Adding a Rain Garden to Your Landscape

1. Landscapes for Maine
PHOTO: EDWIN REMSBERG, USDA-CSREES
Adding a Rain Garden
to Your Landscape
Bulletin #2702
What Is a Rain Garden longer running over the surface
of the land, it cannot transport
complement any home style, as
there are many choices of shapes
and Why Would You pollutants to nearby streams via and plants that can be
surface runoff or storm drains. incorporated into your garden.
Want One? Rain gardens are easy and Rain gardens can even attract
A rain garden is a depression inexpensive to install and birds and butterflies!
in the ground that is planted with maintain. Since they are flexible
water-loving native perennials and in size, shape, and appearance,
Do rain gardens harbor
shrubs. Water from a downspout they can fit into almost any mosquitoes?
or other source flows into the rain landscape and lifestyle.
A properly constructed rain garden
garden, where it soaks into the Rain gardens are beautiful will drain water, not hold it. In a
ground and is used by the plants. well-designed rain garden, water
In addition to adding beauty will soak into the ground in a day.
Rain gardens make sense to lawn areas with height and Mosquitoes will not survive in
color, rain gardens can replace areas that dry out in seven days
Rain gardens help protect the or less after a summer rain,
water quality in our lakes, streams, lawn areas, which would because the development of a
and rivers by reducing the amount otherwise need mowing, with an mosquito from egg to adult takes
of polluted runoff reaching these interesting combination of native longer than seven days.
resources. If designed and installed plants. Rain gardens can also
correctly, rain gardens reduce the eliminate unsightly erosion
amount of runoff from hard, problems on your property by Planning for Your Rain
reducing excess water from
impervious surfaces by up to 98
rooftops or driveways. They can Garden
percent. As this water is no
Choose a location
How rain gardens remove pollutants
Follow these placement
Pollutant Removal Mechanism Pollutants Removed guidelines to help make the rain
Absorption to soil particles Dissolved metals and soluble phosphorus garden more enjoyable for you
Small amounts of nutrients including phosphorus and your neighbors:
and nitrogen
Microbial processes Organics, pathogens Remember that the purpose
Exposure to sunlight and dryness Pathogens of the rain garden is to put
water into the ground! Place
Infiltration of runoff Minor abatement of localized flooding, minor
increase in localized base flow of groundwater, your garden at least ten feet
allowing some nutrients to be removed when
groundwater flows through buffer
Sedimentation and filtration Total suspended solids, floating debris, trash, soil-
bound phosporus, some soil-bound pathogens
Brix, H. "Wastewater treatment in constructed wetlands system design, removal processes, and treatment
performance." In Constructed Wetlands for Water Quality Improvement, ed. G.A. Moshiri, 9–22. Boca Raton, Fl:
CRC Press, 1993. Adapted in W. Hunt and N. White, Designing Rain Gardens. NC State University Cooperative
Extension, 2001. http://www.engr.uga.edu/service/outreach/Stormwater%20BMP/BioretentionOverview.pdf

2. away from your foundation on lakefront, stream front, or unsightly. You may prefer to
in order to avoid water coastal property, contact your carry your water underground
seepage in your basement. local code enforcement officer via plastic or PVC pipe.
before you begin. If you live Grass-lined shallow ditches,
Do not place a rain garden
in Maine’s unorganized or swales, can be used to direct
over a septic tank or leach
territory, contact the Land water to the rain garden. These
field.
Use Regulation Commission ditches should be gently sloped
Do not place a rain garden (LURC) at 207-287-2631. to avoid erosion. The side slopes
near your drinking water well. of the ditch should be no steeper
Determine how big your than a 2:1 ratio (a one-foot rise for
Be aware of and avoid rain garden should be
underground pipes and every two feet across).
utilities. If you don’t know For best water quality If you expect heavy flows of
where they are, call Dig Safe® treatment benefits, the rain garden water (e.g. from a large driveway
at 1-888-DIG-SAFE (344-7233) should hold the water from a area), a rock-lined ditch is
at least three days before one-inch rainstorm. An easy way advisable. Line the ditch with
digging. Outline the proposed to ensure this is to make the rain landscape fabric in order to
area with white paint. Dig garden 30 percent of the drainage prevent it from eroding.
