Austin Texas Rain Garden Fact Sheet

1. earth-wise guide to
Rain Gardens
Keeping Water on the Land
What is a
rain garden?
A rain garden is a shallow, vegetated
depression designed to absorb and
filter runoff from hard (impervious)
surfaces like roofs, sidewalks, and
driveways. Rain gardens are usually
planted with colorful native plants
and grasses. They not only provide
an attractive addition to the yard,
but also help to conserve water and
protect our water quality.
How does a rain
garden help?
As Austin becomes increasingly
urbanized, native landscapes are
replaced with impervious surfaces
that prevent rainwater from soak-
ing into the ground. Stormwater Photo: Mary Ann Ryan - Master Gardener
quickly runs off these hard surfaces,
picking up any pollutants from the
land and carrying them to our
creeks. This rapidly flowing water Create A Rain Garden in Six Steps
also increases the chances of flood-
ing and erosion.
The goal of a rain garden is to keep Find the Right Select an area on gently sloping or
water on the land. Rain gardens, flat land
with their shallow depressions, Location
Verify the slope of your lawn
capture stormwater and provide Observe the flow of water (instructions on next page). Slope
for natural infiltration into the soil. from rooftops, driveways or should less than 10%
This provides water for the plants other hard su
surface and place the raingarden
and helps maintain a constant flow where this water collects If possible, pick a spot in full to partial
of water in our streams through sun. Shady locations will still work, but
groundwater. They also help filter the options for attractive plants are
out pollutants including fertilizers, more limited in the shade
pesticides, oil, heavy metals and Make sure that any overflow does not
other chemicals that would oth- cause unintended runoff to a neighbor’s
erwise reach our creeks through property or other structure
storm drains or drainage ditches.
By reducing the quantity of water If you are experiencing drainage-related
that runs off your property, rain gar- problems (e.g. severe foundation prob-
dens help lower the risk of flooding lems, erosion or local flooding), consider
and erosion. placing the rain garden at least 10’ away
from the structure
Avoid areas with utility lines. Be sure to
call 1-800-DIG-TESS (344-8377) to iden-
tify the location of underground utilities
www.growgreen.org – the service is free

2. How to Calculate the Slope of Your Lawn
6” 120” = .05 x 100 = 5% slope
1. Pound one stake in the ground at the 4. Measure the distance in inches between
uphill end of your rain garden site and the two stakes
pound another stake in the ground at 5. Now measure the height in inches on the
the downhill end. The stakes should be downhill stake between the ground and
about 10’ apart string
2. Tie a string to the bottom of the uphill 6. Divide the height between the ground
stake and run the string to the and string by the distance between the
downhill stake two stakes and multiply the result by 100
3. Using a string or carpenter’s level, make to find the lawn’s percent slope
the string horizontal and tie the string to
the downhill stake at that height
Test the Soil Finally, divide this area by 6. This
Calculate the Size
When soil is saturated calculation tells you how large the
(after you’ve irrigated and Shape of Your rain garden should be to hold 1”
or it has rained,) dig a Garden of runoff in a rain garden that is 6”
hole 6” in diameter and Through observation, locate the deep (see options below)
12” deep in the area you’d like to put roof area or other impervious
the rain garden. (Ideally, you want to surface that will contribute runoff Impervious Surface Raingarden Size Options
be sure there is at least the 12” of soil Area (sq. ft.) (sq. ft.) (ft. x ft.)
to your rain garden
above bedrock) 200 33 3x11or 4x9
Use a tape measure to estimate
the size of the area. This doesn’t 400 67 5x14; 7x10
require climbing on the roof! 600 100 5x20; 8x12
Standing on the ground, measure 800 133 6x22; 10x13
the footprint of the area you are 1000 167 6x28; 10x17
interested in (the area taken up
by your house if you were looking Remember more than one raingar-
down from above) den might be needed to collect all
Once you have estimated the length the run off from your roof
and width, multiply the two mea- Rain gardens shouldn’t be just func-
surements to get the area of the tional - they should be attractive,
impervious surface in square feet creative and fun!
Each Drainage Area = 1/4 of rooftop
60’
Downspout
Total Rooftop = 1800 sq. ft.
Insert a ruler and fill the hole with 30’
water up to the 6” mark. Time how 30’
long it takes the water to be ab-
sorbed into the ground 15’ 1/4 Rooftop = 450 sq. ft.
4 o t p 4 q
The water should absorb in less than
24 hours. If there is still water in the
hole after 24 hours, then the site is
not suitable for a rain garden
If your soils meet the infiltration test 75 sq. ft.
75 sq. ft.
requirements, then you are ready to
build the garden! Drainage = 30’ x 15’ : 6 = 75 sq.’

