Backyard
Wetlands
In Your Backyard
A
mini-wetland in your yard can provide
many of the same benefits that natural
wetlands offer. A mini-wetland can replace
the important natural functions of wetlands
that may have been lost when your community
was developed.
A
wetland in your backyard will temporarily
store, filter, and clean runoff water
from your roof and lawn. It will provide
habitat for many interesting creatures--from
butterflies and bees to salamanders,
toads, frogs, and birds.
Most
wetland plants do not require standing
water to grow successfully, and will
survive even in an area that appears
dry during most of the growing season.
If
you have a naturally occurring wet spot
in your yard, or a low swale or drainageway
with heavy clay soils, you easily can
turn it into a wetland paradise. Even
if you do not have a naturally wet spot,
you can establish an area in your yard
to grow many of the beautiful plants
associated with wetlands.
What
is a Wetland?
A
wetland is simply any area where water
covers the soil or keeps it saturated
for at least two or three weeks during
the growing season. You will usually
find them anywhere water accumulates
at a rate faster than it drains away.
Some are inundated year-round while
others only hold water for brief periods
in the spring. Most wetlands are covered
with water for less than a month during
the summer. Wetlands dominated by grasses,
cattails, and similar herbaceous vegetation
are referred to as marshes, while wooded
wetlands, dominated by shrubs and trees,
are called swamps.
The
saturation of the soil limits the types
of plants you can grow to those with
"wet feet." How long the soil
is saturated determines which wetland
plants will grow best. There are many
small wetland plants that grow quickly
when the soil is wet in the spring and
disappear when the soil dries up. Species
like cattails, bulrushes, jewelweed,
and the attractive cardinal flower do
well where there are alternating wet
and dry periods. These plants will survive
persistent flooding as long as most
of the leaves are out of the water.
Water lilies and pond weeds grow well
in permanently flooded ponds.
In
your backyard, toads and tree frogs
(spring peepers) will lay eggs and the
pollywogs will mature where water only
lasts 3 or 4 weeks; other frogs need
longer periods. Where you have permanent
water, the bullfrog pollywogs and small
fish eliminate reproduction of most
other frogs, toads, and salamanders.
Mosquitoes will not survive in wetlands
that dry out in less than a week after
a summer rain or in wetlands connected
to a deeper pond that supports small
fish and large aquatic insects that
feast on them.
Where
to Put a Wetland
A
natural depression or ditch that tends
to stay wet is an ideal place to develop
a wetland. Other areas with heavy clay
soils that drain slowly may also be
suitable. Better drained sites may require
use of a plastic or other type of liner.
Of course, if you are building a backyard
pond, as discussed in another tip sheet
in this series, a shallow area of saturated
soil can be incorporated in the design.
When selecting a site, consider:
Is
the site away from your foundation,
out buildings, existing landscaping
that you want to maintain, or neighboring
properties that might be damaged by
excessive moisture?
Would there be a safety concern for
neighborhood children?
How will the site be integrated into
your plan for maintenance?
If you need supplemental water, is it
readily available or can you use roof
drainage?
If there is an existing wetland, check
state and local wetland regulations
before altering it.
Unless you completely own a ditch, check
with local authorities before making
any alterations. Be sure you won't cause
adjacent properties to flood.
Building a Wetland
Since
wetlands refer to a variety of conditions,
there is a lot of potential for including
wetland plants in your yard. You may
want a wetland that only stays wet for
a short period after heavy rains or
one that stays wet most of the time.
It depends on the site and your desires.
Establishing a wetland in your yard
may be as simple as planting wetland
plants in an existing wet area, or it
may require the same effort needed to
install a backyard pond.
Building
a Wetland in an Existing Wet Area or
Rainageway
In
some instances, all you need to do is
stop mowing during dry periods. Too
often homeowners go to great lengths
to establish plants that are not adapted
to the site or to modify the site, when
it would be more effective to use plants
suited to the conditions. Numerous landscape
plants are well adapted to wet conditions
and will provide beauty as well as wildlife
habitat. Be sure to check the growth
and rooting characteristics of trees
you want to plant. Many wet soil tolerant
trees have shallow root systems or brittle
branches and must be planted a safe
distance from buildings.
