28 Invasive Plants to Avoid in the Pacific Northwest
Do you live in the Pacific Northwest and want to grow a healthy landscape without any invasive species? Invasive plants can take over your garden, invade nearby natural areas, and compete with native species. In this article, gardening expert Liessa Bowen shares 28 invasive plants you should not introduce into your yard or garden.
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In a balanced and healthy ecosystem, a diverse community of plants coexists. These plants may include trees, shrubs, grasses, forbs, ground covers, ferns, water plants, and more. Some plants may be more dominant than others, but rarely does one completely dominate the landscape. When invasive plants enter into the Pacific Northwest’s ecosystem, they upset the natural balance.
The biggest problem is that invasive species grow and spread rapidly. They can easily dominate a landscape. They outcompete native plants, reduce biodiversity, and harm native fauna.
If you already have invasive species in your yard, it’s never too late to remove them. It will take a lot of work (these plants are good at dominating!), but the time and effort will keep your garden from a takeover. You can help prevent the spread of invasives by not buying or planting them in your garden.
Learn to identify the most common invasive plants in your region so you can be proactive if they start invading your yard. Let’s learn about 28 invasive plant species you should dig out (and not plant!) in your Pacific Northwestern garden.
Butter and Eggs
Butter and eggs (Linaria vulgaris), also known as yellow toadflax, and other toadflax plants (Linaria spp.) are herbaceous perennials native to Eurasia. Butter and eggs was introduced as an ornamental garden plant but has spread, naturalized, and become invasive in many states across the United States.
This plant tolerates a wide range of growing conditions and quickly colonizes roadsides, fields, meadows, and pastures. Plants spread by rapidly expanding vegetative growth and by freely self-seeding.
Alternative: For a similar-looking but non-invasive garden plant, choose snapdragons (Antirrhinum majus) or the native plant Oregon sunshine (Eriophyllum lanatum) for their showy blooms.
Butterfly Bush
Butterfly bush (Buddleja davidii) is a deciduous shrub native to China and Japan. Unfortunately, its showy flowers make it a popular choice at garden centers. While it attracts butterflies, it cannot host their young and takes over areas where their host plants could grow.
This plant can easily escape cultivation, spreads rapidly, and displaces native plants. Butterfly bush reproduces readily by self-seeding. It is fast-growing and can reach the flowering stage within the first year of germinating from seed.
Alternative: There are plenty of attractive flowering shrubs you could grow instead of butterfly bush. Try the native flowering red currant (Ribes sanguineum) or native elderberry (Sambucus spp) instead. These plants have beautiful flowers and attract plenty of pollinators.
Cherry Laurel
Cherry laurel (Prunus laurocerasus) is a large shrub native to southern Europe and southwestern Asia. Gardeners often use this plant for privacy hedges or windbreaks. Cherry laurel has glossy green leaves and blooms in the springtime, with small, dark purple fruits following in mid-summer.
Cherry laurel grows primarily in moist woodlands and spreads by seed dispersal. It can displace native vegetation in forests, open woodlands, and along forest edges.
Alternative: If you are looking for an attractive shrub that is not invasive, try growing evergreen huckleberry (Vaccinium ovatum) or red huckleberry (Vaccinium parvifolium) instead.
Cornflower
Cornflower (Centaurea cyanus), or bachelor’s button, is an annual flowering plant native to Europe and western Asia. You’ll find it frequently in flowering seed mixes because it is showy, grows fast, blooms quickly, and tolerates various growing conditions.
Unfortunately, this makes it a prime candidate for being aggressive, particularly in open meadows and fields. This plant can reseed itself very effectively and spread quickly to create dense clusters.
Alternative: Try some native flowering plants instead, such as showy fleabane (Erigeron speciosus) or low beardtongue (Penstemon humilis). These plants are easy to grow, and pollinators love them!
English Holly
English holly (Ilex aquifolium) is a large evergreen holly native to Europe, western Asia, and northern Africa. It has been imported as a landscaping tree but has escaped cultivation and naturalized throughout large regions of the Pacific Northwest.
It produces abundant red fruits eaten and distributed by birds and other small animals. English holly is tolerant of various conditions and has invaded forests, open woodlands, and along waterway edges. Young seedlings are easy to remove, but once established, the larger trees are difficult to control because they will regrow from stumps and healthy roots.
