as a wildlife habitant. • Shrub, trees, and ground covers absorb up to 14 times more rainwater than a grass lawn.
- 81. Maintenance? • No special maintenance required once established •• Routine periodic landscaping maintenance – Weeding – Irrigation – Pruning/vegetation removal
- 82. For more information: • Rain Gardens of Western Michigan http://www.raingardens.org/Index.php • Rain Gardens – Gardening with water quality in mind. http://www.mninter.net/~stack/rain/ •• Rain gardens infiltrating Wisconsin http://www.dnr.state.wi.us/org/water/wm/nps/rg/ Credits: • Residential Rain Gardens. Todd Hurt, UGA/ Cherokee Co. Extension. Milti-state Master Gardener Educator Training: Landscape Water Quality Workshop, Griffin, GA. 2004.