Rainy Day Gardens

1. Rainy-Day Gardens
Imaginative plantings that help capture and clean runoff are attracting the attention of home
gardeners, landscape designers, and watershed managers. BY MARYALICE KOEHNE
A
N I D E A W H O S E time has If you haven’t heard of a rain garden National interest in storm water man-
come, rain gardens are storming before, the basic concept is quite sim- agement has been increasing exponen-
the country, showing up in pri- ple—they are designed gardens or tially because of the growing concern
vate gardens, arboretums, housing devel- plantings that help capture and clean about non-point source (NPS) pollution,
opments, parking lots, and along storm water runoff from gutters, drive- which the U.S. Environmental Protec-
roadways from the Chesapeake Bay to ways, lawns, and other impermeable or tion Agency (EPA) now considers the
Puget Sound. In Seattle, they’re part of a semi-permeable surfaces. This helps leading cause of water quality problems
DO NNA KRISCHAN
“Salmon Friendly Gardening” program, prevent soil erosion and reduces the
while in Maryland they are being pro- amount of pollutants entering our rivers Above: Lorrie Otto used only native plants to
moted as a way to “Save the Bay.” and ground water. create this rain garden in Bayside, Wisconsin.
March / April 2 0 0 3 37

2. The middle planting zone of the garden is suit-
A TYPICAL RAIN GARDEN able for plants that prefer consistently moist
soil but tolerate periods of drought. Examples:
sweetbay magnolia (Magnolia virginiana), river
birch (Betula nigra), swamp azalea (Rhodo-
The lowest zone of the garden is dendron viscosum), cardinal flower (Lobelia
ideal for plants that like wet feet cardinalis), switch grass (Panicum virgatum),
most of the time but can with- black-eyed Susan (Rudbeckia hirta).
stand occasional dry spells. Ex-
The outermost, driest amples: New England aster
edge of the garden can (Aster novae-angliae), sedges
be planted with any (Carex spp.), marsh marigold
trees, shrubs, and (Caltha palustris), swamp milk-
herbaceous perennials weed (Asclepias incarnata).
suited to your region
and site.
Small stones or pebbles at
Rainwater is directed away
the terminus of the pipe
from the house to a naturally
create a free-draining area
low spot in the yard by means A layer of mulch over the
for excess water to collect
of a gutter extension pipe, rain garden reduces weeds
initially before seeping into
shown here, or French drains. The saucerlike depression of the rain garden, which should and helps filter runoff.
the garden itself.
be fairly shallow and no more than a foot or so deep in the
center, is filled with a mixture of soil, organic matter,
sand, and gravel to permit good drainage.
in the United States. Unlike pollution tion ponds, low impact developments cause over time they have developed a
that can be traced directly to one (LIDS), infiltration basins, stormwater spongy litter layer that absorbs water and
source—such as an industrial plant or a marshes, and even “wet gardens.” allows it to slowly percolate into the soil,
sewage treatment facility—NPS pollu- Consultants to the Prince George’s where it replenishes watersheds and
tion is caused by a variety of manmade County, Maryland, Department of Envi- aquifers. According to the EPA, national
and natural pollutants that are picked up ronmental Resources (DER) are credited forests alone are responsible for capturing
by runoff and then deposited into water with coining the term “rain gardens,” and filtering the drinking water used by
bodies and water sheds. These pollutants which helps convey the idea of relatively more than 60 million Americans.
include fertilizers, pesticides, oil, grease, small, colorfully planted areas that collect “It’s not so much that this is a new
de-icing salts, heavy metals, bacteria rain water or snow melt. In home gardens, idea,” says Carole Barth, an environmen-
from animal wastes, and even sediment. they are typically located near the down- tal planner with the Prince George’s
EPA studies indicate that as much as spouts of gutters, or in areas where water County DER, “but we’re putting back
half of all pollutants in stormwater come tends to wash off a sloping driveway. The water in the environment like Mother Na-
from home landscapes, and some com- water routed to these areas is filtered nat- ture did before we messed it up.”
munities are now requiring home and urally by the garden’s plants and soils. As Using the catchy slogan “From Rain-
business owners to find ways to avoid an added bonus, these plantings attract bows to Rain Gardens,” the DER’s goal is
discharging stormwater into sewers. If and provide habitat for birds, butterflies, to foster a million rain gardens to help
you consider that a city block generates and other beneficial wildlife. protect the Chesapeake Bay through an
nine times more runoff than a woodland outreach program that extends to Master
area the same size, it makes even more TAKING A CUE FROM NATURE Gardeners, garden clubs, local watershed
sense to plant rain gardens. As with many successful ideas, the eco- groups, and schools.
