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.
Kentucky Residential Rain Gardens ~ University of Kentucky
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
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
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
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.
71.
72.
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
74.
75.
76.
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.