Invasive Plants in Ontario & What to Plant Instead
Beautiful Native Alternatives to 25 Invasive Garden Plants
Lily of the Valley is a charming but highly invasive non-native plant sold in nurseries across Ontario.
I often find myself walking through picturesque Ontario trails, soaking in the beauty around me, only to realize that much of the greenery isn’t as innocent as it seems. Since learning to identify invasive and noxious weeds, I’ve been stunned by how many are all around us, in urban and suburban spaces as well as in protected areas! From the deceptively pretty creeping bellflower to the fast-spreading garlic mustard, these plants are wreaking havoc on Ontario’s ecosystems. The kicker? Many are still sold in nurseries across Ontario, readily spreading into our wild areas.
What Are Invasive Plants?
Let’s first get clear on definitions:
Native plants are those that have evolved in a certain eco-region over millennia, if not eons. They are perfectly adapted to their area and essential to the ecosystem. They have specialized relationships with local pollinators, like insects and birds, and are the foundation of local food webs.
Pictured right is Wild Lupine (Lupinus perennis), a gorgeous native perennial that supports Ontario native bees and butterflies.
Non-native or “exotic” plants do not occur naturally in a specific region, but were introduced due to human activity. Non-native plants may or may not pose a threat to native plant species. However, having not evolved in the eco-region, they do not support local food webs as well as native plants do.
“Naturalized” plants are non-native plants that have successfully reproduced in their new environment. They may or may not pose a threat to native plant species. But, having not evolved in the eco-region, they most often do not support local ecosystems as well as their native counterparts do.
Invasive plants are non-native plants that cause harm to native biodiversity, the economy and/or human health. They may outcompete or harm native plant species, impacting wildlife and ecosystem function. By this definition, even vigorous native plants that spread easily can not be considered invasive.
Noxious weeds are plants designated by a governing authority as harmful to ecosystems, crops, livestock, or human health. They are often invasive plants that a governing body is attempting to regulate. In Ontario, noxious weeds are listed in the Schedule of Noxious Weeds under the Weed Control Act. Homeowners have a legal obligation to remove noxious weeds, so it’s important to get familiar with them. Here is a list of Ontario’s noxious weeds.
Pictured left is Coltsfoot (Tussilago farfara), a noxious weed I commonly find along trails in public parks and protected areas in Ontario.
Impacts of Invasive Plants
The International Union for the Conservation of Nature ranks invasive species as one of the most important threats to biodiversity, second only to habitat loss. These aggressive plants often have no natural predators to keep them in check. Once they get a foothold, they can spread vigorously, wreaking havoc on entire ecosystems. The consequences can be devastating and often permanent, or at least very difficult and costly to reverse.
Invasive plants can choke out native species, which are the bedrock of local food chains. This can degrade vital habitats and food sources and interrupt an ecosystem’s ability to adapt to change. The ripple effects are huge: they mess with water purification, carbon storage, and even climate regulation. Some species can bring in new pests and diseases that threaten ecosystems and crops, too.
Thanks to the horticultural trade, transportation, and climate change, invasive plants are only growing in number across Ontario. Sadly, there is no one-size-fits all approach to eradicating invasive species. Removal and management strategies will depend on how each species spreads. But importantly, when removing invasive species, put these plants in black garbage bags and leave them to bake in the sun for at least one week to kill the plants before putting them in your garbage bins for transport to the dump. DO NOT put these plants in compost or yard waste bags. We don’t want them spreading any more than they already have!
Next, we’ll dive into 25 common invasive plants in Ontario and some gorgeous, eco-friendly, and easy-to-grow native alternatives you can plant instead.
