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8/7/2019 How to Build a Rain Garden
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A STEP-BY-STEP GUIDE TO
LandscapingFORClean WaterANDHealthy Streams
THE OREGON
Ran Grden Guid
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams2
The Oregon Rain Garden Guide:Landscaping or Clean Water and Healthy Streams
Text by Robert Emanuel and Derek Godwin, Oregon Sea Grant Extension, Oregon State University (OSU);and Candace Stoughton, East Multnomah Soil and Water Conservation District.
Sample rain garden layouts by Heidi Brill. Plant list compiled and edited by Teresa Huntsinger, Oregon Environmenta
Council. Other signicant contributors include Angela Boudro, Jackson Soil and Water Conservation District; Linda
McMahan, OSU Extension Service, Yamhill County; Joy Jones, OSU Extension Service, Tillamook County; and Neil
Bell, OSU Extension Service, Marion County. Editing by Rick Cooper, graphic design by Patricia Andersson, Oregon Sea
Grant, OSU.
Cover artwork: Rain Garden painted by John C. Pitcher Good Nature Publishing 2009.
www.goodnaturepublishing.com 800-631-3086
This project has been unded in part by the United States Environmental Protection Agency under assistance agree-
ment CP-0045105 to the Oregon Department o Environmental Quality. The contents o this document do notnecessarily refect the views and policies o the Environmental Protection Agency, nor does mention o trade names
or commercial products constitute endorsement or recommendation or use.
Many thanks to those who reviewed this document, plant lists, and sample planting designs or accuracy and appro-
priateness. Special thanks to those who made contributions o photos or text.
2010 by Oregon State University. This publication may be photocopied or reprinted in its entirety or noncom-
mercial purposes. To order additional copies o this publication, call 541-737-4849. This publication is available in an
accessible ormat on our Web site at http://seagrant.oregonstate.edu/sgpubs/onlinepubs.html
For a complete list o Oregon Sea Grant publications, visit http://seagrant.oregonstate.edu/sgpubs
This report was prepared by Oregon Sea Grant under award number NA06OAR4170010 (project number E/BET-02-
PD) rom the National Oceanic and Atmospheric Administrations National Sea Grant College Program, U.S. Depart-
ment o Commerce, and by appropriations made by the Oregon State legislature. The statements, ndings, conclu-
sions, and recommendations are those o the authors and do not necessarily refect the views o these unders.
Oregon Sea Grant, Corvallis, Oregon ORESU-H-10-001
The production o this guide was part o Stormwater Solutions,a collective public education eort involving several partners.
Partners responsible or the production o this guide include
the ollowing:
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams
Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
The purpose o this guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
What is a rain garden? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Why build a rain garden? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Building a Rain Garden: A Step-by-Step Approach . . . . . . . . . . . . . . . . . . . . 6
STEP 1:Observe and map your site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Determine how much area the rain garden will treat. . . . . . . . . . . . . . . . . 6
STEP 2:Determine the location o the rain garden . . . . . . . . . . . . . . . . . . . 6Go with the fow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Respect the fow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Divert the fow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Regulations, permits, and design modications . . . . . . . . . . . . . . . . . . . . 8
Measure the slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
STEP3:Assess soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Testing inltration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Determining soil texture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Interpreting the inltration test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
STEP 4:Determine the size o the rain garden . . . . . . . . . . . . . . . . . . . . . . . 11Rain garden depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Dig saely! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Delineate the rain garden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Getting water to the rain garden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
D isco nnec t ing do w nspo uts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5
Designing or overfow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Keys to success . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
STEP 5: Constructing a rain garden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17Excavating, grading, and berms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
Grading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
Plumbing the rain garden. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
To amend or not to amend? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
STEP 6:Choose the right plant or the right place . . . . . . . . . . . . . . . . . 20Planting zones and plant selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Compost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Key plant characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Planting tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
A note about invasive species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Mulching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23Watering a rain garden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
STEP 7:Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Weeding, pruning, and mulching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Dont drown your plants! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
A note about Oregons regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Sample Rain Garden Layouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Rain Garden Plant List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
For more inormation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams4
Introduction
Figure 1: Cross-section o atypical rain garden.
(Graphic by East Multnomah Soil
and Water Conservation District
[EMSWCD])
The purpose o this guide
The Oregon Rain Garden Guide was written to helpOregonians learn how to design and build rain gar-
dens to treat the stormwater runo rom their ownhomes or businesses. Rain gardens are gardens
with a purpose; they help reduce the amount o ex-
cess water and associated pollutants reaching local
lakes, streams, and bays. Ultimately this results in
healthier waterways, sh, other wildlie, and people.
This how-to guide provides inormation specic
to Oregons conditions, including the rainall and
appropriate plants or your site. You dont have to
be a stormwater, garden, or landscape proessional
to use this guide. It provides the necessary inor-
mation to saely build and maintain a rain garden,
along with reerences or more detailed guidance
or special conditions. You may also contact the
authors and partners directly or more inormation.
What is a rain garden?
A rain garden is a sunken, generally fat-bottomed
garden bed that collects and treats stormwater
runo rom rootops, driveways, sidewalks, parkinglots, and streets. Rain gardens help mimic natural
orest, meadow, or prairie conditions by inltrat-
ing stormwater rom hard suraces. A variety o
planting plans are included in this manual or your
reerence.
Rain gardens keep our watersheds healthy by
reducing fooding by absorbing rain water rom
hard suraces
ltering oil, grease, and toxic materials beore
they can pollute streams, lakes, and bays
recharging groundwater aquiers by allowing
water to soak into the ground
providing benecial wildlie habitat
RAIN GARDEN DICTIONARY:
Impervious suraces are areas that do not allow rain or snowmelt to inltrate or soak into the soilbelow the surace (or example, roos, driveways, roads, sidewalks, and patios). Some ground areas
that have been severely compacted rom heavy equipment or oot trac may also be considered
impervious i most o the water runs o the surace when it rains.
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams
Why build a rain garden?
When the Pacic Northwest was covered with
orests and prairies, rainall slowly dripped through
branches and vegetation, seeped through du,and sank into the ground as it slowly percolated to
nearby water bodies. As parts o our landscapes
became more developed, the rainall that lands on
hard suraces was routed into pipes, ditches, and
storm drains. Much o that runo is routed directly
to streams or into the sewer system. The result?
Too much water fowing in a short amount o
time, carrying pollutants that negatively aect the
health o our streams, lakes, and estuaries. Today,
managing stormwater runo by inltrating it into
the ground is one o the simplest ways to actively
protect our streams. Rain gardens help us restore
the natural water cycle in the landscape, which is
critical to ensure healthy streams in both small
towns and large cities.
Do rain gardens attract or breedmosquitoes?
No. For reproduction, mosquito larvae require
a number o days in standing water. Most
urban mosquitoes breed in places like junk
piles where there are old tires or tin cans. In awell-designed rain garden, water is rarely stand-
ing long enough or mosquito reproduction.
Ideally, a rain garden should drain so that water
wont be standing in it or more than 48 hours.
For more inormation, see Mosquitoes at
entomology.oregonstate.edu/urbanent/.
Figure 2 (top): A newly installed rain garden in
Tillamook County, Oregon.Figure 3 (middle): An established rain garden inPortland, Oregon (by Blossom Earthworks).
Figure 4 (bottom): Streams in the Pacic Northwestare normally buered rom pollution and sudden
fashes o water by their surrounding orests and
grasslands. In an urban environment, water rom
roos and streets is oten piped directly into streams,
delivering pulses o polluted, damaging water and
sometimes causing localized fooding.
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams8
HORIZONTAL DISTANCE(233)
LINE LEVEL
STAKE
RISE(18) STAKE
Regulations, permits, and designmodications
Some cities and counties have specic regulations
regarding disconnecting downspouts, routing or
piping water o-site, and setbacks to structures,
steep slopes, and property lines. They may also
require a permit. Always check with your citys
building or planning department i you live within
city limits; otherwise, check with your county
government.