Partially
blocking a drainageway or small ditch
to create your wetland by trapping storm
water needs more planning. Where a low
berm less than a foot high will create
a small wetland, planning is not complicated
if:
The
drainage area above the berm is small,
generally less than an acre
There is adequate area for flood flows
to go around and over the berm
The soil contains a high percentage
of clay.
For sites requiring a higher berm, and
those with a larger watershed, you need
engineering advice. For sites with sandy
soil or a lot of rocks, you also may
need to install a plastic liner (described
in the next section) under all or the
lower portion of your wetland.
To
construct the wetland with a small berm
to hold back water for a few days or
weeks:
Put
a stake in the center of the lowest
portion of the drainageway where you
want the berm.
Using a level on a large board or string,
place a stake where a level line reaches
the ground on either side.
Using the same type of level, mark how
far back water will be impounded at
the top of the berm.
Remove any existing sod from an area
about 4 feet wide along the line of
the berm and over about half the area
that will be flooded.
Dig a trench about 1 foot deep along
the center line of the berm and fill
it with slightly damp heavy soil, packed
down firmly.
Build your berm about 4 feet wide at
the bottom and 1 foot at the top. The
center should be 4 to 6 inches higher
than the ends to allow for settling
and to force water flowing over it around
the ends, reducing the likelihood of
erosion.
Cover the compacted berm with purchased
grass sod or the sod you originally
removed from the area.
Plant wetland adapted plants in bands
from the deepest areas to an area about
six inches above the expected high water
level, selected according to the degree
of soil saturation they require.
Building a Separate Wetland
You
can create a wetland in any level area
and make it suitable for most wetland
plants by digging out a depression,
lining it with plastic, refilling it
with soil, and adding water. After selecting
the site, you should:
Using
a hose or rope, lay out the shape of
your wetland. An irregular shape will
appear the most natural. Sometimes a
long narrow curving wetland will fit
nicely into a landscape plan.
Excavate an area 1-1/2 to 2 feet deep.
The sides should slope gently to the
deepest area.
Put an inch of fine sand or lose soil
in the bottom to prevent the plastic
liner from being punctured by small
stones.
Line the depression with sheet plastic.
Hold in place with heavy objects such
as round stones. Or, install a pre-formed
pool liner or use a child's wading pool.
If you live in a region with heavy annual
rainfall, puncture the liner in several
places with pencil-sized holes about
halfway up the sides to allow slow drainage
so the soil will not stay completely
waterlogged for long periods.
If you plan to grow common species of
low maintenance plants adapted to moist
soils in your area, fill the depression
with a mixture of soil and peat. A significant
amount of peat will help retain moisture
and allow for aeration.
If you intend to grow true bog plants
that require acidic soils saturated
with water most of the year, fill the
area with a mixture of half peat and
half humus. Also, you should fill the
lower half of the depression with pea
gravel or coarse sand to assure more
even distribution of water. Burying
a perforated pipe in the pea gravel
connected to an upright pipe fitted
with a hose connection will help add
water evenly to the bog.
Cover the edges of the plastic with
soil to hide them and hold the liner
in place.
Building a Wetland by a Backyard Pond
Putting
a shallow wetland at one edge of your
backyard pond will increase its value
and attractiveness. If you are using
a pre-formed liner for your pond, you
may want to build the wetland as described
above, with the water level slightly
above the pond liner or the edge of
the pond liner lowered a couple of inches
to allow water to flow into the pond.
This design filters sediment and other
contaminants out of the water coming
off your lawn or roof through the wetland
before it enters the pond. The wetland
area also protects fish and other aquatic
life in the pond by removing any chlorine
from city tap water you use.
Establishing
Plants:
The
plants you select for your wetland will
depend on:
length
of time the soil will be saturated or
covered with water,
depth of the water,
amount of sunlight on the site,
climate,
soil pH, and
size of the wetland.
