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Native species fare best in bioswales and
need to tolerate frequent downpours
and dry stretches alike.
“Plants should match the hydrology pro-
duced by your region’s weather patterns,”
says Slovensky. “Avoid turf grass, which
has a shallow root system, as well as high
maintenance plants that need fertilization.”
Bioswales should also feature a
matrix of grasses that replicate the plant
density and variety found in naturalistic
settings, Slovensky stresses. Diverse
plants are less vulnerable to disease and
pests. They also don’t need to be fertil-
ized because the rainwater delivers a
constant supply of nutrients, she adds.
Newly created bioswales need an
irrigation component so plants have time
and nutrients to become established,
Grover notes. Depending on your climate
zone, a permanent irrigation system may
be required to support plants during
drought periods.
Bioswales are often placed next to
impervious surfaces, such as parking lots
or large patios, where a barrier is needed
to slow the path of water. Costs are
dependent on the size of the bioswale
and whether earth movers are needed
to break through compact or rocky soils.
This can average $58 per linear foot or
$20-30 per square foot, according to
the Challenge for Sustainability, a private
sector initiative in Boston.
Tend to Maintenance
Manage bioswales like any other land-
scaping. Otherwise they will grow into
an unsightly patch of weeds that does
little to intercept stormwater.
“Because you are incubating a wet-
NR
E
L
/D
O
E
RAIN GARDENS ARE NOT THE SAME AS BIOSWALES, but you can use them
in conjunction with one another like NREL does at its Golden, CO, campus.
Its network of bioswales and rain gardens helped the agency receive SITES
certification.
land-like environment, bioswales require
upkeep,” notes Slovensky. “For example,
you may need to reseed bald spots
where grasses didn’t survive or remove
noxious plants by hand. You should also
monitor for erosion. If the water is pond-
ing, there’s a problem with the slope.”
Native plants can face competition
from invasive species, says Grover. In
Oregon, for example, blackberries are a
noxious weed that flourishes in riparian
areas, which bioswales simulate. It is
best to monitor for weeds before they
choke out native vegetation.
Overgrown bioswales are not only
an eyesore, but their ability to handle
rain events is severely compromised.
Even properly maintained bioswales will
experience sediment buildup over time.
Particularly if they have been in use for
10-15 years, older bioswales may need
to be dredged with an excavator and
replanted, says Grover.
Keep in mind that your city may have
“out of compliance” fines, he adds. Some
inspectors are proactive about flagging
unkempt bioswales, although most will
only take a peek if you have applied for
a building permit. But the risk of having
to completely renovate a bioswale can
be avoided with routine maintenance.
“Integrate the bioswale into a prominent portion of your landscape, such as
in the middle of a parking lot,” recommends Grover. “If it’s in a noticeable
location, it will stay functional because
you want it to look good.” B
Jennie Morton is a contributing editor for
BUILDINGS.