Alternative: As an alternative to the English holly, try growing the native Pacific wax myrtle (Myrica californica) instead. Pacific wax myrtle is an evergreen shrub with pleasantly scented leaves.
English Ivy
English ivy (Hedera helix) is a hardy, adaptable, and easy-to-grow plant native to Europe. English ivy has insignificant flowers but produces small dark purple berries that birds eat and distribute far and wide.
It is a ground cover that quickly outcompetes and buries native vegetation, diminishing the natural species diversity of an area. English ivy can rapidly cover large areas of ground and climb up trees, walls, fences, structures, and shrubbery.
Alternative: If you want a native replacement for English ivy, try coastal strawberry (Fragaria chilensis), an evergreen, fruit-producing groundcover.
European Hawthorn
European hawthorn (Crataegus monogyna) is a deciduous shrub or small tree native to Europe, northwestern Africa, and western Asia. It is a common ornamental landscaping plant for its attractive foliage, flowers, and berries.
It grows dense masses of thorny branches and blooms in the springtime with white blossoms. This plant primarily spreads because birds eat the fruits and disperse the seeds far and wide. European hawthorn has invaded open forests, woodlands, pastures, and grasslands.
Alternative: Douglas hawthorn (Crataegus douglasii) is a beautiful native shrub. The spring-blooming white flowers are showy, and birds love the fall fruits.
European Mountain Ash
European mountain ash (Sorbus aucuparia), also known as rowan-berry, is a small tree native to Europe and western Asia. It grows in sunny locations and produces showy clusters of reddish-orange fruits. Birds eat the fruits and then spread the seeds into nearby woodlands, fields, and roadsides.
European mountain ash grows easily from seed and tolerates various growing conditions. As it escapes cultivation, it competes with native vegetation and spreads freely.
Alternative: If you are looking for a showy native tree, try growing bitter cherry (Prunus emarginata) for its bright red fruits and beautiful yellow fall foliage.
Fragrant Waterlily
Fragrant waterlily (Nymphaea odorata), also known as the American white waterlily, is a great example of a plant native to the United States yet considered an invasive species in some states beyond its native range. It forms dense blankets of vegetation in lakes and ponds, outcompeting native vegetation and blocking water access.
This invasive plant has roots at the bottom of shallow bodies of water, with floating leaves and flowers that bloom in the summertime. The flowers are showy and fragrant.
Alternative: The native watershield (Brasenia schreberi) is a much better choice for your Pacific Northwest garden ponds.
Himalayan Blackberry
The Himalayan blackberry (Rubus armeniacus) is a shrubby plant native to Eurasia. It produces numerous thorny stems that quickly become impenetrable thickets. Himalayan blackberry blooms in the springtime with clusters of pinkish-white flowers, soon followed by sweet, juicy, black fruits.
Birds and other small animals eat the fruits and help spread the seeds. However, these plants will cover large areas with vegetative growth alone.
Alternative: If you want a fruiting shrub for your landscape, grow the native salmonberry (Rubus spectabilis) or a non-invasive marionberry (Rubus ‘Marion’) instead. There’s no reason to choose an invasive species when there are better options that benefit animals and the natural environment.
Indigo Bush
Indigo bush (Amorpha fruticosa), also called false indigo, is a deciduous shrub native to the southeastern United States. It grows quickly and can be aggressive, particularly along waterway edges, open woodlands, and roadsides. Though it has unique flowers, this plant forms dense colonies that crowd out native vegetation.
Alternative: Indigo bush has showy flowers that attract butterflies, but there are better choices that are non-invasive in the Pacific Northwest. If you’re looking for something with bright, showy flowers to brighten your landscape, consider growing a spring-blooming azalea bush instead.
Japanese Honeysuckle
Japanese honeysuckle (Lonicera japonica) is a fast-growing vine native to eastern Asia. Japanese honeysuckle was first introduced as an ornamental landscaping plant and has since naturalized widely throughout the United States. This woody perennial vine is either evergreen or semi-evergreen, depending on the climate where it grows.
This vining plant can grow in widely varied conditions and produces fragrant, tubular, creamy white flowers. Once established, removing it can be challenging because it spreads by seed and prolific root sprouts.