Common Invasive Plants in Ontario and What to Plant Instead
Perennials
Creeping Bellflower (Campanula rapunculoides)
Daylily (Hemerocallis fulva)
Purple Loosestrife (Lythrum salicaria)
Yellow Flag Iris (Iris pseudacorus)
Bulbs
Siberian Squill (Scilla siberica)
Trees and Shrubs
Buckthorn (Common, Sea and Glossy: Rhamnus cathartica, Hippophae rhamnoides, and Frangula alnus)
Burning Bush (Euonymus alatus)
False Spirea (Sorbaria sorbifolia)
Honeysuckles (Non-Native: Amur, European Fly, Japanese, Morrow, Showy, Tartarian)
Japanese Barberry (Berberis thunbergii)
Norway Maple (Acer platanoides)
Tree of Heaven (Ailanthus altissima)
Groundcovers
Creeping Bugleweed (Ajuga reptans)
Creeping Charlie (Glechoma hederacea)
Creeping Jenny (Lysimachia nummularia)
English Ivy (Hedera helix)
Goutweed (Aegopodium podagraria)
Lily of the Valley (Convallaria majalis)
Pachysandra (Pachysandra terminalis)
Periwinkle (Vinca minor)
Grasses
Miscanthus (Miscanthus sinensis and Miscanthus sacchariflorus)
Dishonourable Mentions
Coltsfoot (Tussilago farfara)
Dog-Strangling Vine (Vincetoxicum rossicum)
Garlic Mustard (Alliaria petiolata)
Japanese Knotwood (Reynoutria japonica)
Phragmites (Phragmites australis)
Groundcovers
Most invasive groundcovers thrive in partial to full shade, though many can spread in almost any light condition. Because of this, many of the native alternatives listed for one invasive species will also work for others. The alternatives I've selected for each plant are not only visually similar but also share similar growth habits, making them great substitutes.
Creeping Bugleweed (Ajuga reptans)
Creeping bugleweed is an invasive groundcover for part to full shade that is still sold in Ontario garden centres! It takes over quickly, spreading via stolons, and provides little value to native ecosystems.
It will grow back from any piece of root or stem left behind, so it must be thoroughly removed. Luckily, its roots are fairly shallow. Digging around the plant and clearing the soil will do the job.
Native Alternative - Wild Blue Phlox / Woodland Phlox (Phlox divaricata)
Wild blue phlox is a beautiful, low-growing (9-12 inches tall) perennial that blooms in April-May. It can form large colonies over time, with blooms that range from light blue to purple. It prefers part to full shade and average moisture, although it can be relatively drought tolerant once established. It does well in sandy or loamy soils.
Importantly, it supports ecosystem health by providing for local pollinators, specifically long-tongued bees, butterflies and moths. It is also a host plant for the Tiger Swallowtail Butterfly.
Native Alternative - Common Blue Violet (Viola sororia)
Common Blue Violet is a lovely spring-blooming groundcover and an important early nectar source for native pollinators. It also serves as a larval host plant for Fritillary butterflies and several moth species.
It can do well in all light conditions and all soil types (sand, clay, loam) with average soil moisture, making it very easy to grow. It is low-growing (under 1 foot) and can tolerate light foot traffic.
Creeping Charlie (Glechoma hederacea)
Creeping Charlie is a quick-spreading perennial that was introduced to North America from Europe through colonization. It spreads in two ways: by seed, and by stolons (or creeping stems). It loves shady spots but, much to the frustration of homeowners, can easily take over in sunnier areas too.
What makes Creeping Charlie extra sneaky? It’s allelopathic, meaning it releases chemicals that suppress neighboring plants, giving it an edge and making it even harder to control.
Native Alternative - Woodland Strawberry (Fragaria vesca)
Woodland Strawberry is a charming, low-growing perennial known for its small, sweet strawberries and delicate white flowers. It thrives in a variety of conditions but does best in partial shade to full sun and moist, well-drained, loamy soil. It will tolerate some drought once established. Its spring blooms attract pollinators like bees and butterflies. Plus, the fruits are a bonus treat for both wildlife and gardeners!
Creeping Jenny (Lysimachia nummularia)
Creeping Jenny is a fast-spreading evergreen groundcover with bright green or golden, rounded leaves and small yellow flowers that bloom in late spring to early summer.
It is shade tolerant, thriving in partial shade to full sun. While beautiful, it is highly invasive and often found in wild areas as it easily escapes home gardens.
Native Alternative - Partridgeberry (Mitchella repens)
Partridgeberry is an evergreen groundcover native to Ontario, prized for its glossy green leaves, delicate white summer flowers, and bright red berries that persist through winter.
Partridgeberry thrives in partial to full shade and prefers moist, well-drained soil, requiring minimal maintenance once established.
Its berries provide food for birds and small mammals, while its flowers attract native pollinators.
English Ivy (Hedera helix)
English Ivy is an evergreen vine that is highly invasive in Ontario, despite still being sold in garden centres! Known for its rapid, aggressive growth, it often escapes into wild areas and smothers native plants. English Ivy spreads by seeds and by growing long vines that take root at their joints and climb over anything in their way. It can grow horizontally as a groundcover, or vertically as a vine.
This plant thrives in partial to full shade and prefers moist, well-drained soil, but it is highly adaptable and can grow in a wide range of conditions.