3. R
Rain Garden
C
Construction
Once you feel
confident in the
placement of the garden, lay out the
l f h
shape using string or tape to define
where to dig
Now you are ready to dig!!!
- If the yard is fairly level (flat), just Pick
dig out the garden to a depth up the City of
of 6” Austin’s Grow Green
landscaping material (like stone or fact sheets and plant guide
- If the yard is on a gentle slope, timber). This will distribute over-
you may need to dig out soil at most areas nurseries or
flow evenly across the perimeter visit www.growgreen.org
from the upslope area to con- of the rain garden
struct a small berm (mound for proper installation
of compacted soil) at the Loosen the soil in the bottom of and establishment
downslope side of the garden the rain garden to a depth of 3 tips
inches. Top dress the loosened soil
Maintain a depth of 6 inches with compost so the soil is ready
throughout the bottom of the rain for planting
garden. A string level can help you
maintain a consistent depth If water flows quickly into the rain Plant Selection
Slope the sides of the rain garden
garden, you will need to construct and Installation
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The City of
Austin Resource
Recovery Center
offers glass mulch for
free if you load it your-
self. 10108 FM 812,
Austin,TX

7. Maintenance
Water regularly until plants are
established (usually one growing
season)
Weed as needed
Avoid fertilizing - it’s usually unnec-
essary for most native plants
If your rain garden is located near
a gutter downspout or roof val-
ley, consider adding rain barrels so
that you will have an extra store of
water for irrigating the rain gar-
den plants during dry weather. The
City of Austin Water Utility offers
rebates for the purchase of qualify-
ing rain barrels. http://www.ci.austin.
tx.us/watercon/rainbarrelprogram.htm
Observe the performance of your
rain garden over time to make sure
it functions as planned. If the wa- Suggested Plants for Central Texas Raingardens
ter remains for longer than 2 days,
amend the soil by gently cultivating
the top 4” to 6“ to break-up any Base of the garden Sides of the garden
surface crust. Add sand or compost
to create a more free-draining soil Bushy Bluestem Big Bluestem
and then re-apply mulch to Cardinal Flower Big Muhly
the surface Eastern Gamagrass Black-eyed Susan
Fall Obedient Plant Brazos Penstemon
Frogfruit Clasping Coneflower
If there is Gregg’s Mistflower Cut-leaf Daisy
standing water, will Horsetail Deer Muhly
mosquitoes be a problem? Inland Sea Oats Eastern Gamagrass
Mosquitoes should not be a Marsh Obedient Plant Gulf Coast Muhly
problem because a rain garden is Maximilian Sunflower Illinois Bundleflower
designed to only hold water for a
day or two – not long enough Salt Marsh Mallow Marsh Fleabane
for mosquitoes to complete Scarlet Rose Mallow Pink Evening Primrose
their breeding cycle. Slender Rush Pitcher Sage
Soft Rush Plains Coreopsis
Swamp Milkweed Prairie Wildrye
Swamp Sunflower Scarlet Sage
Switchgrass
For more earth-wise Water Clover
gardening tips, visit Find a Grow
Water Daisy Green Landscape
Design Template to
www.growgreen.org White-topped Sedge match your needs
and style.
Wooly Rose-Mallow
For water conserving
tips and rebates, visit
www.waterwiseaustin.org
www.ci.austin.tx.us/
974-2550 854-9600 growgreen/landscape_templates.htm