Rain gardens may be designed with impermeable
liners, rock trenches, and piping to saely route
water away rom structures and o-site. These de-
signs would allow you to build rain gardens closerto structures, on steep slopes, in soils that dont
drain well, and in other challenging situations.
However, these designs are beyond the scope
o this guide. We recommend that you contact a
licensed landscape proessional or engineer or
assistance with these alternative designs.
Measure the slope
Tools needed:
Two stakes
Survey line or string
Line level
Measuring tape
Calculator
Steps:Measure and calculate the slope o the site to as-
sess how water will be routed to and rom your rain
garden. It is critical to make sure your property has
a slope o less than 10 percent beore constructing
a rain garden there.1. Place stakes in the ground at the top and bottom
o the slope to be calculated.
2. Attach a survey line (or any heavy-duty string) to
the two stakes. Be sure that the line touches the
ground on the uphill stake. Use the level to make
sure the line is level.
3. Measure the horizontal distance (along the line)
between the two stakes.
4. Measure the rise (vertical distance) rom the
ground up to the line on the downhill stake.
5. Calculate the slope by plugging your numbers
into the ollowing ormula:
Note: both measurements must use the sameincrements (or example, inches).
slope =RISE
HORIZONTAL DISTANCEx 100%
18"
Example:RISE = 18"
HORIZONTAL DISTANCE = 233"
x 100%233"
7.7 % =
Graphic:EMSWCD
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams
STEP 3: Assess soil
The ability o soil to drain water is one o the most
important considerations or understanding the
site and properly sizing a rain garden. An inltration
and texture test will help you determine the soils
capacity to absorb and percolate water down into
the lower layers.
Testing inltration
1. Dig a test hole in the area where the rain garden
will be built. Try to site the hole in the middle o
the planned rain garden. Dig a hole to the expect-
ed depth o the rain garden (rom grade to the top
o the rain gardens base). Note that ideally, this
test should be done when soils are not rozen andwhen groundwater levels may be highest, such as
in the spring.
2. Fill the hole with water to just below the rim. This
should be the same depth o water expected i the
rain garden lled to the rim. Record the exact time
you stop lling the hole and the time it takes to
drain completely.
3. Rell the hole again and repeat step 2 two more
times. The third test will give you the best mea-
sure o how quickly your soil absorbs water when
it is ully saturated, as it would be during a rainyperiod o the year or during a series o storms
that deliver a lot o rainall in a short period o
time. Building a rain garden to handle these
conditions is a way to be sure you will not cause
damage to your own or a neighbors property.
4. Divide the distance that the water dropped by the
amount o time it took or it to drop. For example,
i the water dropped 6 inches in 12 hours, then 6
divided by 12 equals 1/2 inch per hour o inltra-
tion. I the slowest inltration rate measured o
the three trials is less than 1/2 inch per hour, then
you should dig another 3 to 6 inches deeper and
repeat the above steps. Repeat this process at
various depths down to 2 eet, or until you have at
least 1/2 inch per hour inltration.
!Note: Soils with drainage o less than 1/2 inch perhour are not appropriate or rain gardens with-
out signicant modications in design. Consult
a licensed landscape proessional or engineer or
assistance in these circumstances.
1
2
3
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams10
Determining soil texture
1. Take a handul o the soil you have excavated
rom your inltration test. Pulverize it in yourhand and remove any bits o organic matter or
obvious rocks.
2. Wet it with a small amount o water and rub it
between your thumb and index nger. Dont
saturate it until it is runny mud. You might eel
stickiness, grittiness, or smoothness. The grittier
the eel, the more sand is present in your soil.
The slicker the soil, the more clay in it. Smooth
soils are sometimes an indicator o a ne silt or
loam. Discard the soil.
3. Next, take another sample in your hand. Wet it
until it has the consistency o dough. You should
be able to orm a ball that holds together with
the soil in your palm. I you cannot get the ball to
orm, then your soil is very sandy. In most soils,
however, you should be able to create a rough
ball.
4. Knead the soil together between your thumb and
ngers and attempt to orm a ribbon. As you
build the ribbon, it will either hold together or
break o. I the soil breaks quickly in the process,
then it likely has a high sand content. I the rib-
bon orms quickly and stays strong, it has moreclay.
I the soil orms a ribbon less than 1 inch in
length beore it breaks, the soil is sandy or silty.
I the soil makes a ribbon 1 to 2 inches in length
beore it breaks, the soil is clayey.
I the soil makes a ribbon greater than 2 inches
beore it breaks, it may not be suitable or a rain
garden constructed without proessional help,
depending on how ast the soil drains during the
inltration test.
Figure 7a: Conducting a soil eel test by making a ball with the moistened soil, tosee how easily it alls apart as well as what texture it has (sticky, silky, or gritty).(Photo: Gina Emanuel)
Figure 7b: Using a soil ribbon to test soil or clay, loam, or sand content. Thelonger and rmer the ribbon, the more clay content in the soil. (Photo: Gina Emanuel)
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams 1
Interpreting the inltration test
Building a better soil
Amending with compost is recommended to
improve initial plant and microbial health. I
your soil has high clay content, soil amend-
ments may be needed to improve conditions
or good plant health. Sites with very high clay
content and low drainage are usually inappro-
priate or the types o rain gardens described
in this guide, without signicantly altering the
design or better drainage (such as adding
subsurace drain pipes and drain rock).
I you plan to amend the soil, a typical soilmixture contains 20 to 40 percent organic
material (compost); 30 to 50 percent clean,
coarse sand; and 20 to 30 percent top soil.
Note: do not add sand to a highly clayey soil.Soils are commonly amended to a depth o
1824 inches.
STEP 4: Determine the sizeo the rain garden
Always check with your local planning department,
public works, or stormwater utility beore design-
ing your rain garden. I your local jurisdiction does
not have a recommended size calculation or a
rain garden, then we recommend the size o the
rain garden be at least 10 percent o the impervi-ous surace draining to the garden. Rain gardens
should ideally be between 6 and 24 inches deep.
To use this number, your soil should drain at least
1/2 inch per hour or greater. Compare the result o
your soil inltration test with the table above, ora good idea o how your soil infuences the size o
the rain garden. Rain gardens o 10 percent and 1/2
inch minimum inltration rate should treat a large
majority o storms in Oregon.
Using the area o impervious surace that you
calculated in Step 1, multiply this by 0.10 (or 10
percent). The result will be the area o the rain
garden in square eet. The calculation is:
Drainage rate Recommendation
Less than 1/2 inch per hour Do not build a rain garden on this site without proessional
assistance.
Between 1/2 and 1 inch/hourLow inltration or a rain garden. Homeowners may want to build
a larger or deeper garden, or likewise plan or additional overfow
during high-rainall storms.
Between 1 and 1 1/2 inches/hourAdequate inltration or a rain garden. Plan or sucient overfow
during high-rainall storms.
Between 1 1/2 and 2 inches/hour Adequate inltration or a rain garden. Plan or sucient overfowduring high-rainall storms.
Faster than 2 inches/hour
High inltration or a rain garden. Design should eature ewer
moisture-loving and more drought-tolerant plants. The rain garden
may also be sized to hold smaller amounts o water, have a deeper
mulch layer, or have denser plantings.
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams12
(Length o surace area x Width o surace area)x .10 = total rain garden area
An example: 30 eet x 12 eet = 360 square eet
x .10 = 36 square eet o rain garden
The more impervious area you want to treat, the
bigger your garden. The size o your rain garden
will also depend on the space available and your
budget. I you dont have enough space, you can
build multiple rain gardens or build a smaller one
and plan or it to overfow more oten.
Note: Rain gardens should be a minimum o veeet wide to accommodate gentle side slopes that
will host plants and minimize soil erosion.