Alternative: Western trumpet honeysuckle (Lonicera ciliosa) is a beautiful native vine that will attract hummingbirds and insect pollinators with its showy bright orange flowers.
Knotweed
Knotweed (Polygonum cuspidatum) is an extremely invasive plant that originated in Asia. Originally an ornamental plant, it can be used for erosion control. It is now widespread across the United States.
It tolerates various conditions but is particularly problematic near wetlands where it forms dense colonies, outcompetes native vegetation, and dramatically alters native plant communities.
Knotweed is an herbaceous perennial that becomes large and shrublike. It blooms in the spring and summer months, followed by seed pods. Plants spread and colonize quickly by vegetative growth and self-seeding. Once established, knotweed is very difficult to remove because any remaining section of root that is not removed will simply re-sprout.
Alternative: Mock orange (Philadelphus lewisii) is a great native plant. Enjoy its beautiful clusters of white, pollinator-friendly flowers.
Old Man’s Beard
Old man’s beard (Clematis vitalba) is a highly invasive vine native to Eurasia. It was introduced to the United States as an easy-to-grow ornamental plant. Unfortunately, it can quickly escape cultivation and cover native vegetation with a thick blanket of growth.
Old man’s beard produces copious white flowers, followed by thousands of wind-blown seeds. These seeds help spread this plant well beyond its intended plantings.
Alternative: If you want a beautiful flowering clematis, choose the native western clematis (Clematis ligusticifolia) instead. Western clematis has beautiful creamy white flowers that bloom in late summer and attract many pollinators.
Orange Hawkweed
Orange hawkweed (Hieracium sabaudum) is an herbaceous perennial introduced from Europe. Hawkweed can look pretty in the garden, but it is very difficult to control as soon as it goes to seed. There are multiple varieties of invasive hawkweeds, and all can spread aggressively by wind-blown seeds that look similar to dandelions.
As it spreads, it outcompetes native plant species and reduces biodiversity in that area. Once it escapes cultivation, it easily colonizes roadsides, open fields, meadows, and hillsides.
Alternative: Try growing California poppy (Eschscholzia californica) as a beautiful native alternative with extremely showy flowers.
Parrotfeather
Parrotfeather (Myriophyllum aquaticum) is a water plant commonly found in slow-moving waterways, ponds, and wet ditches. This plant has been introduced as an ornamental pond plant but is detrimental to the native ecosystem. It grows quickly and densely, choking out native vegetation and clogging waterways with almost impenetrable growth.
Parrotfeather is hardy and difficult to remove once it becomes established. It can regenerate new plants from broken stem sections and spread freely as waterways flood and water flows from one waterway to the next.
Alternative: If you are looking for a great wetland plant, try the native water plantain (Alisma subcordatum) as an attractive water plant for your pond.
Pokeweed
Pokeweed (Phytolacca americana) is a fast-growing herbaceous perennial native to the southeastern United States. While technically, this plant is native to North America, it has very aggressive tendencies and, once established in an area, is difficult to control.
It spreads by thick tuberous roots and also a prolific output of seeds that birds eat. Because birds disperse the seeds, most people unexpectedly discover pokeweed in their landscapes rather than intentionally plant it.
While the plants are fairly attractive with their bright red stems and dark purple berries, pull them before they become too comfortable in your yard. Be sure to wear gloves when working with pokeweed; some people develop a blistering rash from handling this plant.
Alternative: Bugbane (Actaea elata) is a native woodland wildflower. It has beautiful spikes of white flowers and thrives in moist, shaded locations.
Policeman’s Helmet
Policeman’s helmet (Impatiens glandulifera), also known as ornamental jewelweed, is a flowering annual native to India and the western Himalayas. This plant can commonly be grown from seed and is sometimes included in flower seed mixes.
If you already have this plant growing, remove it or at least deadhead spent flowers to prevent them from producing seeds. It can easily escape cultivation, dispersing seeds through its explosive seedpods. It then colonizes roadsides, waterways, and moist forested areas.
Alternative: Red columbine (Aquilegia formosa) or scarlet gilia (Ipomopsis aggregata) are great alternatives with their showy red flowers that pollinators will love.