Safe® will automatically notify area. To calculate that volume, Stabilize the area where the
all of its member utilities figure out the size of the rooftop, water enters your rain garden
(gas/oil/steam, electric, driveway, or other impervious with stone to prevent erosion of
communications, water, and surface that will drain into your the rain garden. Watch this area
sewer) that own underground garden in square feet, and make carefully during the first few
facilities in the area of the the garden area 30 percent of that rainstorms following installation.
excavation so that they can area. For example, a 1000-square-
mark their facilities. foot rooftop would require a 300-
square-foot rain garden.
Check for any private wiring
You can make the rain garden I have a lot of standing water
or underground utilities.
larger than 30 percent of the on my property. Can I still have
Look around for lights in the
drainage area, or as small as 20 a rain garden?
yard, such as spotlights on
percent. Simply use 30 percent as Rain gardens are designed to
flagpoles or signs, lights at
a guideline. infiltrate water. Standing water
the end of the driveway, and
indicates poor infiltration, and we
sheds with electricity. Decide how to channel the do not recommend directing
Place the rain garden in a flat water additional water to these naturally
wet areas.
area if possible to make How you direct water from the
installation easier. downspout, driveway, or other
Do not place the rain garden hard surface to the rain garden is
in a naturally wet area. Wet a matter of choice. Some common
spots may seem ideal, but methods include gutter extensions,
they will drain too slowly. piping, and ditches.
Gutter extensions are simply
Avoid trees and tree roots, as
metal gutter pipes attached to the
they may be injured by nearby
ends of your downspouts. They
digging and may not tolerate
must be angled downward
additional moisture in the soil.
slightly for the water to flow. The
Maine has mandatory advantage of gutter extensions is
protective Shoreland Zoning that they are easy to install.
regulations. If you are working However, some people find them
2 UNIVERSITY OF MAINE COOPERATIVE EXTENSION

3. Plan ahead for grass central portion of the garden the lowest portion of the rain
removal must be six inches below the garden, and dry-tolerant plants
grade of the surrounding land in for the edges.
If the rain garden is located in order to temporarily hold water. Use native plants whenever
an existing lawn, you may want Gently slope the garden to this possible. Native plants will
to kill the grass before digging. lowest point to avoid erosion survive better in our environment.
This takes some forethought, as within the garden. A one-inch For help selecting native plants
you will need to lay black plastic drop for every foot across is a that meet your light, moisture,
or a tarp on the lawn until the good rule of thumb. For a 300- and height requirements, consult
grass dies (doing this over the square-foot rain garden, choices our bulletin #2500, Gardening to
winter works best). include a circular garden with a Conserve Maine’s Native Landscape.
Do NOT use a weed killer such 20 foot diameter, or a longer, This bulletin specifies the light
as Roundup® to kill grass. You narrower garden approximately and moisture needs and eventual
can always simply remove the 10 feet by 30 feet. height of native perennials and
sod as you excavate the garden, Remember that rain gardens
and use it elsewhere if possible. on slopes will need to be dug
Estimate your cost more deeply into the high side of
the slope to produce a level Buying your plants
The cost will depend on how bottom. You will need to build a
much work you decide to do berm, or hump, on the lower end Buy plants with healthy root
yourself. If you do all of the work— systems. The healthier the root
to keep the water in the garden.
system, the quicker your plants will
digging the garden, buying the The design stage provides an become established. Use only
plants, planting, and mulching— opportunity to get creative. While nursery-propagated plants or
your costs will range from three to thinking about the shape of the those from your own garden. DO
five dollars a square foot. If you garden as well as the color, shape, NOT collect plants from the wild. If
hire a landscaper to do some or you buy bare-root perennials, be
and height of the plants, consider sure to keep the roots moist until
most of the work, such as design adding elements such as stone or you plant them.
work, excavation, or planting, the fencing, or set a bench nearby.
total cost could approach ten to Personalize your garden! “Plugs” will get you more plants
for less money. These small-
fifteen dollars a square foot.
sized seedlings grown in trays
Select plants for your take longer to fill in the space in
Designing Your Rain design your garden, but plugs can help
keep costs down.