Rain garden depth
Most rain gardens should be between 6 and 24
inches in ponding depth with 24 inches o ad-
ditional depth or saety. This means that rain
gardens range rom 8 to 28 inches in depth. The
table below is a general guide or rain garden pond-
ing depths based on dierent drainage rates. Add
depth where overall size is restricted by setbacks,
structures, vegetation, or other obstacles.
Drainage rate Suggested rain garden ponding depth
Between 1/2 and 1 inch/hour 1224 inches
Between 1 and 2 inches/hour 68 inches
Faster than 2 inches/hour 6 inches
Typical ponding depth624 inches
Figure 8: Pondingsurface is denoted
by the doed line.
(Graphic: EMSWCD)
Note: remember to account or the addition omulch when you plan or your nished depth (see
Mulching on page 23). For example, i you areadding 3 inches o mulch to your nal planted gar-
den and it needs to be at least 12 inches deep, you
must excavate to a depth o 15 inches rom grade.
RAIN GARDEN DICTIONARY:
Thesizeo a rain gardenreers to the volumeo water it can hold beore the water overfows
at the exit point. This volume is described in
terms o ponding depth and square eet o
surace area (depth x width x length).Ponding depth is the depth at which the watercan pond beore it fows out o the rain garden
(see Figure 8). It is measured rom the surace
o the rain garden at its lowest point to the
elevation o the outlet. Rain gardens gener-
ally should range between 6 and 24 inches
in ponding depth, adding 24 inches o extra
depth below the outfow or saety.
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams 1
Dig saely!
Its the law in the state o Oregon to call the Utility
Notication Center by dialing 811 or 1-800-332-2344
beore beginning any excavation. The service is
ree and convenient or homeowners, contractors,
excavators, landscapers, etc. Anyone planning to
dig must contact the Center at least two businessdays prior to digging, in order or the undergroundutilities to be located and accurately marked using
color-coded paint. For more inormation on
digging saely, visit the OUNC Web site:
www.digsaelyoregon.com.
Delineate the rain garden
Use a garden hose, string, stakes, or marking paintto delineate the boundary o the rain garden on the
site. Beore you dig, be sure to note any existing
utilities or vegetation that might be damaged by
digging (see note above).
Getting water to the rain garden
Your garden will not actually be managing storm-
water i it does not collect rain water rom your
homes impervious suraces. That means you
must nd ways to get water rom your collection
points to your garden, sometimes by diggingtrenches, running gutter extenders, or even build-
ing articial streams that run only when the rain
alls. The water may be routed using a pipe, rock
tiles, or other hard suraces, or a small swale (ditch)
lined with rock (3/4-inch diameter, washed drain
rock or pea-sized gravel). I using a pipe, we recom-
mend a 4-inch diameter ABS.
I not using a rock-lined trench, the outlet o the
routed water and inlet o the rain garden should be
lined with rock (again, 3/4-inch diameter, washed
drain rock or pea-sized gravel) to prevent erosion.In addition, a 4-inch-wide strip o grass could be
used to lter and settle sediment rom your rain
water beore it enters the rain garden.
Figures 9a and b: Delineating rain garden boundaries with a garden hose (top)and marking paint (above). (Photos by Robert Emanuel, OSU)
Figure 10: Moving water rom a gutter to a gardencan be as simple as a piece o buried 4-inch drain pipe.
Note that the pipe is buried at least 12 below the
surace as required by Oregons plumbing code. See
note on page 19. Photo:PortlandBureauoEnvironment
alServices
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams14
Figure 13 (right): A dry stream bed conveys water across a surace beore itenters a rain garden. (Photo: Judy Scott, OSU)
Figure 11: Using a rock-lined trench to convey water across a walkway (Photo: Portland Bureau o Environmental Services [BES])
Figure 12: Trench drain through a sidewalk at a building in Portland.(Photo: Derek Godwin, OSU)
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams 1
Disconnecting downspouts
Disconnecting downspouts is an important part
o rain garden construction. Avoid creating saety
and structural problems when disconnecting any
downspouts rom your storm sewer by ollowing
these saety guidelines:
Dont disconnect a downspout in an area that
is too small to drain the water properly.
Disconnected downspouts must be extended
to discharge water at least 6 eet rom a struc-
ture with a basement or 2 eet rom a crawl
space or slab oundation.
Direct water away rom your structure, a retain-
ing wall (by at least 10 eet), a septic drain eld,
or an underground storage tank.
The end o the downspout extension must be
at least 5 eet away rom a neighboring property
and 3 eet rom a public sidewalk. Do not direct
water toward a neighboring property, especially
on a steep slope.
Steps or disconnecting:
1. Measure the existing downspout rom the top
o the standpipe, and mark it at least 9 inches
above the standpipe. A standpipe is the pipeleading into the below-ground storm sewer.
2. Cut the existing downspout with a hacksaw at
the mark. Remove the cut piece.
3. Plug or cap the standpipe. Do not use concrete
or another permanent sealant.
4. Attach an elbow to the newly cut downspout by
inserting the elbow over the downspout. Then
use at least two sheet-metal screws to secure
the two pieces.
5. Measure and cut the downspout extension sothat when it is attached, you will be ollowing
the saety guideline above. Fit the extension
over the elbow and attach it with sheet-metal
screws.
6. I the extension does not connect directly to a
below-ground pipe or lead into a rain garden,
use a splash block or gravel to prevent soil
erosion.
7. Remember that each section should unnel into
the one below it. All parts should be securely
astened together with sheet-metal screws.
Be sure to maintain your gutter system. Inspect
it regularly or leaks, sagging, holes, or other
problems. It is a good idea to annually inspect
and clear debris rom gutters, elbows, and other
connections beore the rains arrive.
This material is condensed rom How to Manage
Stormwater: Downspout Disconnection, City o
Portland Bureau o Environmental Services
publication BS 07011. It is used here with permission
o the City o Portland, BES. The ull document can
be ound at www.portlandonline.com/bes/index.
cm?c=46962&a=188637.
Figure 14. Downspout connected to downspoutextension that directs fow away rom a buildings
oundation. Note sheet-metal screws.(Photo: Robert Emanuel, OSU)
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams16
Designing or overfow
When properly sized, a rain garden is designed
to handle roughly 8090 percent o the water
that alls on a given impervious surace. There-ore, extreme events should be considered when
designing your garden. For this reason, it is critical
to include plans or overfow. This should be a
notch or a pipe in the berm, at least 2 inches lower
than the berm. The overfow could lead to one o
several options:
a fat area in your home landscape where water
can be saely absorbed,
another rain garden,
a French drain or rock-lled soakage trench,
a swale or drainage ditch, or
return stormwater to its original destination be-
ore the rain garden was built (such as a public
sewer, street gutter, storm drain, or pipes and
catch basin).
Be sure to discuss your plans or overfow with
your local planning department. They typically
have specic, approved locations or draining the
overfow o-site. They may also require a permit
or a rain garden.
Figure 15: Curb-cut inlet or a parking lot and an overfow device (pipe andscreen) or a parking lot in Gresham, Oregon. (Photo: Derek Godwin, OSU)
Figure 16: PVC pipe outfow rom a coastal Oregon rain garden. The rocks,mulch, and gravel help protect the area rom erosion. (Photo: Robert Emanuel, OSU)
Figure 17: A rain garden in Gresham, Oregon, llswith rain. Note the use o rocks at the outfow point
near top. (Photo: City o Gresham)
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams 1
Note: For smaller gardens, or gardens in high rain-all areas with soils with low inltration rates, you
will need to take extra care in routing the overfow
away rom the garden in a sae manner.
Keys to success
Permits and design modifcations:Check with your local government (city or county
planning department) to
nd out whether you can legally build a rain
garden (and whether you need a permit)
get inormation on disconnecting downspouts
or routing water o the site
learn about any design requirements or setbacks
You may decide that you need the help o a licensed
landscape proessional or engineer.