Native Alternative - Virginia Creeper (Parthenocissus quinquefolia)
Virginia Creeper is a fast-growing, deciduous vine that’s well-known for its vibrant red foliage in the fall. Like English Ivy, it can serve as a groundcover or a vine. Unlike some invasive climbers, Virginia Creeper does not typically harm the trees it climbs and can be controlled with pruning.
This vine grows in a variety of light conditions, from full sun to shade, and adapts well to a variety of soil types. It is highly tolerant of urban environments and is a versatile choice for covering large areas quickly.
In addition to supporting local pollinators, its berries are an important food for birds and small mammals.
Native Alternative - Large-Leaved Aster (Eurybia macrophylla)
Large-Leaved Aster is a hardy, shade-tolerant perennial native to Ontario, known for its large, heart-shaped leaves and clusters of pale flowers that bloom in late summer to fall. It spreads by rhizomes and is an excellent groundcover for woodland gardens and shaded areas, where it can form dense colonies. Its flowers attract a variety of pollinators, including bees, butterflies, moths, and other beneficial insects, and its dense foliage offers shelter for small wildlife.
Goutweed (Aegopodium podagraria)
Goutweed is a highly invasive perennial that spreads aggressively through underground rhizomes. Its adaptability to all conditions make it popular as a groundcover, so it is sadly still sold in nurseries in Ontario! Once established, Goutweed is notoriously difficult to eradicate as every bit of root will produce a new plant.
Its rapid spread and versatility make it a significant threat to gardens, woodlands, and natural areas in Ontario, where it outcompetes native species and disrupts ecosystems.
Native Alternative - Virginia Waterleaf (Hydrophyllum virginianum)
Virginia Waterleaf is a native perennial that features attractive, lobed leaves and clusters of lavender or white flowers in late spring. Its flowers provide an early nectar source for bees and other pollinators. This plant spreads by rhizomes and is self-seeding, making it a great groundcover for woodland gardens and areas in partial to full shade.
Native Alternative - Canada Anemone (Anemone canadensis)
Canada Anemone is a hardy, adaptable native perennial that forms dense colonies with bright white flowers that bloom from late spring to early summer. It spreads through underground rhizomes, making it a vigorous groundcover.
Canada Anemone thrives in full sun to partial shade and prefers moist, well-drained soil, though it can tolerate wet conditions and poor drainage.
It plays an important role in supporting native pollinators and ecosystems. Its spreading habit helps stabilize soil, preventing erosion in wetter areas, while providing shelter and cover for small wildlife.
Lily of the Valley (Convallaria majalis)
Lily of the Valley is a fragrant, shade-tolerant perennial that is still sold in garden centres in Ontario! With bell-shaped white flowers and broad, glossy green leaves, it is prized for its beauty and scent, but is highly invasive in Ontario. This aggressive plant spreads through underground rhizomes, crowding out native plants. Once established, Lily of the Valley is difficult to control and can quickly take over gardens and natural areas. While it prefers partial to full shade, it can adapt to a variety of soil types and tolerate dry conditions. Do not purchase or plant this bully!
Native Alternative - Solomon’s Seal (Maianthemum stellatum)
Solomon’s Seal, also known as Starry Solomon’s Seal, is a graceful, shade-loving perennial native to Ontario. It features arching stems with lance-shaped leaves and delicate clusters of star-shaped white flowers in spring, followed by small, attractive berries in late summer. The plant spreads slowly via rhizomes. It tolerates a range of conditions, but thrives in
partial to full shade and in moist, well-drained soil. Solomon’s Seal supports biodiversity by providing nectar for bees and other pollinators, while its berries are a food source for birds and small mammals.
Pachysandra (Pachysandra terminalis)
Pachysandra, commonly known as Japanese Spurge, is a popular evergreen groundcover prized for its lush, glossy green leaves and small white flowers that bloom in early spring. It prefers partial to full shade, but can be adaptable. It rapidly spreads via rhizomes, creating thick mats that can overtake native plants. It can come back from even the tiniest root fragment, making it a headache to eliminate. Pachysandra frequently escapes into nearby forested areas, harming native ecosystems.
Native Alternative - Wild Ginger (Asarum canadense)
This evergreen groundcover thrives in shade or part shade and can thrive in all soil types (sand, clay, loam) in medium to moist conditions. In spring, it briefly produces dark red-purple flowers that are tucked beneath the leaves. Growing half a foot tall, its heart-shaped leaves make it an attractive groundcover that supports local ecosystems. It is also the larval host plant for the Pipevine Swallowtail butterfly.