Rain gardens have been part of new logical model for rain gardens comes from In other words, rather than continuing
housing developments and road construc- nature, where vegetation, soil, and soil or- to treat rainwater like a waste product by
tion projects for more than 20 years, but ganisms slow down, filter, and store rain- funneling it into stormwater sewer sys-
MARK MILLER
they have often been saddled with clunky water. Mature forests are particularly tems, it’s being valued as the precious nat-
and unromantic names such as bioreten- critical components of this process be- ural resource that it is.
38 the American Gardener

3. FINDING A SITE where you live. But even a relatively small mulch to facilitate drainage. A slightly
Late winter to early spring, when snows rain garden can help alleviate runoff prob- acidic soil—with a pH of 5.5 to 6.5—has
melt and rains fall, is the perfect time to lems. Consider starting with just one small been found to be ideal for the type of bio-
evaluate your property to see if you can plot that can easily be dug by hand, then chemical reactions that remove pollutants.
benefit from creating one or more rain extend it or add others later. If you have a Some rain gardens include an underdrain
gardens. Look for a low point in your steeply sloping lot or get a high volume of system or an overflow outlet to handle ex-
yard where water tends to pool after water flow during major storms, you may cess water during heavy storms.
storms, or an area along the street or want to consult a landscape architect. The key is that the central basin
driveway where you get a washout every Rain gardens should always be set well shouldn’t be so deep that water will stand
time it rains. If you have had to add ex- away from buildings, so there’s no chance in it long enough to kill plants or allow
tenders to your gutters or install a French excess water could flow into the basement. mosquitoes to breed in summer. If water
drain to route water away from the What rain gardens usually have in overflows the depression during a heavy
house, you may have perfect conditions common is a relatively shallow saucer- or storm, it should be absorbed by plantings
for a rain garden. bowl-shaped depression where runoff ini- around the perimeter.
There is no single formula for creating tially collects. The soil in the bottom of Before planting your rain garden, ex-
rain gardens—their shape, size, and plant- this depression is often amended with a perts advise that you watch how the site
ings depend on many factors, including blend of organic matter, sand, gravel and handles two or three rainfalls. This will
SOLVING PROBLEMS AT HOMES AND SCHOOLS
Rain gardens at three very different sites in and around Milwaukee, Wisconsin, illustrate how diverse such gardens can be
and how they can be used both to solve drainage problems and to create beautiful, interesting plantings.
When Katie and John Clark were looking for something to replace the scraggly, balding lawn that underlay their wooded front
yard, the idea of a meandering dry river bed seemed like a practical solution. But once runoff water began tumbling over small
waterfalls in their new installation and woodland plants began to thrive, they realized that besides solving aesthetic problems,
this new installation at their home in Elm Grove, a suburb of Mil-
waukee, boasted many advantages. During storms, when rainwa-
ter gushes down the driveway from the cul-de-sac that fronts their
house, it now courses through the channel to a wooded area be-
hind their house. As the runoff from their property and the street
pools there, it soon infiltrates the soil and helps recharge and re-
new the groundwater.
At Indian Hill School in Brown Deer, a northeastern suburb,
students routinely use a rain garden—as well as prairie and
woodland plantings—as part of science lessons and projects.
Begun in 1990, this verdant paradise fronting the modern, flat-
roofed building was destined to become a formal garden before
several mothers and local environmental activist Lorrie Otto lob-
bied the school board to install more naturalistic plantings. Wa-
ter that flows through the rain garden eventually drains into a
pond that hosts frogs, dragonflies, and other wildlife. “This is
our outdoor classroom,” said principal Rebecca Bell. “Each A rain garden at Indian Hill School in Brown Deer, a suburb of
teacher uses it differently and ties it into the curriculum.” Milwaukee, Wisconsin, filters water that eventually drains into
Otto has solved runoff problems in her own garden with what this pond. The rain garden and pond are integral parts of the
she calls “a drainage ditch that goes nowhere.” This early ver- school’s outdoor classroom activities and science projects.
sion of a rain garden she created in the grass-clad drainage
ditch that ran alongside the street in the front of her yard initially drew the ire of city officials. The city soon let her have her
own way, however, and now stands of mature native plants such as white turtlehead (Chelone glabra), Indian grass (Sorghas-
trum nutans), and Joe Pye weed (Eupatorium fistulosum) edge a pond that collects filtered street runoff.