Be kind to trees:Its a good idea to avoid placing a rain garden
beneath the drip line o large trees. The tree roots
will be damaged by the excavation and may also be
overwhelmed by the amount o water that pools
beneath them.
When is the best time to build?
The ollowing schedule is recommended to pre-vent soil compaction, maintain the soils ability to
inltrate stormwater, and minimize the need or
watering the plants:
Conduct site assessments and design the gar-
den in the all, winter, and spring when the soil is
wet but not rozen;
Excavate and build the garden when the soil is
dry enough to work with easily; and
Plant vegetation in the all and as early as pos-
sible the ollowing spring.
STEP 5: Constructing a rain garden
Excavation, grading, and berms
Plan to place the spoils to the outside edge o thegarden and away rom the infow point. Use the
spoils and any excess soil amendments to orm
the berm that bounds the rain garden on one
or more sides, depending on the terrain. Berms
should be built to have at least 2 inches o height
above the elevation o the outlet.
Whether digging by hand or machine, excavate
the soil rom the outer edge o the rain garden to
minimize soil compaction.
We recommend that the slope on the rain gardenberm be at least 18 inches o horizontal length to
6 inches o vertical height (3:1) or fatter on both
sides o the berm. I the rain garden is 12 inches in
depth, you will need to have 36 inches o slope on
either side o the berm.
Figure 18: Excavator is located outside o the rain garden in orderto make sure the machine does not compact soil in the rain garden.(Photo: Robert Emanuel, OSU)
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams 1
Note: Oregon State Plumbing Code requires thatany buried utility pipe should be at least 12 below
the soil level starting at the downspout. It also
requires underground plumbing to be a durablematerial such as Schedule 40 ABS or PVC. While
corrugated plastic pipes are requently ound in
rain gardens (including some photographed in this
guide), these materials may not last, especially in
colder climates. I using an infow pipe buried 12
inches deep, a rain gardens nished depth will
need to be between 14 and 18 inches.
To amend or not to amend?
Rain gardens depend on healthy plants and soils
to capture, clean, and lter the stormwater runo.
As mentioned in Step 1, your soils may need to
be amended to ensure strong plant survival and
microbial health. Where possible, your existing soil
should be tilled to 18 to 24 inches deep i amend-
ing with compost, topsoil, or sand. See note on
page 20.
Figure 24: An outfow notch in a Portland, Oregon, rain garden, protected byrock to prevent soil erosion. (Photo: Robert Emanuel, OSU)
Figure 22: Four-inch ABS pipes here will convey waterrom this building into a rain garden. Pipes like these
must be graded to drop about 1 inch or every 10 eet
so water fows away rom the building but does not
build up too much velocity by the time is arrives in the
rain garden. (Photo: Robert Emanuel, OSU)
Figure 23: The point where water enters a rain garden should be well armoredwith rock and plants (beach strawberries here) to prevent erosion.(Photo: Robert Emanuel, OSU)
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams20
STEP 6: Choose the right plantor the right place
Fertilizers and pesticides oten contribute to storm-water pollution in streams and lakes. Since rain
gardens are designed to treat stormwater runo, it
is very important to choose plants that can survive
and thrive without chemical inputs. It is also good
practice to choose plants and design your garden to
require minimal to no extra water.
Planting zones and plant selection
Plants vary in their tolerance o certain conditions,
such as shade, fooding, moisture, and cold tem-
peratures, while maintaining their ability to surviveand grow. Rain gardens have zones that vary in
wet and dry conditions and possibly sunlight and
shade; thereore, plants need to be selected based
on their tolerance to these conditions and placed
in the corresponding zone to survive and thrive.
Furthermore, plants need to be chosen based on
their ability to survive in the climate relative to the
region in Oregon in which they are planted (that is,
Willamette Valley, coast, southwest, central, and
east). Rain gardens are generally meant to be low
maintenance.
Compost
Compost helps the soil hold moisture, increase
microbial activity, improve its ability to lter and
adsorb pollutants, and increase plant survival in therst ew years as it slowly biodegrades. Be sure to
use weed-ree mixes.
!Note: Rain garden plants do not have to be wet-land or water plants. In act, they should be able to
tolerate drying out or long periods with little to no
supplemental irrigation, depending on where you
live in Oregon and how long the plants have been
established.
Rain gardens can be divided into three zones, rela-tive to their wet and dry conditions: moist, moderate
and dry. I you select plants rom the lists provided in
this guide, be sure to pay attention to their designa-
tion as tolerant o moist, moderate, and dry
soil conditions. Use plants that are designated as
doing best in moderate and dry conditions only
on the slopes or otherwise dry parts o the garden.
Do not put a plant that cannot tolerate wet eet in
the bottom or wettest part o your garden, because it
could drown during rainy periods.
Soil type will also infuence the plants and the sizeo dierent moisture zones. For example, rain gar-
dens built in high-clay or slow-draining soils should
be planted with more plants that tolerate wet
eet, while rain gardens in sandy or ast-draining
soil can be planted with more dry-adapted plants
(listed here with moderate or dry designations)
In ast-draining rain gardens, group your moisture-
loving plants within a ew eet o the infow points.
Figure 25: Rock, gravel, and sedges protect the infow point in a rain garden.(Photo: Chris LaBelle, OSU)
RAIN GARDEN DICTIONARY:
Zones o wet and dry conditions
Moist: plant preers moist soil and toleratesdry soil other times o the year.
Moderate: plant can tolerate moist and drysoils equally.
Dry: plant tolerates and even thrives in drysoil during most o the year.
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams 2
Filling up the rain garden and watching it drain
several times will help you visualize where water
pools and where it drains quickly. This will help
you choose the right plant or the right place.
Visit local examples o rain gardens to get ideas
o what plants thrive and how the design works
in your local area.
Because this guide was written with most o Or-
egon in mind, we recommend that gardeners use
the lists and designs provided here as suggestions,
not as ironclad rules to ollow. Be creative, and be
prepared to experiment with the garden; garden
areas and conditions are always variable, and no
design is ail-sae.
Remember that plants can do some o the work
to make a rain garden easier to maintain. Some
especially tough plants, such as sedges or bunch
grasses, should be grouped around eatures likeinfow and outfow points, to slow down water
as it enters the rain garden. Use groundcovers
on berms and other areas where erosion is a
concern. Several designs are suggested on pages
2835.
!The area around your infow will retain the most
moisture in your rain garden, meaning that what
you plant there must be the most tolerant o moist
soil.
Figure 26: Planting zones refect the areas where the garden will have the most and least water when fooded, aswell as during the dry season. The graphic on the let illustrates the topographic zones o the rain garden, the
graphic on the right illustrates zones o high and low soil moisture during the dry season. (Graphic: Robert Emanuel, OSU)
Figure 27: Planting zonesin this cross section illustrate
where soil will be moist
during the wet season.(Graphic: EMSWCD)
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams22
Key plant characteristics
Other plant characteristics and plant selectionWhile rain gardeners should ocus on selecting
and placing plants that may tolerate more or lesswater, there are other characteristics to note.
Remember, rain gardens can and should be attrac-
tive eatures in your landscape, rather than just
places to treat stormwater. Other characteristics to
consider include:
What is the plants height and width?
Does the plant have attractive oliage, fowers, or
ruit?
Does it attract benecial insects and wildlie?
Does it look good with neighboring plants andlandscape?
Seasonality
Shade tolerance
Temperature requirements
! Remember that plants grow! This simple act
should keep you rom overplanting your rain gar-
den or placing plants too close together. Respect
their ultimate size requirements and keep in mind
that these vary throughout Oregon.
Planting tips
When planting, be sure to dig a planting hole at
least as big as the pot, i the soil has been amend-
ed. I you are planting into unamended soil, dig
a hole that is at least twice the diameter but the
same depth as the pot. Most native and nonna-
tive plants need to be planted at the same depth
as they were growing in their pots. Leave some
compost and soil mixture mounded at the bottom,
as appropriate, to keep your plant at the same level
as it was in its original container.
