Phalaris arundinacea; Originally brought over to be forage for livestock, this grass quickly spreads and only the young tender growth is palatable to most animals. This plant can grow in inundated soils and spreads by seeds and creeping rhizomes. without mechanical control, this plant generally outcompetes native species.

Native to Eurasia

3-6’

Class C

Polygonum cuspidatum; One of the most aggressive invasive species in Western Washington and one of the most difficult to control. Japanese Knotweed creates a dense monocultural hedge that crowds out other vegetation and degrades habitat. Often found along roadways and riverbanks, it spreads via seed and rhizomes which must be disposed of delicately because new plants can sprout from very small cuttings.

Native to Asia

4-8’

Class B

Rubus armeniacus; Probably our most celebrated invasive species. It offers delicious berries that endear itself to us in the middle of summer. The plant itself is a nightmare: It is an aggressive spreader that sends out thick canes that are covered with sharp strong prickles. If unmanaged, it can create impenetrable hedges and can easily overtake our native herbaceous and small shrub plants.

Native to Asia

Can create hedges 10-15’

Class C

Circium vulgare; Bull Thistle is an aggressive, spreading herbaceous perennial plant with thorny barbs on the tips of its leaves. It has a beautiful bloom that is great for pollinators but this plant has a tendency to colonize pastures and other disturbed sites and crowd out native herbaceous plants and grasses. Most livestock do not eat it.

Native to Europe, Asia & North Africa

4-6’

Class C

Hedera helix; English Ivy can cover the ground, overwhelm native habitat and climb trees and eventually kill them by strangling and offering them no sunlight. The flowers are a wasp favorite and the berries are spread by birds. The sap can cause rashes and skin irritations. Ivy vines grow air roots that anchor to its host and removing the ivy can damage the plants and trees around it. Care must be taken when removing.

Native to Europe, Asia & North Africa

Berries & leaves are toxic to humans and cattle

Class C

Crataegus monogyna; Also called One Seed, Common or Red hawthorn, it is a long lived deciduous small hardwood tree that can form thickets that don’t allow any sunlight to reach the ground, which restricts herbaceous growth. Don’t get it confused with the wonderful native Douglas Hawthorn, Crataegus douglasii. The leaves are slightly different but the easiest way to tell them apart is the invasive species’ berries stay red, whereas the native Hawthorn berries turn black or dark purple when ripe. Hawthorn is in the pomme family, same as apple and pear. One management technique that could be fun is to cut the tops off all invasive Hawthorn and graft apple and pear scionwood to the rootstock. Boom, quick orchard!

Native to Asia, Europe & North Africa

10-20’

Class C

Cirsium arvense; Very similar to its relative Bull Thistle, Canada Thistle spreads rhizomatically and by seed so it can quickly create monocultural patches that are inedible by livestock. It can spread into pastures, disturbed areas and can handle wetter soils, making it a common adversary in Western Washington.

Native to Europe & Asia

2-5’

Class C

Iris pseudacorus; An escaped garden ornamental, Yellow Flag Iris is commonly found in wet to fully inundated soils and grows in a clumping form. The sap can cause skin irritation.

Native to Europe & Mediterranean region

1-3’

Toxic to humans and livestock

Class C

Buddleja davidii; Butterfly bush is still commonly sold in retail nurseries and planted in gardens. Unknown to the common gardener but this plant easily escapes cultivation and can form dense thickets and push out native plants, wreck wildlife habitat and alter nutrient availability in soils. There are sterile varieties available here: Buddleja Approved Cultivars

Native to China

8-16’

Class B

Epilobium hirsutum; Commonly found in unmanaged wetlands, Hairy Willow Herb is another escaped garden ornamental. It has beautiful pink flowers that bloom in the middle of summer. This plant spreads by windblown seed and aggressive rhizomes.

Native to Afica, Asia & Europe

3-6’

Class B

Cytisus scoparius; Scotch Broom quickly spreads and displaces native plants and habitat and forms monocultures. It also is allelopathic which means that it releases chemicals that kill or disrupt the growth of plants near it. Scotch Broom also has oils that are extremely flammable and can be a fire hazard. This plant is commonly seen on the side of highways in high and dry growing spaces

Native to Europe

3-10’

Toxic to livestock

Class B

Tanacetum vulgare; A member of the Aster family, Tansy is an herbaceous perennial that grows abundantly in pastures and isn’t commonly grazed. It has a strong aromatic quality and is toxic to humans and livestock. Tansy can adapt to many Western Washington environments and spreads vegetatively and via seed. It is commonly mistaken for Tansy Ragwort, another class B invasive species.

Native to Asia & Europe

2-4’

Toxic to humans & livestock

Class B

Geranium robertianum; Stinky Bob! If you step on this plant or squish it in your hands you’ll know why it has this nickname. This is an unassuming invasive species. It looks cute and delicate but it has a tendancy to overtake native understory plants and its ability to grow in full shade makes it difficult to eradicate without intervention.

Native to Europe, Asia & North Africa

Up to 1’

Class B

Conium maculatum; Don’t touch it, don’t look at it, don’t breathe near it. I’m not exaggerating that much either, this plant is really toxic and has incredible self defense mechanisms that make management difficult. It is very adaptable to our region and can be found in open meadows, pastures and disturbed areas. They are a member of the carrot family and can be mistaken as a wild carrot but the purple specks on the stem are a quick way to properly identify.

Native to Europe, Asia & North Africa

5-10’

Toxic to humans & livestock

Class B