Periwinkle (Vinca minor)
Periwinkle is a tough, evergreen groundcover prized for its shiny leaves and purple flowers in spring. While it adds beauty to gardens, it is invasive in Ontario and harms native ecosystems. Beware - it is still being sold in garden centres!
Periwinkle thrives in partial to full shade and adapts easily to various soil types. Its drought and shade tolerance make it popular for challenging garden spots. However, its aggressive growth poses a serious threat to biodiversity as it commonly escapes home gardens.
Native Alternative - Wild Geranium (Geranium maculatum)
Wild Geranium is known for its attractive, deeply lobed leaves and showy, pale pink to lavender flowers that bloom in late spring. This clump-forming plant slowly spreads by rhizomes to create a lush groundcover.
It thrives in partial shade to full sun and prefers moist, well-drained soil, though it can tolerate a range of conditions, including drier soils once established. It is a versatile and delightful choice that is beneficial for pollinators, attracting bees, butterflies, and other insects.
Perennials
Creeping Bellflower (Campanula rapunculoides)
Creeping bellflower is an especially difficult plant to deal with, as any seasoned gardener will tell you! Introduced from Europe, it spreads in two ways: through a creeping root system of rhizomes and by producing an abundance of seeds (up to 15,000 per plant). The rhizomes have a sneaky habit of spreading under fences, sidewalks, and even concrete! This resilient and determined plant can quickly become a persistent challenge in your garden.
Eradicating creeping bellflower will likely be a multi-year project. Creeping bellflower's root system is deep, consisting of long tubers that can easily detach from the upper roots. Any pieces of tubers left in the ground will produce more plants!
Native Alternative - Harebell (Campanula rotundifolia)
A delightful native alternative to Creeping Bellflower is Harebell. Harebell grows best in sandy or loamy soil, part shade to full sun, and in dry to medium soil conditions. It's purple bell-like flowers bloom from summer to fall. A lovely bonus: this plant is a favourite of hummingbirds!
Native Alternative - American Bellflower (Campanulastrum americanum)
American bellflower is a biennial that can grow up to 6.5 ft tall in either clay, sand, or loamy soil. It prefers sun to light shade and regular moisture (medium to moist conditions). It blooms between June and August, boasting blue star-shaped flowers. Note: It is only a true native to the very southern tip of Ontario.
Daylily (Hemerocallis fulva)
Daylilies are robust perennials known for their striking orange flowers. They are commonly called “ditch lilies” as they thrive in the ditches along roadsides. Though admired for their low-maintenance beauty, they spread readily through underground rhizomes and are highly invasive in Ontario. Daylilies thrive in a wide range of conditions, from full sun to partial shade, and tolerate various soil types. Their roots are dense and tuberous, crowding out other plants. Any small piece left in the ground can regenerate into another plant. Their adaptability and rapid spread make them a threat to natural habitats near human settlement.
Native Alternative - Michigan Lily (Lilium michiganense)
The Michigan Lily is one of the few dazzling lilies native to Ontario, lighting up gardens with its bright orange blooms and elegantly curled-back petals. Blooming in the height of summer, this lily thrives in moist, well-drained soils and full to partial sun. More than just a pretty face, Michigan Lily is a pollinator magnet, attracting hummingbirds, butterflies, and native bees.
Purple Loosestrife (Lythrum salicaria)
The deceptively pretty Purple Loosestrife is a highly invasive perennial plant in Ontario, recognizable by its tall spikes of vibrant purple-pink flowers. Native to Europe and Asia, it was introduced to North America in the 19th century and has since spread aggressively in wetlands, marshes, and along riverbanks and roadsides. It thrives in moist, nutrient-rich soils but can tolerate a variety of conditions, including full sun or partial shade. Its adaptability and prolific seed production (up to 2.7 million each year!) make it a serious ecological threat, particularly to wetlands.
Native Alternative - Blue Vervain (Verbena hastata)
Blue Vervain is a hardy native wildflower with tall spikes of tiny, vibrant blue-violet flowers. Growing from 2-5ft tall, it supports a wide range of native pollinators, including bees, butterflies, and hummingbirds. Blue Vervain is tough yet graceful, thriving in moist, rich soils and full to partial sun.
Native Alternatives - Blazing Stars (Liatris spicata, L. aspera, and L. cylindrica)
Ontario native Blazing Stars are some of my favourite perennials, including Liatris spicata, Liatris aspera, and Liatris cylindrica. Dense Blazing Star (Liatris spicata) is a stunner, with its tall, feathery spikes of bright purple flowers. Blooming in mid to late summer, it’s a favourite among native pollinators. Monarch butterflies and swallowtails are particularly drawn to its rich nectar, along with native bees and hummingbirds. Growing 2-5ft tall, it thrives in full sun and well-drained soils, often tolerating drought.