Careully remove the plant rom its container. I the
plant roots have ormed a solid mass around the
outside o the pot, gently loosen them or careully
score the outside layer with a sharp knie. Lower the
root ball into the planting hole slowly, to prevent
cracking or breaking o the soil around the roots.
I the root ball was opened up, spread some o the
roots over the mound in the center o your hole.
Backll your hole with well-drained soil rich in
compost, being careul to make sure you do not
cover the crown o the plant i it was exposed in
the original container. Be sure to rm the soilaround the plant and water well with a slow stream
o water or soaker attachment.
A note aboutinvasive species
Invasive plants such as
English Ivy, Japanese
knotweed, spurge laurel,
or butterfy bush cost Oregonians millions
o dollars in control, prevention, and directeconomic losses. An invasive plant is one that
escapes cultivation and multiplies in other
habitats, to the near exclusion o species that
would occur naturally.
Gardens and gardeners are among the most
important pathways or invasive plants to
move into new places. You can help stop
the biological invasion by eliminating known
invasive plants rom your garden; preventing
the introduction o new, aggressive plants;
and replacing nonnative invaders with riendlynative plants in your landscape.
For common invasive plants to avoid as well
as some excellent alternatives, consult the
publication GardenSmart Oregon, available at
www.oregoninvasivespecieshotline.org and
through your local Soil and Water Conserva-
tion District or OSU Extension Service oce.
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams 2
Mulching
Mulch is another important part o the rain
garden. It will help shade the soil and keep it cool
and may increase soil moisture during the drysummer and all months. The right mulch can also
help control weeds. More importantly, microbial
activity in the mulch helps to break down some
o the common pollutants in stormwater. For this
reason, we recommend always applying mulch to
new rain gardens and maintaining some mulch in
established ones.
Double-shredded conier bark mulch (also known as
bark dust) is probably the most commonly used
in landscape plantings in the Pacic Northwest.
Douglas-r and hemlock are the most commonly
sold barks, although pine bark is also available. Bark
mulch is available in a range o grades, rom ne
through medium to large bark nuggets. We recom-
mend using ne-grade bark mulch rather than nug-
gets, as the latter will foat. We do not recommend
using sawdust or grass clippings, as these materials
will alter your soil chemistry and can aect the abil-
ity o the garden to support healthy plants.
Apply mulch at a rate o 23 inches evenly across
the rain garden on the edges or slopes o your raingarden. I you choose not to use bark mulch in the
lowest point o the garden, then be sure to apply a
2- to 3-inch depth o compost instead.
Rocks and gravel are oten used at infow and outfow
areas to dissipate energy rom water and prevent
erosion. They will also make maintenance in the rain
garden easier. Rock and gravel are important design
elements that can add interest to the rain garden.
Washed pea gravel is an attractive small-grade rock
or use in the base o the rain garden.
Compost is another alternative or covering the
base o the rain garden. It will not suppress weeds
as well as wood chips or other materials, but it will
succeed in adding ertility to the soil and in lter-
ing pollutants. More nely textured compost is
less likely to foat in heavy rains. Apply compost at
the same rate as indicated in the chart to the right.
How much mulch?
To calculate the total cubic yards o mulch needed
or your rain garden project, ollow these steps:
1. Multiply the length o your rain garden by the
width to nd the square ootage.
2. Multiply that square ootage by 0.25, which will
equate to 3 inches o mulch.
3. Divide that value by 27 to yield cubic yards o
mulch needed or your project.
The steps above can be used to quickly estimate
the necessary amount o mulch to purchase based
on various depths o mulch. Remember not to
pile mulch alongside the stem o plants. Mulch
is moist and can lead to rotting around the stem.Also, remember to break up any mulch that may
be dry or clumped together as you spread it over
your rain garden.
For more inormation on mulches, please consult:
Bell, N., D. M. Sullivan, and T. Cook. 2009. Mulch-
ing Woody Ornamentals with Organic Materials.
EC 1629-E. extension.oregonstate.edu/catalog/pd/
ec/ec1629-e.pd
Cubicyards omulch
Rain garden square eet andmulch coverage based on depth
1 2 3
1 338 sq. t. 158 sq. t. 108 sq. t.
2 676 sq. t. 316 sq. t. 216 sq. t.
3 1,014 sq. t. 474 sq. t. 342 sq. t.
4 1,352 sq. t. 632 sq. t. 432 sq. t.
5 1,690 sq. t. 790 sq. t. 540 sq. t.
6 2,028 sq. t. 948 sq. t. 648 sq. t.
7 2,366 sq. t. 1,106 sq. t. 756 sq. t.
8 2,704 sq. t. 1,264 sq. t. 864 sq. t.
9 3,042 sq. t. 1,422 sq. t. 972 sq. t.
10 3,380 sq. t. 1,580 sq. t. 1,080 sq. t.
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams24
Watering a rain garden
Even ater you have chosen and careully planted
the right plant in the right place and mulched
the garden, it is important to make sure new plantsget sucient water during their rst and possibly
second dry summer season, until they are ully
established. This is especially true i the rain garden
was planted in the spring or summer.
As with any watering regime, water deeply and
slowly during the coolest time o the day (evenings
i possible). Soaker attachments or soaker hoses
are particularly useul or this purpose. Use a soil
probe or stick to check whether moisture is pres-
ent in the rain garden at a depth greater than 23
inches.
Ater the rst or second dry season, depending
upon how good the plants look and how hardy they
are, you may be able to stop watering altogether
and depend on rain entirely. Remember that the
more native plants you use in your rain garden and
landscape, the less supplemental water youll need
to apply during drought periods.
STEP 7: MaintenanceWeeding, pruning, and mulching
You will need to weed your rain garden during the
rst couple o years. Try to get out all the roots o
the weedy plants. Weeds may not be a problem in
the second season, depending on the variety and
tenacity o weeds present. In the third year and
beyond, the grasses, sedges, rushes, shrubs, trees,
and wildfowers will begin to mature and should
out-compete most o the weeds. Weeding isolated
patches might still be necessary on occasion.
Be sure to maintain the rain garden plants in
whatever ashion satises you the mostas a
wild-looking garden, a more manicured space,
or something in between. Plants may need to be
pruned as appropriate or the look you desire in
your garden.
Maintain the organic mulch layer in your rain gar-
den by replenishing it when needed. Apply mulch
Figure 28: A rain garden that is mulched with gravel rather than bark.
(Photo: Portland BES)
Figure 29: Gravel, rocks, and even dritwood add to the interest in this raingarden. The pea gravel also acts as mulch, helping to retain soil moisture while at
the same time minimizing erosion. (Photo: Robert Emanuel, OSU)
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams 2
to a 2-inch depth on bare soil. I your rain garden
receives any sediment or soil eroded rom other
locations in your landscape, you may need to cleanthis out on occasion. It is important also to keep
exposed the rocks, tiles, or other hard suraces you
placed in the rain garden to slow water at the infow
and outfow points, so that they can continue to
slow down water and prevent erosion.
Depending upon the local climate and plant choice,
plants may need supplemental water during the
summer. This is especially true in eastern, cen-
tral, and southern Oregon. The use o native and
drought-tolerant plants will help reduce the amount
o supplemental irrigation during dry periods.
Figure 30 (above): A newly established rain garden in Gresham, Oregon (Photo: City o Gresham).
Figure 31 (right): This Willamette Valley rain gardenis planted with Autumn Joy Sedum (Sedum
telephium), slough sedge (Carex obnupta), New
Zealand sedge (Carex testacea), yellow-eyed grass
(Sisyrinchium caliornicum) and mallow (Malva spp.).
(Photo: Chris LaBelle, OSU)
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams26
Dont drown your plants!