Garden When selecting plants, consider
• zone hardiness, Most reputable nurseries have
selections of native plants. If you
Determine shape and • sunlight needs, are unsure, ask nursery staff! They
placement • moisture needs, are very knowledgeable, and will
• soil type needs, often have other suggestions if a
Once you have calculated the particular plant is not available.
• height and width,
size of your rain garden, determine Also, asking for native plants may
• color,
a general shape, and position the convince nurseries to offer more of
• texture, and them. For sources of native plants,
garden within your landscape.
• whether they are native. consult our bulletin #2502, Native
Have fun, and explore two or
Plants: A 2002 Maine Source List
three options before making a Is your site shady or sunny? (see Resources section).
final design decision. Remember that it takes more than
Rain gardens can be circular, six hours of sunlight to be Plan ahead. Nurseries will have a
larger selection in the spring than
kidney-shaped, or long and considered “full sun.” Choose
at the end of the summer. You
narrow. The shape of the garden plants that will perform well in may have to visit multiple
depends on your wants and the light you have available. nurseries if you want a large
needs. Just remember that a Choose water-loving plants for number of a particular plant.
ADDING A RAIN GARDEN TO YOUR LANDSCAPE, BULLETIN #2702 3

4. shrubs. Plants designated “H” Once you know the size, shape, Cover the berm with grass or
(hydric) will do well in the lowest, and location of the rain garden, mulch to prevent erosion. If you
wettest areas of the rain garden, it’s time to get your hands dirty! seed the berm, use straw to
while “M” (mesic) to “S” (sub- If you do all the work yourself, it prevent it from eroding until the
xeric) will do well in the drier areas. may take the better part of a day. grass takes hold.
Another good resource is The Consider inviting friends to make
Buffer Handbook Plant List, which the work faster and more fun. Plant your rain garden
indicates whether plants will do First, delineate the outline of This is the fun part!
well in wet, moist, or dry the rain garden on the ground. You Set your plants out in the
conditions, and includes native as can use a garden hose, string, or garden to match your design. Now
well as noninvasive, nonnative spray paint. Be flexible. Even the you can adjust the position of the
plants. (See Resources section for most carefully sketched plan may plants, if necessary, before you
both publications.) need to be adjusted to fit the area. start planting. If possible, keep
If you have not already killed the plants in their pots to prevent
Installing Your Rain the grass in your garden area with them from drying out before they
a black plastic or other covering, are planted. Wrap bare-root plants
Garden you will need to remove the sod in wet newspaper until planting.
as you excavate the garden. Do Remember that you don’t want
Avoid wet conditions NOT use a weed killer such as to compact the soil. Work from
Be sure to install your rain Roundup® to kill the grass. one side of the garden to the other
garden when the soil is dry. If you Try not to compact the soil as to reduce the amount of foot traffic
disturb wet soils, you compact you dig the rain garden. Work in the garden. If you think that
the soil to the point that water from one side to the other side, or you have packed the soil down
can no longer infiltrate—which from the center to the outside, so too much, use a rake to loosen it.
will defeat the entire purpose of a you don’t pack down the soil. Dig each hole twice as wide as
rain garden! Loosen the soil at least two the pot and deep enough to keep
feet deep. Even though the garden the crown of the plant level with
Dig your garden will only be six inches deep in the the ground. Make sure your plant
center, loosening the soil will help is level, then fill the hole with soil
Soil mix matters your plants establish root systems and pack the soil around the
The rain garden should allow in this new environment. Now is plant to remove any air pockets.
water to easily seep into the the time to add compost or other Water immediately after
ground. If your soil is mostly clay, soil amendments if needed. planting. Giving the plants a good
you may need to amend the soil Use extra soil to create a berm soaking will give your rain garden
to make it more permeable. A
on the downslope side of the a good start. Use a watering can if
recommended soil mix is 50 to
60 percent sand, using native soil garden. The berm will act as a possible: a high-pressure blast
for the remainder. Adding up to wall to hold water in the garden from a hose will push soil away
20 percent compost in place of during storms. Make the berm from the plant and keep the water
native soil will enhance initial three to six inches high and eight
plant growth, and high-clay soils from soaking in, doing more harm
will need even higher amounts of
to twelve inches wide, with gently than good. Water the new plants
compost, organic matter, or topsoil sloping sides. Taper it off as it before adding mulch to ensure
to increase soil permeability. wraps around to the inlet of the that the maximum amount of
rain garden. Now stomp on it! water reaches the roots.