Native Alternative - Anise Hyssop (Agastache foeniculum)
Anise Hyssop is a fragrant, bee-friendly, near-native herb with tall spikes of lavender flowers. Blooming from mid-summer to early fall, its sweet licorice scent and abundant nectar make it irresistible to native pollinators. Bumblebees, mason bees, and leafcutter bees flock to its blooms. Its long-lasting flowers provide an extended food source for pollinators as other blooms fade at the end of the season. Anise Hyssop thrives in full sun to partial shade and well-drained soils.
Yellow Flag Iris (Iris pseudacorus)
Yellow Flag Iris is an attractive but highly invasive perennial in Ontario, recognized by its large, showy yellow flowers. Native to Europe, Asia, and North Africa, it thrives in wetland areas including marshes, riverbanks, and lakeshores. It spreads through both seeds and rhizomes, forming dense stands that displace native species and reduce habitat quality and food sources for wildlife. Thriving in full sun or partial shade, its ability to colonize wetlands is alarming. Ontario has already lost over 70% of its vital wetland ecosystems, which support at least 20% of species at risk in the province.
Native Alternative - Blue Flag Iris (Iris versicolor)
Blue Flag Iris is a striking native iris that brings splashes of deep blue and purple to Ontario’s wetlands and shorelines. Blooming in late spring to early summer, its elegant, vibrant blooms are a magnet for native pollinators, particularly native bees. It also provides shelter for small wetland wildlife and supports water-loving pollinators, such as certain hoverflies and dragonflies. It thrives in full to partial sun and consistently moist soils.
Native Alternative - Canada Lily (Lilium canadense)
Canada Lily boasts graceful, vibrant orange and yellow blooms in mid-summer. Its bell-shaped flowers dangle delicately from tall stems, attracting a range of native pollinators. Hummingbirds are particularly drawn to its bright, tubular flowers, which also attract swallowtail butterflies and bumblebees seeking nectar. It thrives in moist, well-drained soils and does well in partial shade to full sun.
Native Alternative - Cardinal Flower (Lobelia cardinalis)
Cardinal Flower is another striking native wildflower that prefers wet conditions. It lights up Ontario’s wetlands, stream banks, and moist meadows with its brilliant red blooms in late summer. It is a favourite of hummingbirds, which are among the few pollinators able to access its long, tubular flowers. Thriving in full to partial sun, Cardinal Flower is perfect for damp settings.
Bulbs
Siberian Squill (Scilla siberica)
Siberian Squill is an early-blooming favourite that, while admired for its delicate blue flowers, is invasive in Ontario. It can poisonous if eaten by some animals, including dogs. It spreads quickly through seeds and bulbs, forming dense colonies that outcompete native spring ephemerals like Trilliums and Bloodroot. This leads to a loss of biodiversity, reducing spring food sources and habitat for pollinators and other wildlife. Like most invasives, Siberian Squill is adaptable and can thrive in a variety of conditions, making it especially pernicious.
Native Alternative - Virginia Bluebells (Mertensia virginica)
Virginia Bluebells bring delicate shades of blue to Ontario gardens in early spring. Native bees are frequent visitors, along with the occasional butterfly seeking an early-season feast. Growing up to 2 feet tall, Virginia Bluebells thrive in moist, well-drained soils and partial to full shade. As one of the first spring blooms, they play a vital role in supporting pollinators emerging from winter and contribute to a healthy, biodiverse ecosystem.
Other early blooming blue beauties include Woodland Phlox and Common Blue Violet, mentioned above.
Grasses
Miscanthus (Miscanthus sinensis and Miscanthus sacchariflorus)
Miscanthus are tall (up to 6.5 feet), ornamental grasses native to Asia and Africa. These species spread vigorously through rhizomes and seeds, overtaking native plants and reducing biodiversity in our ecosystems. Miscanthus is particularly problematic in disturbed habitats, wetlands, and along roadsides. It thrives in full sun and well-drained soils, but is adaptable to a range of conditions, including poor or disturbed soils. Once established, it is difficult to remove.
Native Alternative - Indian Grass (Sorghastrum nutans)
Indian Grass is a tall (up to 8 feet), elegant native grass with striking golden-yellow inflorescences, especially in late summer and fall. This perennial grass thrives in full sun, adapting well to a variety of conditions, including drought. Its deep root system helps stabilize the soil and prevent erosion. Indian Grass provides essential habitat and food for numerous wildlife species, including birds like the Eastern Meadowlark and American Goldfinch, which feed on its seeds. It also supports native pollinators.