Another consideration is to make sure your plants
in the base dont drown in their rst winter. Plants
need air in the soil, so when the rain garden staysconsistently fooded or long, wet winters, it may
become necessary to notch the berm at the outlet
to a lower elevation or add more notches to the
berm. This will help the rain garden drain a little
aster and give the plants a chance to establish
healthy roots. Ater the rst winter, ll in the notch-
es and allow it to unction normally. Some proes-
sionals and gardeners even advocate diverting
stormwater rom the rain garden or the rst year or
two while plants become established, especially in
heavy soils.
A note about Oregons regions
Oregon is a much more geographically diverse stat
than most. Climates and soils can vary signicantly
between the coast, Willamette Valley, Cascades,
eastern high desert, and southwestern mountains.
Below are a ew tips on region-specic items to be
aware o in designing, building, or maintaining a
rain garden.
Willamette Valley:
Most o the materialsincluding many o the plant
selections in this guidewill help rain gardeners
in the Willamette Valley. With its generally mild
seasons, good soils, and mostly fat territory, the
Willamette Valley presents ew obstacles or raingardeners. When planning your rain garden or the
Willamette Valley, keep these things in mind:
Summertime temperatures can occasionally
exceed 90 degrees; thus, some plants in sunny
locations with ast-draining soils will need supple
mental irrigationat least or the rst two or
three years while roots are becoming established
Wintertime temperatures in some locations can
drop well below reezing and thus create prob-
lems or more tender or sensitive plants. It is
important to choose plants adapted to both summer and winter conditions in your area.
The Willamette Valley contains the states bigges
cities, each o which may have their own require-
ments or on-site stormwater management
(and rain gardens). I you live in Salem, Eugene,
Gresham, or Portland, contact your local govern-
ment or more inormation.
Coastal Oregon:
With the infuence o strong Pacic winds, abun-
dant rainall, and generally milder temperatures, thcoast can be challenging or rain gardeners but also
presents some great opportunities. When planning
your rain garden on the coast, keep these things in
mind:
Strong winds can dry out and damage plants any
time o the year, especially or gardens located
near the beach. Provide or shelter, or plan your
plant selections to take account o the wind dam
age. Additional water may be necessary during
Figure 32: A rain garden in Portland, Oregon. (Photo: Portland BES)
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams 2
the summer months, when drying winds can be
most damaging or newly established rain garden
plants.
On the Oregon coast, rainall is very abundant.Where coastal soils drain at less than 1 1/2 inches
per hour, size the rain garden to at least 15
percent o the impervious surace. For example,
a rain garden is designed to capture runo rom
a 300-square-oot surace. Hence, the calcula-
tion is 300 x .15 = a 45-square-oot rain garden.
Consult our online materials at extension.
oregonstate.edu/watershed/rain-gardens or
more inormation on using the modeling
method to size your rain garden or your soil
and precipitation.
Some beach homes are built on ossilized sand
dunes. Soils on and around these geologic ea-
tures will drain extremely rapidly, oten in excess
o 2 inches per hour, making a rain garden unnec-
essary or impractical. Furthermore, the additional
water rom a rain garden built on a ossilized
dune may cause it to slump or even collapse. We
do not recommend constructing a rain garden
under these conditions.
Southwestern, central, and easternOregon:
Gardening in southwestern, central, or eastern
Oregon can be rewarding but has its own set o
challenges. These arid and semi-desert regions are
characterized by volcanic, rocky, or clay soils, and
steep slopes. And i that isnt enough, many gar-
deners must balance these restrictions with hungry
deer and the reality o living in a wildre-prone area.
When planning your rain garden or either region,
keep these actors in mind:
I you live in a re-prone area, avoid using plantsin your rain garden that are fammable. Plants
with dry material (such as leaves or needles)
and those with ne structure, aromatic leaves,
loose bark, or resinous sap tend to be fammable.
Consult the Extension publication Fire-ResistantPlants or Oregon Home Landscapes or moreinormation and a list o re-resistant plants
(available online at extension.oregonstate.edu/
emergency/FireResPlants.pd or by visiting your
local OSU Extension Service oce).
These semi-arid regions have long, dry summers
with very little rainall. Depending on your plant
choice, it may be necessary to irrigate your rain
garden two to three times each summer to keep
the plants healthy, attractive, and re-resistant.
I deer plague your garden, use rain garden plants
that are also deer-resistant. Although ew plants
are truly deer-resistant in every situation, mostnurseries can provide a list o plants that deer
tend to avoid.
Central and eastern Oregon winters are longer
and colder than in other areas o Oregon. Plants
may not establish new roots well in rozen soils.
Plan to construct and plant your garden early
enough in the late summer to allow or plants
to become established. Native plants that can
handle the annual swings in temperature will
survive best in a low-care rain garden.
I you live in a location with ast-draining volcanicsoils, you might want to make your rain garden
shallower or smaller, depending on your space
constraints or needs. Consult our online materi-
als at extension.oregonstate.edu/watershed/
rain-gardens or more inormation on using the
modeling method to size your rain garden or
your soil and precipitation.
Figure 33: Rain garden at Astor Elementary Schoolin Portland, OR. (Photo: Candace Stoughton, EMSWCD)
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams28
yr SS
gr
dr
pc
Os
Dr
Ds
cr
Gc
Drlp
CENTRAL OREGON SUN
Abbr. Common name Scientifc name Qty.
SS Smooth sumac Rhus glabra 1Ds Douglas spiraea Spiraea douglasii 3Dr Dwar redtwig dogwood Cornus sericea Kelseyi 11Gc Golden currant Ribes aureum 1Os Oceanspray Holodiscus discolor 1gr Canada goldenrod Solidago canadensis 13cr Common rush Juncus eusus var. pacicus 22dr Dagger-lea rush Juncus ensiolius 13lp Large-lea lupine Lupinus polyphyllus 13pc Purple conefower Echinacea purpurea 6yr Yarrow Achillea milleolium 9
Sample Rain Garden Layouts
These sample rain garden layouts use plants suitable
or the states dierent regions. Consider whether
you want your garden to be ormal, inormal, round
or square. Use these designs to give you ideas or
how to incorporate dierent types o plants into the
wetter and drier zones o your rain garden.
The abbreviations used will help you see at a glance
which type o plant is being reerenced. Two capital
letters denote a tree; a capital and lower-case com-
bination denotes a shrub; and two lower-case letters
mean the plant is a perennial, rush, sedge, or grass.
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams 2
NBcr
Dr
Tg
wf
SuBh
th
Dr
Mo
wf
CENTRAL OREGON SHADE
Abbr. Common name Scientifc name Qty.
NB Pacic ninebark Physocarpus capitatus 1Bh Black huckleberry Gaylussacia baccata 4Dr Dwar redtwig dogwood Cornus sericea Kelseyi 8Su Gro-low sumac Rhus aromatica Gro Low 1Mo Mock orange Philadelphus lewisii 1Tg Tall Oregon grape Mahonia aquiolium 3cr Common rush Juncus eusus var. pacicus 13th Tuted hairgrass Deschampsia caespitosa 20w Western escue Festuca occidentalis 10
Sample Rain Garden Layouts
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams30
yr
sr
Tg
Fc
nzNr
Tg
yr
th
PC
sr
Sample Rain Garden Layouts
SOUTHWEST OREGON SUN
Abbr. Common name Scientifc name Qty.
PC Pacic crabapple Malus usca 1Fc Flowering currant Ribes sanguineum 3Nr Nootka rose Rosa nutkana 3Tg Tall Oregon grape Mahonia aquiolium 6nz New Zealand sedge Carex testacea 14sr Spreading rush Juncus patens 6th Tuted hairgrass Deschampsia caespitosa 8yr Yarrow Achillea milleolium 12
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams 3
SOUTHWEST OREGON SHADE
Abbr. Common name Scientifc name Qty.