This soil needs to be compacted
to hold the water in the garden Mulch your garden
before it soaks into the ground.
4 UNIVERSITY OF MAINE COOPERATIVE EXTENSION

5. The value of mulch is often
overlooked. Mulch is important
Maintaining Your Rain maintenance: weeding, pruning,
plant replacement, mulching, and
in any garden to keep plants Garden supplemental watering during
moist and discourage weeds. dry spells.
Layering sheets of newspaper Watch your rain garden the While some people trim dead
around the plants before adding first time it rains. Where does the stems and leaves from their
mulch will provide an added water go? Does it pond where perennials before winter, you can
weed barrier. you intended it to? Or are the leave them over the winter to
Apply a three- to four- inch moisture-loving plants left high provide food for birds and wildlife.
layer of mulch to your rain garden. and dry? Does the force of the Once new growth appears in the
Be sure to keep the mulch away water erode the mulch and soil at spring, remove the dead stems
from the crown of each plant. the entrance to the rain garden? and leaves.
Add some additional mulch each Use the first few storms to evaluate
year for a few years, until the your garden. If the contours need Solving plant problems
plants have matured, so the soil to be adjusted, use a rake or
Here are some considerations
does not dry out too quickly. shovel as needed. Strategically
if your rain garden plants fail to
After a few years, mulch is not placed rocks can slow the force of
thrive:
necessary, unless you prefer its the water.
more formal appearance. If you have used shallow New plants need a consistent
How much mulch will you ditches or swales to direct water supply of water until their
need? A cubic yard1 of mulch will to the rain garden, inspect these roots are established—even
cover a 100-square-foot area with ditches often to be sure that the though your rain garden
about three inches of mulch. bottoms are not eroding. Keeping catches stormwater. Your rain
With the exception of bark the side slopes of the ditches no garden will need one to two
chips and artificially colored steeper than 2:1 (for every two inches of water per week
mulches, you can generally use feet across, a one-foot rise) will during the first year.
any type of mulch that will stay help prevent erosion. Consider the location of each
in place and retain moisture. Bark Keep in mind that during the plant within the garden.
chips don’t work because they first year, especially during the Some plants will not tolerate
tend to float away in rain gardens, dry summer months, you may having their roots dry out,
and artificially colored mulch will need to water the rain garden so while others do not like them
leach color into the soil. We have that the plants can get established. to be moist all the time.
used Superhumus and Erosion Use a rain gauge to keep track of
the rainfall. Your rain garden will Double-check the hardiness
Control Mix—blended products
need one to two inches of water zone rating of your plants. If
from earthlife™—in our test rain
per week the first year. you end up replacing plants,
gardens with success. If you are
Frequent weeding will be choose plants rated for a
unsure, ask your nursery
necessary in the first few years colder zone than yours, to
professional.
before plants become established. ensure that they can survive
Nurseries sell mulch by the
In order to distinguish between the very coldest temperatures
bag and by the cubic yard. If you
weeds and young plants, consider they might experience.
don’t have access to a truck, most
nurseries will deliver for a adding plant labels next to each Make sure that you have
nominal fee. plant. used plants well suited to the
Once the plants mature and light levels and light duration
become established, maintenance of your garden’s location.
of a rain garden is nothing more
than routine landscape
1
27 cubic feet, or about what will fit in
the back of a pickup truck
ADDING A RAIN GARDEN TO YOUR LANDSCAPE, BULLETIN #2702 5

6. Example of a Sunny Rain Garden Design Plant List for a Sunny
Rain Garden
Plants for the wetter center of the
garden:
Woody shrubs:*
SS: Clethra alnifolia, summersweet. 5–6’H x
4–6’W. Late-to-emerge foliage. Fragrant,
large, white flower stalks in summer.