Purple Pampas Grass
Purple pampas grass (Cortaderia jubata) is an invasive ornamental grass originating in South America. This tall perennial grass is tolerant of a wide variety of environmental conditions, soil types, and moisture levels, allowing it to invade many natural habitats quickly.
Purple pampas grass creates dense stands in coastal areas, ditches, and along roadways, choking out native vegetation and creating dry fuel for wildfires.
Alternative: For more well-behaved ornamental grasses, try the native Idaho fescue (Fescuta idahoensis) or California fescue (Fescuta californica) as alternatives to pampas grass.
Purple Loosestrife
Purple loosestrife (Lythrum salicaria) is a familiar wetland plant native to Europe and parts of Asia. It is very showy and beautiful, but unfortunately, in many northern states, it is also very effective at choking waterways and crowding out native plants.
Purple loosestrife reproduces prolifically by seed and can completely fill wet meadows, shallow lakes, marshes, and streamsides. This plant becomes very difficult to control once it becomes established, in part because it can reproduce so quickly but also because it occupies wet and saturated soils, which are difficult to access.
Alternative: If you are looking for a well-behaved plant to grow in a wet location, try the native red elderberry (Sambucus racemosa) and enjoy its showy, bright red fruits.
Russian Olive
Russian olive (Elaeagnus angustifolia), also known as oleaster, is native to parts of Europe and Asia. This small deciduous tree was introduced as a hardy shrub for landscaping and ecological reclamation projects.
It blooms in the summertime and produces fruits in fall. Birds eat and distribute the fruits, allowing these plants to spread quickly. They also spread aggressively within an area by suckering. Russian olive is now extremely widespread throughout the United States and is widely considered a weedy and invasive species.
Alternative: Are you looking for an attractive small tree? Try the native bitter cherry (Prunus emarginata) instead. Bitter cherry produces beautiful clusters of white flowers in the spring, followed by edible red fruits in the summer months.
Saltcedar
Saltcedar (Tamarix ramosissima), also known as tamarisk, is native to Eurasia. It has been used as erosion control and a landscaping tree because it is easy to grow and provides ornamental value with its abundance of showy pink flowers. Saltcedar is tolerant of many soil and light conditions, allowing it to grow and spread quickly.
These plants most commonly invade waterway edges, drainage ditches, and along lakeshores. They spread by producing massive numbers of seeds each year, as well as being able to root from broken stems and root segments. It is now widely distributed throughout the United States, particularly in riparian areas.
Alternative: Replace saltcedar with the native narrowleaf willow (Salix exigua) for a more sustainable option.
Scotch Broom
Scotch broom (Cytisus scoparius) is a medium-sized shrub native to parts of Europe and northern Africa. It was introduced to North America as an ornamental shrub and used for landscaping and erosion control. It thrives in full sun and tolerates various soil conditions, making it easy to grow.
Scotch broom has become invasive in dry grasslands, hillsides, open woodlands, dry riverbeds, and pastures. It produces numerous flowers, which, in turn, produce numerous seeds, allowing it to spread quickly. It also spreads by root suckers, making it impossible to remove simply by cutting down unwanted plants.
Alternative: If you are looking for an ornamental shrub for your landscape, try Oregon grape (Berberis nervosa or Berberis aquifolium) instead.
Shining Geranium
Shining geranium (Geranium lucidum) is an annual plant with small, pink, five-petaled flowers. The leaves are rounded with deeply cut lobes at the end of bright red stems. The plants grow in low, leafy rosettes, making a very effective ground cover.
Shining geranium grows primarily in moist, shaded woodlands. Unfortunately, this ability to form a dense ground cover also allows the shining geranium to choke out native vegetation. Dense carpets of this plant spread by self-seeding.
Alternative: If you would like a beautiful, shade-loving plant for your woodland garden, choose the native wild bleeding heart (Dicentral formosa) instead. If you prefer a non-invasive ornamental geranium, check out the cranesbill geranium (Geramium sanguineum).
Spurge Laurel
Spurge laurel (Daphne laureola) is an evergreen shrub native to parts of Europe. It has thick, glossy leaves and grows as a small to medium-sized understory plant in moist forests. This plant was introduced as an ornamental landscaping plant but has become invasive in the Pacific Northwest.
