Download The Most UNWANTED Invasive Garden Plants

Credit Valley Conservation
The Most UNWANTED Invasive Garden Plants
T he following plants are those that
first appear as welcome additions
to your garden, but soon can become
unwieldy, wild and aggressive. They are
most dangerous when planted next to
natural areas where they endanger and
threaten native species by crowding
them out and by altering local environmental conditions.
Please see our website for more information
on planting alternatives, identification tools
and for other information at:
www.creditvalleyca.ca/invasives
Useful links:
Ontario Invasive Plant Council at www.ontarioinvasiveplants.ca
Ontario Federation of Anglers and
Hunters Invading Species Awareness
Program at www.invadingspecies.com
1 Curly pondweed (Potamogeton crispus)
A submerged aquatic plant with alternating
leaves having wavy margins that are distinctly sharp toothed when examined closely.
Leaves are also green to rust brown in colour.
Curly pondweed spreads primarily by plant
fragments and seed. Flowers are not showy,
are rust-brown in colour and appear on an
emergent spike above the water surface.
2 English ivy * (Hedera helix)
This is a herbaceous vine and groundcover.
Alternating leaves are three lobed with lighter
coloured veins against a dark green glossy
leaf. English ivy spreads primarily through
creeping roots and branches.
3 Eurasian watermilfoil (Myriophyllum spicatum)
This is a submerged plant of aquatic
gardens with feather-like leaves arranged
in whorls around a central stem. It can be
easily confused with native watermilfoils.
Eurasian watermilfoil spreads primarily by
segments breaking off, but also by seed. Small pink/whitish flowers emerge on a stalk
above the water.
4 European frog-bit (Hydrocharis morsus-ranae)
This is a floating-leaved aquatic plant similar
to a water lily. Leaf and stem are similar to
floating heart but more rounded in shape and
with a smooth (not wavy) margin. It spreads
primarily by roots and plant fragments, but
also by seed. Flowers have three white petals
and are larger than a 25 cent coin.
5 Floating heart (Nymphoides peltatum)
This is a floating-leaved aquatic plant similar
to a water lily. Heart-shaped leaf with stem
attached near the slit where the two lobes
meet. Leaf edge is smooth with slightly wavy
margins. It spreads primarily by roots and
fragments, but also by seed. Flowers are
about the size of a dollar coin, with five petals
that are yellow with a crinkled/wavy edge.
6 Flowering rush (Butomus umbellatus)
This is an emergent aquatic plant with grasslike long leaves that are triangular in cross
section and corkscrew slightly at the tip. It
spreads by root fragments, bulbils and seed.
Attractive small pink flowers are in a bowl-like
cluster on separate stalks.
7 Giant hogweed (Heracleum mantegazzianum)
This is a tall (2 to 4 m) herbaceous plant
with very large (1 to 2 m) deeply divided/
lobed alternating leaves. The stem is hairy
and very robust with purplish spots. It is
poisonous to touch (phototoxic burns) and
spreads primarily through seed. It has small
white flowers in a bowl-like cluster atop each
individual plant. Can be confused with the
native plant, Cow parsnip.
8 Goutweed (Aegopodium podagraria)
This is a herbaceous plant and groundcover.
The plant has variegated white and green
leaves that alternate along the stem. Naturalized plants often lose this variegation. It
spreads primarily by roots, but also by seed.
Goutweed has small white flowers in a bowllike cluster on a single stalk.
9 Himalayan balsam (Impatiens glandulifera)
This is a tall (1 to 2 m) herbaceous plant with
fleshy pink-reddish stems and a lance-shaped
alternating leaf with saw-tooth like edges. It
spreads primarily by seed and has irregular
cone-shaped pink flowers.
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10 Japanese knotweed (Polygonum cuspidatum)
This is a tall (1 to 2 m) herbaceous plant with
a tear drop shaped leaf that has a flattened
bottom. Leaves are alternate. Stems are
robust and look like bamboo when mature.
Japanese knotweed spreads primarily by
roots, but also by seed. Flowers are small,
green-white and arranged on elongated
clusters along the stem.
11 Miscanthus, Eulalia (Miscanthus
sinensis and M. sacchariflorus)
This is a tall clumping grass with reed-like
stems that can be 1 to 4 m high. The flower
heads are feathery or plume-like. In late
summer the flower heads turn reddish, then
pinkish then matures to a slivery colour. Leaf
blades are approximately 2.5 cm wide and
have a distinct white midrib. In the fall, leaves
turn to a tan/yellow colour. Cultivated varieties,
such as ‘Porcupine’ and ‘Zebra’, which grow
taller than 2 m, are not known to produce
viable seed and therefore don’t spread.
12 Non-native honeysuckles (Lonicera species)
These are all woody shrubs (2 to 4 m) with
brittle/weak stems. Bark is light coloured and
papery and can be scraped off easily with a
fingernail. Opposite leaves are egg-shaped
or lance-shaped and hairy on some species.
This plant spreads primarily through seed,
but also by roots. Flowers are irregular and
showy and a variety of colours. Fruits appear
as two small red berries fused together. There
are also many native honeysuckles that could
be confused with these species. See CVC
website for more detail and a list of specific
species considered invasive.
13 Norway Maple (Acer platanoides)
This deciduous tree is sometimes difficult to
distinguish from native sugar maple. Norway
maple spreads by seed. Leaves are opposite
and five-lobed, often with a slight purple tinge,
often affected by black spot fungus late in the
season. Milky sap can be seen exuding from
leaf stem if picked and squeezed. Winged
seeds can be seen to form a T-like shape
when attached to the stem.
14 Periwinkle * (Vinca minor)
This is a distinctive herbaceous groundcover
with opposite bright green, lance-shaped
shiny leaves. Periwinkle spreads primarily by
roots and has purple flowers with five petals.
15 Rough manna grass (Glyceria maxima)
This is a tall grass (1 to 2 m) often sold in
a variegated variety, most often for aquatic
gardens. Rough manna grass loses this
variegation when naturalized. Stem sheaths
near the base have a slightly rough/sticky
feeling to the touch and are oval or flattened
in cross-section. Base of the plant is often
red/purple in spring. It spreads by seed and
roots. Flowering head of this grass is fine and
cascading, not showy.
16 Winged euonymus (often sold as
Burning bush) and Spindle tree
(Euonymus alatus and E. europaeus)
These are woody shrubs with opposite
finely toothed lance-shaped leaves. Young
stems are distinctly green in colour. Winged
euonymus have distinct ridges/wings on stem
and spread primarily by seed. Flowers are not
showy and are whitish/greenish. Seeds are
distinct with winged euonymus, having twoparted bright red fruit and spindle tree with a
four-parted pink/red fruit.
* Spreads primarily by roots; can be contained if planted and managed away from a natural area.
The other plants spread by root and seed. They are a risk if planted anywhere. To report one of these invasive plants or for assistance and possible funding to remove contact CVC at 1-800-668-5557, 905-670-1615 or visit: www.creditvalleyca.ca