Perennials:**
CA: Lobelia cardinalis, cardinal flower. 2–4’H
x 1’W. Bright red flowers from July to
September.
T: Asclepias tuberose, orange butterfly
weed. 2–3’H x 2–3’W. Can handle dry
areas. Orange blooms from June to
September.
I: Iris versicolor, blue flag iris. 2–4’H x
2–4’W. Blue flowers in spring.
M: Caltha palustris, marsh marigold. 8”H x
1’W. Glossy heart-shaped leaves with
bright yellow flowers in the spring.
J: Eupatorium maculatum, joe-pye weed.
3–5’H x 1–2’W. Red stems, purple-red
flowers from July to September.
SM: Asclepias incarnate, swamp milkweed.
2–3’H x 2–3’W. Will not tolerate drought.
Showy, flat, reddish flowers from July to
October.
Plants for the dryer outer edge of
the garden:
Woody shrubs:*
P: Potentilla arguta, tall cinquefoil. 1–3’H x
1–3’W. Thick leaves and many white
flowers all summer.
Perennials:**
G: Geranium maculatum, wild geranium.
1–2’H x 2’W or more. Purple flowers in
the late spring and sometimes again in
the fall. Pretty foliage.
A: Anemone canadensis, windflower. 2’H x
10”W. Pure white blossoms in June.
Large, attractive leaves.
LO: Lobelia spicata, spiked lobelia. 3–5’H x
3–5’W. Blue flowers from June to
August.
FA: Symphyotrichum umbellatus, flat-topped
aster. 3–7’H x 3–7’W. White to
yellowish-centered flowers in the fall.
AS: Symphyotrichum novae-angliae, New
England aster. 3–7’H x 3–7’W. Purple
flowers in the fall.
H: Helenium autumnale, perennial
sunflower, 3–5’H x 2–3’W. Lots of yellow
flowers in the fall.
*Woody shrubs: Though they may shed
their leaves, the woody structure of these
plants will provide winter interest in the
garden.
**Perennials: These plants die over the
winter and sprout new shoots in the spring.
Sometimes some of last year’s foliage will
survive the winter, but generally you should
trim off the dead foliage in late fall and wait
for the green growth of spring.
6 UNIVERSITY OF MAINE COOPERATIVE EXTENSION

7. Plant List for a Shady Example of a Shady Rain Garden Design
Rain Garden
Plants for the wetter, shadier
center of the garden:
Woody shrubs:*
HV: Hamamelis vernalis, vernal witch hazel.
6–10’H x 6–10’W. Showy golden yellow
fall color. Long-lasting, scented yellow
flowers in the late winter.
RH: Rhododendron canadense, rhodora
(native rhododendron). 1–3’H x 1–3’W.
Showy purple flowers in the spring.
Tolerates wet, acidic soil.
LE: Ledum groenlandicum, Labrador tea.
1–3’H x 1–3’W. Showy white flowers in
late spring, tolerates wet feet.
IV: Ilex verticillata, winterberry. 6–8’H x
6–8’W. Plant a male and female to take
advantage of showy orange berries that
persist all winter long.
Perennials:**
RF: Osmunda regalis, royal fern. 2–5’H x
2–5’W. Large, showy fern. Needs
moisture! You must keep this plant
watered if you are experiencing low
rainfall.
C: Aquilegia canadensis, native colombine.
1–2’H x 1–2’W. Showy red and yellow
flowers in spring. Sometimes blooms
again in autumn. Beautiful foliage.
S: Onoclea sensibilis, sensitive fern. 2'H x
18”W. Soft, green fern. Thrives in moist
areas.
CA: Lobelia cardinalis, cardinal flower. 2–4’H
x 1’W. Bright red flowers from July to
September.
Plants for the dryer outer edge of
the garden:
Woody shrubs:*
W: Comptonia peregrina, sweetfern. 2–4’H
x 2–4’W. Rickrack-shaped leaves are
heavily scented when crushed. Comptonia
should be purchased in sod form as it is
difficult to establish individual plants.
Tolerates sandy, dry, rocky soil.
AR: Arctostaphylos uva-ursi, bearberry.