CA Cascara Rhamnus purshiana 1Bt Black twinberry Lonicera involucrata 6Eh Evergreen huckleberry Vaccinium ovatum 8Nr Nootka rose Rosa nutkana 6Tg Tall Oregon grape Mahonia aquiolium 2lp Large-lea lupine Lupinus polyphyllus 2sb Santa Barbara sedge Carex barbarae 16wg Wild ginger Asarum caudatum 12
Sample Rain Garden Layouts
Eh
CA
Eh
sb
lp
wg
Tg
Nr
Tg
wg
BtBt
lp
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams32
WILLAMETTE VALLEY SUN
Abbr. Common name Scientifc name Qty.
SA Sitka alder Alnus viridis ssp. sinuata 1Bh Baldhip rose Rosa gymnocarpa 6Ro Red osier dogwood Cornus sericea 3Rm Rosemary Rosemarinus ocianalis 4dr Dagger-lea rush Juncus ensiolius 25tt Taper-tipped rush Juncus acuminatus 10w Western escue Festuca occidentalis 6
Sample Rain Garden Layouts
Rm
wf
Ro
SA
tt
Bh
dr
Bh
Bh Bh
Bh
wf
Ro
Ro
Rm
Rm
Bh
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams 3
WILLAMETTE VALLEY SHADE
Abbr. Common name Scientifc name Qty.
VM Vine maple Acer circinatum 1Dg Dull Oregon grape Mahonia nervosa 14Dr Dwar redtwig dogwood Cornus sericea Kelseyi 9Sb Snowberry Symphoricarpus alba 3ds Dense sedge Carex densa 13br Small-ruited bulrush Scirpus microcarpus 11
Sample Rain Garden Layouts
Dg
Dr
br
Sb
ds
Dg
VM
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams34
OREGON COAST SUN
Abbr. Common name Scientifc name Qty.
PW Pacic willow Salix lucida ssp. lasiandra 1Es Dwar escallonia Escallonia Newport Dwar 4St Silktassel Garrya elliptica 1cs Curly sedge Carex rupestris 32oi Oregon iris Iris tenax 11sl Spanish lavender Lavandula stoechas 13s Sword ern Polystichum munitum 3
Sample Rain Garden Layouts
cs
Essl
sl
St sf
oi Es
PW
oi
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams 3
OREGON COAST SHADE
Abbr. Common name Scientifc name Qty.
IP Indian plum Oemleria cerasiormis 1Bb Blue-ridge blueberry Vaccinium pallidum 3Cl Common lilac Syringa vulgaris 1Dr Dwar redtwig dogwood Cornus sericea Kelseyi 6cr Common rush Juncus eusus var. pacicus 8bh Pacic bleeding heart Dicentra ormosa 13ss Slough sedge Carex obnupta 13s Sword ern Polystichum munitum 6
Sample Rain Garden Layouts
Bb
bhIP cr
Dr
ss
bh
bh
Clsf
sf
Dr
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Rain Garden Plant List: Trees and Shrubs
CommonN
ame
ScientifcName
OregonNa
tive
Willamette
Valley
Coast
Central/Eas
t
Southwest
Moisture
Zone
SunRequirements
Height
Width
Plant
Characteris
tics
Vine mapleAcer circinatum
Y X X X Xmoderate,
dryshade/
part1520' 1520'
Small, multi-stemmed tree,red-orange all color,excellent soil binder
Sitka alder
Alnus viridis ssp.sinuata
Y X X X wet,moderate ull/shade 315' 1015' Fixes nitrogen in soil
Red osierdogwoodCornus sericea
Y X X X Xwet,
moderate,dry
ull/part 48' 48'Red twigs provide winterinterest, white fowers insummer
Dwar redtwig
dogwoodCornus sericeaKelseyi
Y X X X X
wet,
moderate,dry
shade/ull 2' 2'
Red twigs provide winter
interest, white fowers insummer
Dwar escalloniaEscalloniaNewport Dwar
N X X Xmoderate,
drypart 3' 4'
Evergreen, fowers in latesummer, ragrant
SilktasselGarrya elliptica Y X X dry ull 612' 612'
Evergreen, fowers in spring,berries attract wildlie
BlackhuckleberryGaylussaciabaccata
N X Xwet,
moderate,dry
shade/ull
13' 3'Flowers in summer, edibleberries, likes acidic soil
The Oregon Rain Garden Guide: Landscaping for Clean Water and Healthy Streams36
TREES AND SHRUBS
JimPollock
BrentMiller
LindaMcMahan,
OSUExtension
TeresaHuntsinger
RebeccaGebeshuber
PeteVeilleux
MarielleAnzelone
See page 20 or tips on choosing rain garden plants. Note that plant size will vary by location.Consult your nursery or OSU Extension Service oce or locally accurate size inormation.
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CommonName
ScientifcName
OregonNative
WillametteValley
Coast
Central/East
Southwest
Moisture
Zone
SunRequirements
Height
Width
Plant
Characteristics
Ocean spray
Holodiscusdiscolor
Y X X X X moderate,dry
ull/part 48' 36'
Flowers in summer,
attractive to wildlie, goodsoil binder
Spanish lavendarLavandulastoechas
N X X Xmoderate,
dryull 1' 12'
Evergreen, pleasantragrance, attractive summerfowers
Black twinberry
Lonicerainvolucrata
Y X X X X wet,moderate part 7' 10'
Yellow fowers in summer,
black berries with bright redbracts, attractive tohummingbirds
Tall OregongrapeMahoniaaquiolium
Y X X X Xmoderate,
dryull/part 4' 4'
Evergreen, yellow fowers inspring, bronze all color
Dull Oregon
grapeMahonia nervosa
Y X X X Xmoderate,
dryshade/
part 2' 2'Evergreen, yellow fowers inspring, berries attract wildlie
Pacic crabappleMalus usca
Y X X Xwet,
moderateull/part
1030'
1030'
Flowers in spring, attractiveto wildlie
Indian plum
Oemleriacerasiormis
Y X X X
wet,
moderate,dry
part 10' 5'
Flowers very early spring,
ragrant leaves, suckeringhabit
Mock orangePhiladelphuslewisii
Y X X X Xmoderate,
drypart 5' 3'
Fragrant fowers attractbirds, butterfies, and bees,prune to shape
3The Oregon Rain Garden Guide: Landscaping for Clean Water and Healthy Streams
Trees and Shrubs
M.S.Yamasaki
EddRussell
KarenHaard
SteveMatso
n
MateAdamkovics
PeteVeilleux
PeteVeilleux
arrowlakelass@fickr
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CommonName
ScientifcName
OregonNative
WillametteValley
Coast
Central/East
Southwest
Moisture
Zone
SunRequirements
Height
Width
Plant
Characteristics
Pacic Ninebark
Physocarpuscapitatus
Y X X X X wet,moderate
ull/part 613' 613' Unique shredding bark,drought tolerant
CascaraRhamnuspurshiana
Y X X X moderateshade/
ullto 20' to 15'
Shrub or small tree, yellowall color
Grolow sumac
Rhus aromaticaGro Low
N X X moderate,dry ull/part 2' 68' Fragrant, orange-red allcolor
Smooth sumacRhus glabra
Y X X X X dryshade/
ull612' 10'
Orange-red all color,suckering habit
Golden currantRibes aureum Y X X
wet,moderate ull 68' 68'
Frangrant spring fowers,edible ruits
FloweringcurrantRibes sanguineum
Y X X Xwet,
moderate,dry
ull/part 10' 7'Showy, pink fower clustersin spring, attractive to birds
Baldhip roseRosa gymnocarpa Y X X X X
wet,
moderate,dry
ull/part 23' 3' Flowers in summer
Nootka roseRosa nutkana
Y X X X Xwet,
moderate,dry
shade/ull
5' 5'Large, ragrant, showyfowers in late spring, bewareo thorns
Trees and Shrubs
The Oregon Rain Garden Guide: Landscaping for Clean Water and Healthy Streams38
DougWaylet
t
LindaMcMahan,
OSUExtension
PeteVeilleux
PeteVeilleux
PortlandBureauo
EnvironmentalServices
KarliScott
JohnHagstrom