Spurge laurel spreads by root suckering and seeds, creating dense stands and outcompeting native species. Be careful if handling spurge laurel because the leaves and stems contain toxins that can irritate the skin.
Alternative: As an alternative, consider growing the red-osier dogwood (Cornus sericea) as an appealing native plant for shaded landscapes.
Tree of Heaven
Tree of Heaven (Ailanthus altissima) is a very widespread invasive species. It is a medium to large-sized tree that is native to northern China. Tree of Heaven has been used as a landscaping plant because it grows quickly in challenging site conditions.
Unfortunately, it also spreads quickly and aggressively by self-seeding and root suckers, forming dense stands and choking out native vegetation.
Alternative: Smooth sumac (Rhus glabra) is a shrub that grows 10 to 20 feet tall. In midsummer, it has showy pale yellow flowers followed by prominent clusters of red, fuzzy-looking berries that persist through the fall and into winter. Smooth sumac has attractive, pinnately compound leaves that turn brilliant shades of red in the fall.
Yellow Archangel
The yellow archangel (Lamium galeobdolon) is an herbaceous perennial native to Europe and western Asia. Yellow archangel is an ornamental landscaping plant, appreciated for its attractive foliage and showy yellow flowers.
Unfortunately, this plant can also escape cultivation, naturalize, and become invasive, particularly in forests of the Pacific Northwest. Yellow archangel is a member of the mint family and spreads rapidly by self-seeding and vegetative sprawl, rooting as stems creep and touch the ground.
Alternative: If you are looking for a native ground cover for a shaded location, try Salal (Gaultheria shallon), which has attractive white flowers that support hummingbirds, butterflies, and bees.
Yellow Flag Iris
Yellow flag iris (Iris pseudacorus) is a water-loving iris native to Europe and northern Africa. It grows at the edges of lakes, ponds, and wetlands, forming dense colonies.
Rhizomes and prolific self-seeding spread yellow flag iris far and wide. The seeds can float to other locations during high water and flooding, allowing this plant to spread beyond a single body of water.
Yellow flag iris has been used as an ornamental water plant. Still, it has naturalized in many areas across the United States, being declared an invasive species in several states, primarily in the northwestern and northeastern states.
Alternative: As an alternative to the yellow flag iris, grow the native Douglas iris (Iris douglasii) or the ornamental Japanese iris (Iris ensata) for beautiful, non-invasive, moisture-loving plants.
Frequently Asked Questions
Is there a way to grow invasive species safely in my yard?
If, for some reason, you absolutely must grow an invasive species in your yard, do so with great care. Some plants are forbidden to grow in certain states, so check what rules apply to you based on your location.
Many invasive species spread by vegetative growth (e.g., rhizomes) and vigorous self-seeding. Grow your plant in a container and deadhead any spent flowers to prevent the plant from spreading beyond its container. Ideally, grow something native or non-invasive instead, and know you’re creating the healthiest garden you can!
If my flowering invasive species attracts butterflies, isn’t that a good thing?
It’s always nice to offer nectar to the local pollinators, but there are better ways to do it than with invasives like Butterfly bush. Butterflies have adapted to co-exist with the native plants of the region, so there are plenty of great native options that pollinators love.
Many native plants also provide a caterpillar food source for butterflies, so you can support more than one part of the butterfly life cycle. There are plenty of interesting non-native, but non-invasive, plants that are also good pollinator plants.
Do I have to remove invasive plants that are already in my yard?
Many yards and natural areas already have at least one invasive species. Invasive plants are common and widespread. If you already have some growing, they may be a nuisance in your yard. If you hope to create a healthy landscape, you need to remove the invasive species. You’ll be battling a plant with very aggressive growth, but in the long run, removing the invasive species will help you grow a better garden.
Final Thoughts
Gardening can be a great joy, but battling invasive plants is time-consuming and frustrating. As you select plants to grow in your garden and landscape, avoid buying or planting any invasive species. Choose well-behaved cultivated plants and native plants whenever possible.
When you grow a healthy and well-balanced garden full of beautiful native plants and non-weedy cultivated varieties, you’ll know you are creating the best mini-ecosystem you can to benefit the environment, pollinators, and yourself.