A lifelong environmental activist, this feisty 83-year-old is one of the founding members of Wild Ones—an organization
that advocates naturalistic gardening—and is credited with fostering passage of legislation banning use of the pesticide DDT
in Wisconsin in 1970, two years before Congress outlawed the pesticide nationally.
“I think there should be ordinances saying you must keep the rain water that falls on your property right there,” says Ot-
DO NNA KRISCHAN
to. On this issue, at least, city officials around the country are finally beginning to see eye to eye with her. —M.K.
March / April 2 0 0 3 39

4. allow time for the amended soil in the
basin to settle—if it settles too much, you
may need to add more soil—and will let
you see how long water stands in the
basin. If you still have standing water after
three days, you may need to improve the
drainage.
Plants should be selected to fit the site
chosen for the rain garden. Determining
the exposure of the location—degree of
sun or shade—is particularly important.
Rain gardens generally have two or
three planting zones. The innermost
planting zone in the bottom of the central
basin should include plants that are happy
having “wet feet” most of the year but that
will also tolerate periods of drought—
plants native to wetlands are good choic-
es here. The second planting zone, on the
sloping walls of the central basin, should
include plants that tolerate periodic im-
mersion and are also drought tolerant—
plants native to the edges of streambanks
are appropriate here. The third planting
zone, around the perimeter of the basin,
can include a variety of herbaceous peren-
nials, shrubs, and even trees suited to your
regional soil and climate.
Experts advise that all planting areas in
rain gardens be covered with two or three
inches of organic mulch. Research has
shown that in addition to reducing weed
problems, the mulch helps remove pollu-
tants from the water filtering through it.
As the concept of rain gardens spreads
rapidly, plant lists suited for different areas In Seattle, severe runoff problems in one neighborhood were solved by creating rain gardens
of the country are becoming available along the length of an entire street. Top: Before construction of rain gardens, runoff from this street
through regional university Extension flowed into a local creek. Above: Rain gardens not only absorb runoff but look great.
agencies, departments of environmental
protection, and some specialty nurseries individual property owners in a three-and- The prototype project has proven so
(see “Resources,” page 41). a-half block area along a busy street in a successful that this technique is being ap-
Usually, a minimal financial invest- 1950s subdivision that was built without plied to other streets that are subject to se-
ment can yield an attractive addition to curbs or gutters (see photographs above). vere stormwater runoff.
your landscaping. Previously, ditches along the edges of Another innovative urban rain garden
the properties carried a high volume of project is on display in the Swede Hollow
REDUCING SUBURBAN RUNOFF water that was contributing to the over- neighborhood of St. Paul, Minnesota,
ERIK STUHAUG/COURTESY OF THE CITY OF SEATTLE (2)
Existing neighborhoods of major cities are load of Pipers Creek, a nearby waterway. where the neighborhood association joined
also benefiting from rain gardens that slow Now, the flow is stemmed by a series of forces with the city to help protect a re-
the rush of storm water into municipal re- carefully designed plantings that run the stored wetland area along the Mississippi
tention ponds and sewage facilities. For ex- length of the road. Each homeowner was River from polluted runoff. Two vegetated
ample, Seattle, Washington, claims that able to chose from among six varieties of swales funnel stormwater from a street in-
the innovative Street Edge Alternative deciduous trees, five evergreens, 20 shrubs, to the 900-square-foot Maria Bates Rain
(SEA Street), completed in 2000 by the 10 herbaceous perennials, two low-grow- Garden, designed by Barr Engineering.