LindaMcMahan,
OSUExtension
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CommonName
ScientifcName
OregonNative
WillametteValley
Coast
Central/East
Southwest
Moisture
Zone
SunRequirements
Height
Width
Plant
Characteristics
Rosemary
Rosmarinusofcianlis
Y X X X dry ull 3' 3'
Evergreen, fowering begins
in winter, resh or driedleaves used in cooking
Pacic willowSalix lucida ssp.lasiandra
Y X X X Xwet,
moderateull 13' 10'
Male and emale catkins areborne on separate plants
Douglas spirea/
hardhackSpirea douglasii
Y X X X X
wet,
moderate,dry
ull/part 5' 5' Pinkish fower clusters insummer
SnowberrySymphoricarpusalba
Y X X X Xmoderate,
dryshade/
ull6' 4'
Flowers in spring, whiteberries provide winterinterest, excellent soil binder
Common lilacSyringa vulgaris N X X X
moderate,dry ull/part 15' 612'
Showy, ragrant lavenderfowers in late spring
EvergreenhuckleberryVacciniumovatum
Y X X Xmoderate,
drypart to 9' to 8'
Evergreen, edible berries inlate summer, new growthemerges bronze in color,requires acidic soil, prune toshape
Blue ridgeblueberryVacciniumpallidum
N X Xmoderate,
dryshade/
ull 23' 23' Edible berries
Trees and Shrubs
The Oregon Rain Garden Guide: Landscaping for Clean Water and Healthy Streams 3
NOTES:
OregonEnvironmental
Council
NewYorkBo
tanical
Garden
OSUExtension
BruceM.Marshall
NealKramer
OSUExtensio
n
VictorFarinelli
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CommonN
ame
ScientifcName
OregonNa
tive
Willamette
Valley
Coast
Central/Eas
t
Southwest
Moisture
Zone
SunRequirements
Height
Width
Plant
Characteris
tics
YarrowAchilleamilleolium
Y X X X Xmoderate,
dryull 2' 2'
Summer fowers,spreads by rhizomes
Wild ginger
Asarumcaudatum
Y X X X X moderate shade/part 10" spreading Evergreen, pleasantragrance
Pacic bleedingheartDicentra ormosa
Y X X X Xmoderate,
dryshade/
part2' 2'
Delicate oliage withattractive spring fowers
Purple
conefowerEchinaceapurpurea
N X X X X moderate,dry ull 3' 2' Summer fowers,attractive to wildlie
Oregon irisIris tenax
Y X X Xwet,
moderate,dry
ull 1' spreadingEvergreen, grassyoliage, showy springfowers
Large-leavedlupineLupinuspolyphyllus
Y X X X Xmoderate,
dry ull/part 3' 2'Showy spring fowers,xes nitrogen
Sword ernPolystichummunitum
Y X X X moderateshade/
ull3' 3'
Shiny, leathery,evergreen leaves
Rain Garden Plant List: Perennials
PERENNIALS
The Oregon Rain Garden Guide: Landscaping for Clean Water and Healthy Streams40
JordanMeeter
OSUExtension
JonSullivan
PeteVeilleux
OSUExtension
MichaelG.Sh
epard
FransSchmit
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CommonName
ScientifcName
OregonNative
WillametteValley
Coast
Central/East
Southwest
Moisture
Zone
SunRequirements
Height
Width
Plant
Characteristics
Canada
GoldenrodSolidagocanadensis
Y X X X X moderate,dry
ull 3' 2' Pyramidal fower clustersin late summer
Santa Barbara
sedgeCarex barbarae
Y X wet,moderate ull/part 13' spreading Evergreen, fowers insummer
Dense sedgeCarex densa
Y X X Xwet,
moderateshade/
ull2' spreading
Evergreen, good orerosion control, trappingsediment and slowing thefow o water
Slough sedgeCarex obnupta Y X X X X wet ull/part 25' spreading Excellent soil binder
Curly sedgeCarex rupestris
N X X X wetshade/
ull14" spreading Evergreen
Orange New
Zealand sedgeCarex testacea
N X X Xwet,
moderate ull 25' 1'
Light green leaves
develop red/orangehighlights
Tuted hair grassDeschampsiacaespitosa
Y X X X Xwet,
moderateull/part 2' 3'
Attractive throughoutwinter
Perennials
RUSHES, SEDGES, AND GR ASSES
4The Oregon Rain Garden Guide: Landscaping for Clean Water and Healthy Streams
MartinVavrk
ClaudiaVieira
PeteVeilleux
PatrickStandi
sh
Dr.DeanWm.Taylor,
JepsonHerbarium
PeteVeilleux
PeteVeilleux
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Rushes, Sedges, and Grasses
CommonName
Scientif
cName
Oregon
Native
WillametteValley
Coast
Central/East
Southw
est
Moistu
re
Zone
SunRequirements
Height
Width
Plant
Charac
teristics
Western escueFestucaoccidentalis
Y X X X Xmoderate,
drypart 13' 13'
Inconspicuous yellowfowers and brown seeds.Short-lived (20 years)
Taper-tippedrush
Juncusacuminatus
Y X X X X wet ull/part 3' spreading Drought tolerant
Common rushJuncus eususvar. pacifcus
Y X X X Xwet,
moderateull/part 35' spreading
Tolerant o pollutedconditions. Note thatEuropean sot rush (J.eusus var. eusus) canbe invasive. Please usethe native Pacic variety.
Dagger-lea rush Juncus ensiolius
Y X X X X wet ull/part 2' spreadingFlattened stems muchlike an iris
Spreading rushJuncus patens
Y X X X X wet ull/part 2' spreading Bluish-green oliage
Small-ruitedbulrushScirpus
microcarpus
Y X X X X wet ull/part 4' spreading Good soil binder
The Oregon Rain Garden Guide: Landscaping for Clean Water and Healthy Streams42
SteveMatson
PortlandBureauo
EnvironmentalServices
DenisBousquet
KeirMorse
RobertH
.Mohlenbrock,
USDAN
RCS
PortlandBureauo
EnvironmentalServices
NOTES:
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The Oregon Rain Garden Guide: Landscaping or Clean Water and Healthy Streams 4
For more inormation:
OSU Water and Watershed Education:
extension.oregonstate.edu/watershed/
rain-gardens
East Multnomah Soil and Water Conservation
District: www.emswcd.org
Jackson Soil and Water Conservation District:
www.jswcd.org
Oregon Environmental Council:
www.oeconline.org/stormwater
Andreoletti, Jessica. 2008. The Vermont RainGarden Manual: Gardening to Absorb theStorm. Winooski Natural Resources Conser-vation District. www.vacd.org/winooski/
winooski_raingarden.shtml
Bannerman, Roger, and Ellen Considine.
2003. Rain Gardens: A How-to Manual orHomeowners. UWEX Publication GWQ0371-06-5M-100-S. University o Wisconsin Exten-
sion. clean-water.uwex.edu/pubs/pd/home.
rgmanual.pd
Dunnett, Nigel, and Andy Clayden. 2007. Rain
Gardens: Sustainable Rainwater Management
or the Garden and Designed Landscape.
Timber Press.
Giacalone, Katie 2008. Rain Gardens:A RainGarden Manual or South Carolina. CarolinaCLEAR, Clemson University Public Service.
www.clemson.edu/public/carolinaclear/
Hinman, Curtis. 2008. Rain Garden Hand-book or Western Washington Homeowners.Washington State University Extension.
www.pierce.wsu.edu/Water_Quality/LID/
Raingarden_handbook.pd
Figure 34: Rain garden using a grassy swale as the base. (Photo: Candace Stoughton, EMSWCD)
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Oregon Sea Grant
Corvallis, Oregon
ORESU-H-10-001