4
Invasive Wetland Plants
A number of ornamental plants
once recommended for water
gardens or moist garden soil have
spread to our riverbanks, flood
plains, and wetlands.
They are extremely difficult to
eradicate once established – up to
10 years of repeated treatment
may be needed to remove Purple
loosestrife or
Phragmites
. These
plants propagate by seed and by
fleshy root parts which break off
easily. Both are spread by water,
feet (human, animal, bird), and
tires, including those of mowers.
They are also found in dredge spoil,
fill dirt, and compost. it is not
clear whether seeds may be
transported by wind.
Do not plant exotic water
garden plants unless they are
not hardy, and never dump plants
from fish tanks or water gardens
into toilets, storm drains, lakes,
or streams.
Common Reed
(Phragmites
australis,
formerly
P. communis)
looks like a tall ornamental grass
with lovely plumes, usually white or
tan.
Although the species is
indigenous, a particularly
aggressive strain, probably
introduced or a hybrid, has
escaped from natural controls and
taken over many formerly diverse
wetlands. It is also seen in
roadside ditches.
Control: (10) or (11), using Rodeo
when the plant is flowering. If
possible, follow-up with a
controlled burn of the dead plants,
to allow native plants to return.
Do not dig Phragmites – the
roots will break, re-sprout, and
spread. If herbicide cannot be
used, cut annually in late July to
reduce spread.
Giant Reed (
Arundo donax
)
chokes waterways from Virginia
south. It can grow 20' tall.
Control: same as for Phragmites
or mow several times a season.
Japanese Knotweed, Mexican
Bamboo (
Polygonum cuspidatum
)
can grow in shade. The stems have
knotty joints, reminiscent of
bamboo. It grows 6-10' tall and
has large pointed oval or
triangular leaves.
Control: cut at least three
times each growing season and/or
treat with Rodeo (10) or (11). In
gardens, heavy mulch or dense
shade may kill it.
Purple Loosestrife (
Lythrum
salicaria, L. virgatum
), a
handsome garden plant, has tall
spikes of magenta flowers over a
long bloom season.
Often marketed as sterile, it is
at best self-sterile, i.e., it can be
pollinated by plants you may not
be aware of, growing nearby.
A single plant can produce up to
a million seeds. Like Phragmites, it
chokes out all competitors and
has taken over millions of acres of
wetland in the U.S.
Control: initial infestations may
be hand-pulled (1) before flowering
(do not dig). Bag and burn or send
to the landfill. Otherwise, use
Rodeo (10) or (11) when plants
begin to bloom (they continue to
flower while setting seed). Expect
to re-treat for several years until
the seed bank is exhausted.
Lesser Celandine, Celandine
Buttercup (
Ranunculus ficaria
)
has spread from gardens to
carpet our flood plains with small
yellow flowers in spring.
It comes up in winter, giving it a
head start over most native
spring wildflowers.
Control: it is not yet known
whether digging is effective – the
small reproductive corms break off
very easily.
Try digging (1) before the plants
flower. Otherwise, use Rodeo (10 or
11), preferably in February to
protect native plants, frogs, and
salamanders which become active
in March.
Recommended Native Wetland
Plants for Water Gardens
s
Turtlehead
(Chelone glabra)
s
Lizard’s tail
(Saururus cernuus)
s
Cardinal flower
(Lobelia cardinalis)
s
New York ironweed
(Vernonia noveboracencis)
s
Blue flag (Iris versicolor)
s
Virginia bluebells
(Mertensia virginica)
s
Wild blue phlox
(Phlox divaricata)
s
Arrowhead
(Sagittaria latifolia)
s
Pickerelweed
(Pontederia cordata)
s
Also use native reeds, rushes,
and sedges.