Seattle Public Utilities and the Seattle De- ing ground covers, and six types of wet- Local elementary school students plant-
partment of Transportation, is the first of land plants. While city workers did the ed the garden, which features a diverse
its kind in the country. The project in- planting, property owners are responsible blend of native and adapted exotic plants
volved city agencies working directly with for maintaining the gardens. such as big bluestem (Schizachryium sco-
40 the American Gardener

5. parium), New England aster (Aster novae- pay homeowners $50 per disconnected
angliae), blazing star (Liatris aspera), black- downspout beginning in 2004. By 2007,
eyed Susan (Rudbeckia fulgida ‘Goldsturm’, disconnections will be mandated. Besides Resources
and feather reed grass (Calamagrostis ✕acu- rain gardens, green roofs, rain barrels, roof Environmental Protection Agency,
tiflora ‘Karl Forster’). Neighborhood artists restrictors, and increasing the tree canopy www.epa.gov/cgi-bin/epa
added a meandering walkway with signage are options the district intends to pursue.
that helps explain the garden’s function, Friends of Bassett Creek (a private con-
and benches encourage passersby to stop RESTORING PARADISE TO PARKING LOTS servation group in Minneapolis, Min-
and savor the colorful plantings. Designing rain gardens in association nesota), www.mninter.net/~stack/rain/
with parking lots—which
are major sources of both GreenSpace Partners (a community
pollution and runoff—is group in Minneapolis, Minnesota),
something many municipal- www.greeninstitute.org/GSP
ities, botanical gardens, and
businesses are exploring. National Wildlife Federation’s Back-
“We’ve installed a demon- yard Wildlife Habitat Program,
stration rain garden that www.nwf.orgbackyardwildlifehabitats
catches runoff from the
parking lot at the new Alter- Natural Resources Defense Council,
ra Coffee House/Milwaukee www.nrdc.org/water/pollution/
Flushing Station on the grunoff.asp
lakefront,” says Kevin
Shafer, executive director of Prince George’s County, Maryland, De-
MMSD. partment of Environmental Resources,
Botanical gardens and ar- (301) 883-5852 / (301) 883-5834
boretums see rain gardens as www.co.pg.md.us/pgcounty/govern
important elements of edu- ment/agencyindex/der/ppd/lid/bio
cational and environmental retention2.asp
programs. In cooperation s Offers booklet, new bioretention
with the Virginia Depart- plant list of 150 hardy plant species.
ment of Forestry, the Blandy
Experimental Farm near Seattle SEA Streets project,
Boyce, Virginia, installed a www.ci.seattle.wa.us/util/SEAstreet
rain garden at its visitor’s s/default.htm
parking lot in 2001. And a
Above and top: At the Maria Bates Rain Garden in St. Paul, rain garden is planned as University of Wisconsin Extension
Minnesota, students from a local elementary school planted part of new parking areas Service, Madison WI. (608) 262-
the garden with a mixture of native and adapted exotic plants. being constructed during 3346 or toll-free (877) 947-7827.
renovation of the visitor cen- http://clean-water.uwex.edu/pubs/
The Seattle and St. Paul rain gardens are ter at the Minnesota Landscape Arbore- s Offers publication titled Rain Gar-
voluntary efforts to reduce stormwater tum in Chanhassen. dens: A Household Way to Improve
runoff, but some municipalities are mov- As we look for ways to reconnect our Water Quality in Your Community.
ing toward mandatory programs. gardens with the natural world around us,
In Milwaukee, a new law will require it’s important to keep in mind that no gar- Virginia Department of Forestry,
45,000 homeowners and businesses to dis- dens are truly natural. Wherever human http://state.vipnet.org/dof/rfb/
connect downspouts from sanitary sewers settlement disrupts nature, problems de- riparian/rain_gardens.htm
COURTESY OF CORRIE ZOLL/GREENSPACE PARTNERS (2)
served by the Milwaukee Metropolitan velop unless people remember the words
Sewerage District (MMSD) by 2007. An of conservationist Aldo Leopold: “The Wild Ones, www.for-wild.org
estimated 200 million gallons of rainwater privilege of possessing the earth entails the
that falls during heavy storms will thus be responsibility of passing it on the better for Wisconsin Department of Natural Re-
directed back to the ground, which should our use.” Rain gardens are one way to re- sources, Madison, WI. (608) 264-
eliminate the city’s need to dump diluted duce our own environmental footprint 6217. www.dnr.state.wi.us/
sewage into creeks, the Milwaukee River, while at the same time creating a beauti- s Offers pamphlet titled “Rain Gar-
or Lake Michigan every time three to five ful addition to our landscapes. dens…Nature’s Way to Control
inches of rain falls quickly. Runoff Pollution.”
The district hopes to disconnect down- Maryalice Koehne is a free-lance writer who
spouts from 10,000 homes a year and will lives and gardens in Wauwatosa, Wisconsin.
March / April 2 0 0 3 41