Select plants that are hardy for your
area and provide the desired wildlife
habitat and aesthetics. The species
of plants most common in other wetlands
in your area with similar flooding cycles
will be easiest to grow and need the
least maintenance.
Choosing
and Establishing Plants for Ponds:
To
make part of your backyard like natural
wetlands, use a mix of diverse plants.
Most trees, shrubs, ferns, and many
other plants grow best in soils that
are only saturated early in the growing
season and after heavy rains. Others,
like the true bog plants, need almost
continually saturated soil. Plants like
water lilies need to be continually
flooded. Once established, plants like
cattails will thrive in water a couple
feet deep, but also in areas that are
wet for only short periods. However,
most have a narrower tolerance range
that may vary depending on where you
live. Always check with your local nursery
or other expert before making final
decisions on what varieties to plant.
Plants should always be purchased from
a reliable source.
Native
Trees Tolerant of Wet Soils:
Red
and silver maple (Acer rubrum, A. saccarinu
m)
River birch (Betula nigr a)
Catalpa spp.
Ash (Fraxinus sp p.)
Cottonwood (Populus deltoide s)
Swamp white oak (Quercus bicolo r)
Sycamores (Platanus spp.)
Native shrubs tolerant of wet soils:
Red osier dogwood (Cornus serice a)
Leatherwood (Dirca palustri s)
Winterberry (Ilex verticillat a)
Inkberry (Ilex glabr a)
Pussy willow (Salix discolo r)
Shrubby cinquefoil (Potentilla fruticos
a)
Native Herbaceous and Flowering Plants
for Sunny Moist or Boggy Conditions:
Cattails
(Typhus spp.)
Joe-Pye weed (Eupatorium maculatu m)
Great blue lobelia (Lobelia siphilitic
a)
Ironweed (Vernonia noveboracensi s)
Blue flag iris (Iris versicolo r)
Boneset(Eupatorium perfoliatum)
Cardinal flower(Lobelia cardinalis)
Goldenrods(Solidagospp.)
Marsh marigold(Caltha palustris)
Swamp milkweed(Asclepias incarnata)
Gentian spp.
Native Herbaceous and Flowering Plants
for Shady Moist or Boggy Conditions:
Bee
balm(Monarda didyma)
Arrowhead(Sagittaris latifolia)
False hellebore(Veratrum viride)
Turtlehead(Chelonespp.)
Skunk cabbage(Symplocarpus foetidus)
Royal fern(Osmunda regalis)
Netted chain fern(Woodwardia areolata)
Jack-in-the-Pulpit(Arisaema triphyllum)
Cinnamon fern(Osmunda cinnamonmea)
Shield ferns(Dropteris spp.)
Lady ferns(Athyriumspp.)
True bog plants requiring low pH and
sun:
Sundews(Droseraspp.)
Butterworts(Pinguicula spp.)
Pitcher plants(Sarracenia spp.)
Numerous other native wetland species
are available in most areas. There are
also many species that have been naturalized
in North America and are often considered
native plants. Unfortunately, some of
these species are more competitive and
have become invasive, crowding out the
native species that provide habitat
for indigenous wildlife.
Safety
Locate
the backyard wetland where it is unlikely
to attract unattended children. Check
local safety ordinances and building
ordinances for restrictions and permits.
On
the Farm
In
the rural landscape, wetlands filter
chemicals, excess nutrients, and sediment
from flowing water, protecting streams
and drinking water sources. They also
provide habitat for many wildlife species.
Across
the country, many farmers voluntarily
return formerly drained wetlands in
crop fields and pasture to fully functioning
wetlands. Many of these acres were marginally
productive and returning them to wetlands
provides significant ecological, economic,
water purification, and recreational
benefits.
Many
farmers enhance their wetlands with
nesting structures for ducks and other
birds, put in plants and annual seeding
to provide winter food and cover for
wildlife, and establish native wildflowers
to make the landscape more attractive.