Other tall native alternatives include Switch Grass (Panicum virgatum) and Big Bluestem (Andropogon gerardii).
Trees and Shrubs
Buckthorn (Common, Sea and Glossy: Rhamnus cathartica, Hippophae rhamnoides, and Frangula alnus)
Common Buckthorn, Sea Buckthorn, and Glossy Buckthorn are all part of the same family, the Rhamnaceae family. This plant family is commonly known as the buckthorn family and includes various shrubs and small trees, many of which are known for their invasive tendencies. Beware: Glossy Buckthorn is still sold in Ontario! Sea Buckthorn is often prized by gardeners for its berries, but is also invasive in Ontario.
Native Alternative - Chokeberry (Aronia melanocarpa)
Chokeberry is a versatile native shrub that adds beauty and ecological value. It sports clusters of delicate white flowers in spring and glossy black berries in late summer. This resilient plant thrives in various conditions, from full sun to partial shade, and is adaptable to most soil types. Chokeberry not only provides a vital food source for birds and small mammals, but it also attracts a variety of pollinators, including bees and butterflies, during its flowering period.
Native Alternative - Nannyberry (Viburnum lentago)
Nannyberry is a lovely native shrub with creamy white flowers in spring and clusters of dark blue-black berries in the fall. Thriving in full sun to partial shade, this adaptable plant prefers well-drained soils but can tolerate a range of conditions, including wet sites. Nannyberry serves as an important food source for various wildlife, including birds like cardinals and bluebirds, while its fragrant flowers attract pollinators, including bees and butterflies.
Native Alternative - Serviceberry (Amelanchier Canadensis)
Serviceberry is a delightful native tree or shrub that flaunts stunning white flowers in early spring and sweet, juicy berries in early summer. This versatile plant is a favorite among wildlife, providing an essential food source for mammals and birds, including robins and bluebirds. Its blooms provide for a range of pollinators, making it a valuable asset for local biodiversity. With its multi-season interest, from beautiful blooms to vibrant fall foliage, Serviceberry enhances the aesthetic appeal of landscapes while promoting ecological health.
Burning Bush (Euonymus alatus)
Burning Bush is known for its brilliant red foliage in the fall, which has made it a popular ornamental plant. However, it is highly invasive in Ontario, easily escaping home gardens by producing copious amounts of seeds. Once it takes root, Burning Bush forms dense thickets that outcompete native plants, reducing biodiversity and altering natural habitats. This shrub thrives in full sun to partial shade and can tolerate a range of soils, including dry and disturbed areas, making it highly adaptable and difficult to control. It can form monocultures that dominate forests, fields, and roadsides.
Native Alternative - Eastern Wahoo (Euonymus atropurpureus)
Eastern Wahoo is a gorgeous native shrub in the same family as Burning Bush. It too boasts fall interest, showing off with vibrant pinkish-red fruits that burst open to reveal bright orange seeds, providing a feast for birds like robins and cardinals. Its small, purplish flowers in spring attract native bees and other pollinators, supporting biodiversity early in the season. Thriving in partial shade and moist soils, Eastern Wahoo adds beauty to woodlands and hedgerows while enhancing habitat quality.
False Spirea (Sorbaria sorbifolia)
False Spirea is a fast-growing, deciduous shrub with attractive, fern-like foliage and fluffy white flower clusters in mid-summer. Although appealing, it is highly invasive, spreading through underground rhizomes and quickly forming dense thickets that disrupt natural ecosystems. This shrub thrives in full sun to partial shade and tolerates a range of soils. Its adaptability and relentless production of suckers make it incredibly difficult to control.
Native Alternative - Meadowsweet (Spirea alba)
Meadowsweet is a lovely native shrub that brings a touch of elegance to Ontario’s wetlands, meadows, and stream banks. In midsummer, it produces clusters of delicate, fluffy white flowers that are a magnet for bees, butterflies, and other pollinators. Its dense foliage and fibrous roots also help stabilize soil, preventing erosion along waterways. Preferring full sun and moist to wet soils, it is a beautiful and functional addition to your garden.