6–12”H x 1-2W. Shiny evergreen leaves
turn bronze in the fall. Small white to pink
flowers in the early spring, bright red
berries in late summer that persist through
winter. Tolerates sandy, dry, rocky soil.
PHOTO: EDWIN REMSBERG, USDA-CSREES
Perennials:**
G: Geranium maculatum, wild geranium.
1–2’H x 2’W or more. Purple flowers in
the late spring and sometimes again in
the fall. Pretty foliage.
*Woody shrubs: Though they may shed
their leaves, the woody structure of the plant
will provide winter interest in the garden.
**Perennials: These plants die over the
winter and sprout new shoots in the spring.
Sometimes some of last year’s foliage will
survive the winter, but generally you should
trim off the dead foliage in late fall and wait
for the green growth of spring.
ADDING A RAIN GARDEN TO YOUR LANDSCAPE, BULLETIN #2702 7

8. Resources
Native plant lists from the Portland Water District and the Maine Developed by UMaine Extension
Department of Environmental Protection: part of the Conservation Assistant Scientist Laura Wilson
Practices for Homeowners fact sheet series. Available at and Water Resource Specialist
http://www.pwd.org/news/publications.php. Mary Gilbertson of the Portland
Native Plant List; Part/Full Shade, Dry Soil, DEPLW0777, May Water District, with landscape
2006. diagrams by Kirsten Reberg-Horton.
Native Plant List; Part/Full Sun, Dry Soil, DEPLW0778, May 2006. Editor: Kyle McCaskill
Native Plant List; Part/Full Shade, Moist to Wet Soils, DEPLW0776,
Design: Cindy Eves-Thomas
May 2006.
Native Plant List; Part/Full Sun, Moist to Wet Soils, DEPLW0779,
May 2006. www.umext.maine.edu
Landscapes for Maine bulletins from UMaine Cooperative Extension.
A Member of the University of Maine System
Available at www.umext.maine.edu or by calling 800-287-0274
Published and distributed in furtherance of Acts of
(in Maine): Congress of May 8 and June 30, 1914, by the
University of Maine Cooperative Extension, the Land
Designing Your Landscape for Maine, bulletin #2701 (Orono, ME: Grant University of the state of Maine and the U.S.
Department of Agriculture cooperating. Cooperative
2005). Extension and other agencies of the U.S.D.A.
Gardening to Conserve Maine’s Native Landscape: Plants to Use and provide equal opportunities in programs and
employment. 11/06
Plants to Avoid, bulletin #2500 (Orono, ME: 2003).
Produced by the UMaine Cooperative
Native Plants: A 2002 Maine Source List, bulletin #2502 (Orono, Extension Communications Office.
ME: 2002).
The Buffer Handbook Plant List, Cynthia Kuhns for the Maine
This material is based upon
Department of Environmental Protection. DEPLW0094-A2001, work supported by the
1998, Revised 2001. Available at http://www.maine.gov/dep/ Cooperative State Research,
blwq/docwatershed/bufhand.htm. Education, and Extension
Service, U.S. Department of
Need an expert? Agriculture, under agreement
nos. 2003-51130-02074 and
In Central or Northern Maine: 2004-51130-03108, through the CSREES
Laura Wilson, Extension Assistant Scientist New England Regional Water Quality
University of Maine Cooperative Extension Program.
495 College Avenue
Orono, ME 04473-1294
207-581-2971 or lwilson@umext.maine.edu
In Southern Maine:
Mary Gilbertson, Water Resource Specialist
Portland Water District
1 White Rock Road
Standish, ME 04084
207-774-5961 x3336 or mgilbertson@pwd.org
References
Bannerman, R., E. Considine, and J. Horwatich. Rain Gardens: A How-
To Manual for Homeowners. UWEX Publications GWQ037.
University of Wisconsin-Extension, 2003.
Dietz, M. E. and J. C. Clausen. “A Field Evaluation of Rain Garden
Flow and Pollutant Treatment.” Water, Air, and Soil Pollution 167
(October 2005): 123–128.
Wilson, G. “Burnsville Rainwater Gardens.” Land and Water 48, no. 5
8 UNIVERSITY OF MAINE COOPERATIVE EXTENSION