Image from Nature in the City of Toronto
Honeysuckles (Non-Native: Amur, European Fly, Japanese, Morrow, Showy, Tartarian)
These non-native honeysuckles, originally from Asia and Europe, grow rapidly with prolific reproduction. They take over natural areas, crowding out native plants and disrupting ecosystems. Reaching from 6.5 to 16 feet tall, their summer blooms range from white to pink to crimson. Invasive honeysuckles take over the understory, blocking forest regeneration and reducing wildlife habitat. Japanese and Tartarian honeysuckles are still sold in Ontario. Do not plant these invasive shrubs!
Native Alternative - Bush Honeysuckle (Diervilla lonicera)
Bush Honeysuckle is a hardy native shrub with yellow, trumpet-shaped flowers blooming in early summer. It attracts a variety of pollinators, including bees, butterflies, and hummingbirds. This shrub thrives in full sun to partial shade and adapts well to dry and/or rocky soils. As a native honeysuckle, it forms low, dense thickets that provide shelter and nesting sites for small wildlife, making it a clear winner over its invasive counterparts!
Japanese Barberry (Berberis thunbergii)
Japanese Barberry is an ornamental shrub that has become highly invasive in Ontario and other parts of North America. It spreads aggressively through its abundant seeds, which are dispersed by birds. Japanese Barberry thrives in full sun to partial shade and is highly adaptable, tolerating a wide range of soil types. Its striking fall foliage and vibrant red berries that last through winter make it a favourite of gardeners looking for all-season interest. But, sadly, it poses a serious threat to natural habitats, and herbivores will not eat it due to its sharp thorns.
Native Alternative - Winterberry (Ilex verticillata)
Winterberry is a native deciduous holly that adds year-round appeal to Ontario gardens. Known for its bright red berries that persist through the colder months, Winterberry provides an important food source for birds when other food is scarce. In summer, its small white flowers attract pollinators, and its glossy green leaves turn yellow in the fall. It thrives in most soils that are medium to moist and in full sun to partial shade.
Ninebark (Physocarpus opulifolius) and Snowberry (Symphoricarpos albus) also boast berries that can last through the winter, although Snowberry spreads quickly and may overwhelm small gardens.
Norway Maple (Acer platanoides)
The Norway Maple is an invasive tree from Europe that is often grown in urban areas since it can tolerate pollution, foot traffic, and salt. While popular as a shade tree, it produces a large number of seeds that spread easily and its dense canopy shades out understory plants, reducing biodiversity. It is also allelopathic and produces chemicals that slow down the growth of nearby plants, and local wildlife do not eat it or its seedlings. If you or your neighbours have one, you are likely well aware of how many saplings it produces each year!
Native Alternatives - Sugar (Acer saccharum), Freeman (Acer x freemanii), and Silver (Acer saccharinum) Maples
All of these native maples are well-suited to Ontario’s climate and offer valuable benefits to wildlife. Each native maple serves as a host plant for hundreds of native butterfly and moth species. In urban spaces, Freeman or Silver maples are appropriate choices, as they can tolerate pollution. Sugar maples can not, and thus tend to thrive in more rural areas.
Hackberry (Celtis occidentalis) trees are also great choices for urban spaces as they can tolerate pollution and support native butterflies and birds.
Tree of Heaven (Ailanthus altissima)
Tree of Heaven is an aggressive, non-native tree that has become a major environmental threat in Ontario. Originally from China, it spreads rapidly through both seeds and suckers. Known for its ability to thrive in poor soils and urban environments, Tree of Heaven also releases allelopathic chemicals that inhibit the growth of other plants. It is also the preferred host of the invasive spotted lanternfly, highlighting how the spread of non-native plants can exacerbate the spread of invasive pests, creating a damaging cycle for local ecosystems.
Native Alternative - Staghorn Sumac (Rhus typhina)
Staghorn Sumac is a native Tree of Heaven look-alike that provides ecological value rather than diminishing it. Known for its striking, velvety branches, it produces vibrant clusters of red berries in late summer and fall, which provide food for birds including robins and cedar waxwings. Staghorn Sumac is a hardy, drought-tolerant plant that thrives in full sun to partial shade and can adapt to a variety of soil types, including dry, rocky, and disturbed areas.
Dishonourable Mentions
These common invasive plants are not typically planted or cultivated purposely, particularly since Dog Strangling Vine, Japanese Knotweed and Phragmites are on Ontario’s Restricted Species List, making them illegal to import, deposit, release, breed/grow, buy, sell, lease or trade. Dog Strangling Vine and Coltsfoot are also on Ontario’s Noxious Weed List, and thus homeowners are legally required to remove them. Here is information on how to remove these plants if you find them on your property.
Coltsfoot (Tussilago farfara)
Coltsfoot is an aggressive, invasive perennial plant that spreads rapidly in Ontario. It was brought to North America from Europe during colonization as it was prized as an herbal medicine. Known for its early yellow flowers that appear before the leaves, it establishes itself in disturbed areas like roadsides, ditches, and riverbanks. Sadly, I often find this noxious weed along trails in public parks and protected areas. Coltsfoot spreads both by seeds and by an extensive underground rhizome system, allowing it to quickly form dense patches that crowd out native plants.
To control or eradicate Coltsfoot, it’s important to dig out the entire plant, including its deep and spreading root system, as any remaining rhizome fragments can regenerate. Cut back the flowers before they go to seed. For larger infestations, repeated cutting throughout the growing season can weaken the plant. Another method would be to cover the area in thick black plastic and leave it until the rhizomes are starved from lack of water and photosynthesis. However, this method, while less labour intensive, can harm soil health. As with other invasive species, consistent monitoring and follow-up efforts are essential to prevent regrowth and keep it from re-establishing.
Dog-Strangling Vine (Vincetoxicum rossicum)
Dog-Strangling Vine is a highly invasive perennial vine. Originating from Europe, it spreads through both wind-dispersed seeds and underground roots, forming dense, smothering mats that outcompete native plants. Its rapid growth and ability to thrive in a variety of conditions, including forests, meadows, and disturbed areas, allow it to take over quickly. Dog-Strangling Vine can also interfere with the life cycle of native butterflies, as Monarchs may mistakenly lay eggs on it, but the larvae cannot survive.
To control or eradicate small patches of Dog-Strangling Vine, dig out the plant thoroughly, ensuring that all roots are removed, as even small fragments can regrow. For larger infestations, repeated cutting can weaken the vine, but herbicide application directly to the leaves or cut stems is often needed for effective control. Monitor the area to determine if repeated treatments are necessary.
Garlic Mustard (Alliaria petiolata)
Garlic Mustard is an invasive herb native to Europe that has become a serious threat to Ontario’s woodlands and natural areas. It spreads rapidly by seed, forming dense colonies and altering soil composition, limiting the growth of other vegetation. Garlic mustard thrives in shaded, moist areas and can easily colonize forest floors.
To remove garlic mustard, it’s best to pull or dig up the plants, making sure to remove the entire root to prevent regrowth. This should be done before the plants flower and set seeds, ideally in early spring. Dispose of pulled plants in a sealed bag, as leaving them in the area can lead to further seed dispersal. Regular monitoring and removal over several years are essential to effectively control this invasive species.
Japanese Knotweed (Reynoutria japonica)
Japanese Knotweed is a highly invasive species that is difficult to control without herbicide. Originally from East Asia, it spreads rapidly through underground rhizomes. Japanese Knotweed thrives in a variety of environments and, like many invasives, it alters soil composition and prevents the regeneration of native vegetation.
Digging up the extensive root system is difficult and even small fragments can lead to regrowth. For this reason, targeted herbicide applications are often most effective, especially in more established infestations. This is one of the few plants I’d recommend using Glyphosate to eradicate. Ensure you are wearing protective gear and use a brush to carefully paint the herbicide on the leaves and into cut stems.
Phragmites (Phragmites australis subsp. australis)
The invasive Phragmites Australis poses a significant threat to Ontario’s wetlands and aquatic ecosystems. You have likely seen this grass lining the ditches of Ontario’s highways and roadsides! Native to Europe, it spreads aggressively through both seeds and underground rhizomes. It forms monocultures that outcompete native vegetation, degrade wildlife habitat, and reduce biodiversity. Phragmites thrives in wet, marshy areas and can rapidly dominate shorelines, reducing water flow, and altering water quality.
There is a subspecies of Phragmites (Phragmites australis subsp. americanus) native to Ontario that does not tend to form dense monocultures, and is losing ground to the invasive subspecies. Here is more information on how to distinguish between the native and invasive phragmites: https://www.opwg.ca/phragmites/native-vs-invasive/
To remove the invasive strain, it is essential to target both the above-ground growth and the extensive root system. In dense areas, the most effective method will likely involve using a systemic herbicide applied to the cut stems. Yes, this is one instance where herbicide (glyphosate-based or imazapyr-based) can be warranted. Invasive control programs often include a combination of mechanical removal, herbicide treatments, and restoration of native vegetation. Two stem-boring moths have also been enlisted in the fight against Phragmites. Monitoring and follow-up treatments are necessary to prevent regrowth and ensure long-term control.
For a full list of Ontario’s invasive species, see: https://www.returnofthenative.ca/native-species/70-not
