Japanese Knotweed – Fallopia japonica

Synonyms: Reynoutria japonica, Polygonum cuspidatum 

What is it?

Also known as Mexican bamboo, Fleeceflower, Japanese Polygonum or Huzhang, and many other names, the Japanese Knotweed is a shrub-like semi-woody perennial plant native to East Asia known for its resilience, and attractive bamboo-like stems with large broad leaves and clusters of flowers. 

Photo of Japanese Knotweed by W.carter, CC0, via Wikimedia Commons

First introduced to North America in the 1800s, with the first recorded sighting in 1901 in Niagara Falls, Ontario, the Japanese Knotweed was initially planted as an ornamental species and to control erosion. It has since spread throughout the eastern seaboard, particularly in Ontario where it is most established in the southern and central areas, and as far as Newfoundland, especially in open woods, floodplains, and forest edges. Some specimens were found in British Columbia, though limited records made tracking its spread difficult. Likewise, little public attention has been paid to this alien plant except in the last two decades. 

As an ornamental plant, grown for its aesthetic qualities, the Japanese Knotweed mostly grows in gardens, and is a less prominent invasive species than most others. Outside of your backyard, and your grandmother’s garden, the Japanese Knotweed is mostly found in two types of environments: along stream banks, where it grows best in the wetland conditions, and in highly disturbed and derelict sites, such as along roadsides, railroads, ditches, and near old or former building sites, especially in abandoned material like soil, and aggregates etc.

Once established, Japanese Knotweed is known for being incredibly persistent and difficult to remove, with at least one dense cluster in Toronto surviving multiple repeated attempts at pruning, digging, and herbicide uses over years. This is achieved by their aggressive, highly dense and vigorous root systems. Notably, unlike many other invasive species, the Japanese Knotweed has difficulty making inroads in Undisturbed forested areas. Additionally, the Japanese Knotweed is vulnerable to persistent freezing conditions, and our harsh Canadian winters have ensured that the Japanese Knotweed is not as common as you might think. Nevertheless, the warming climate may soon change this. 

Why you should care

Like the Norway maple, the Japanese Knotweed has only recently been recognized as an invasive species. Due to its aggressive and lively root system, which can grow as far as 10m in every direction from the parent system, it can grow through concrete and asphalt, damaging urban infrastructure, building foundations, and increasing maintenance costs. This root system is so aggressive and persistent that it can survive even severe floods, and disasters! 

Japanese Knotweed
Japanese Knotweed growing through concrete. Photo by Kerry Wixted via Flickr.

In fact, one way Japanese Knotweed can spread without human intervention is during floods; pieces of the root system can break off in a flood, and start a new population where it lands. Ironically, despite being planted to prevent erosion by many settlers, the plant is not as good as many native plants at preventing erosion, and typically makes stream banks where it is common less stable, and more vulnerable to erosion and flooding in heavy storms. Near such waterways, thickets of Japanese Knotweed can also impede access, preventing recreational activities like canoeing, boating, angling, and swimming on affected riverbanks and shorelines.   

Japanese Knotweed along a stream bank. Original photo found here.

Outside of the gardens it is mostly found in, the Japanese Knotweed can very quickly and aggressively grow into dense thickets preventing 90% of sunlight from reaching the forest floor, enabling it to outcompete and suppress the growth of native plants. The Japanese Knotweed can grow as quickly as 8 cm per day, or 1m in three weeks. There is a reason why it is often compared to bamboo. Wildlife, including insects, rarely feed on the plant, so its rapid growth can quickly reduce native biodiversity and food supplies for local amphibian, reptile, bird, and mammal populations, effectively degrading the entire ecosystem. Additionally, the Japanese Knotweed is suspected of releasing chemical compounds that can alter soil chemistry and/ or inhibit the growth of other plants. Worst of all, even when they (eventually) die, its thick layers of decomposing plant matter can continue to suppress native plant growth for years.    

What can we do?

Given its reputation for near immortality, do not despair dear readers, there is much we can and should do about Japanese knotweed! Although it is almost indestructible, with at least one case of volunteers still battling an infestation as of 2017, and beginning in 2010, this monstrous hydra of plant CAN and will be brought to heel through perseverance and hard work. 

Or you know, just don’t plant it in the first place. 

Unlike a lot of other invasive plants, there is still room for us to prevent widespread colonization by Japanese knotweed, and it is always easier to remove newer plants than established thickets. If you live by a waterway, and you’re in the market for an erosion resisting plant, try native plants that are way better than Japanese knotweed like these:

  • Field pussytoes
  • Silverweed
  • Virginia waterleaf
  • Barren strawberry
  • And many more!

Otherwise, if you can, volunteer with efforts to help remove it where it can be found because they’ll need all the help they can get. When doing so, or going on a walk through locations known to be infested by this immortal alien hydra, stay on designated trails, avoid walking through thickets of Japanese knotweed, and always check your clothing and equipment for fragments or seeds that might have broken off can be carried away and spread. Never buy or plant Japanese knotweed, and never compost it as even the smallest root fragments and seeds can grow into new thickets. Instead, bring them to your local composting facility which can monitor the process while meeting provincial regulated temperature requirements.   

However, in order to help out, you’ll first need to know how to identify Japanese knotweed! 

 How to identify Japanese Knotweed

  • Height
    • Can grow 1 – 5 m in height
  • Stem
    • Dense clusters of tall straight bamboo-stems that may bend over under its own weight when extremely tall
    • Each stem can be between 2.5 – 3 cm thick 
    • Stems are hollow-jointed with reddish brown solid nodes with a papery sheath
    • Younger stems are green with purple splotches, resembling asparagus
    • Older stems can be reddish brown 
    • In winter, they appear as bare, grey, or straw colored hollow stalks  
    • New stems can emerge in late March to early April from an overwintering root system that can grow as far as 10 m away underground from the surface plant. 
  • Leaves
    • Oval heart to triangular shaped with a pointed tip
    • 8 – 10 cm wide and 10 – 17 cm in length 
    • Grows in alternating patterns from purple-red stems branching off of the main stem 
    • Green, but may have purple blotches on the edges and veins 
  • Flowers
    • Blossoms in the spring and up to July or August 
    • Found only at the end of the stems resembling wheat stalks
    • Attractive clusters of small white or green flowers growing along the tip of the stems in plumes 
  • Fruit
    • Produces fleshless winged oval shaped seeds that point into the stem 
    • Shiny beige or off white papery sheath covers the darker seed 

Can you remove Japanese Knotweed? 

But of course! Some would even go so far as to say there is a kill on sight order on these. However, be prepared dear reader to be in it for the long haul, perhaps years or even decades at worst, should you attempt to tackle these hydras of plants, for they have a reputation for immortality for a reason! As always, the best protection is prevention and avoid planting it in your backyard. 

If you do happen to find these bamboo like menaces in your garden, some of the best control methods include:

  • cutting off the flower heads to prevent seed production 
  • cutting off stems and applying herbicides to the roots and cut stems – best done in summer and fall 
  • digging up the entire root system 
  • smothering – best done in spring

However, using one of these methods is not usually helpful; the more combinations and techniques you use to fight this hydra of a plant, the more successful you might be. Most importantly, never give up, no matter how long it takes. Other methods and techniques can be found here:

If you see any plants that match the description above, please contact the Invading Species Hotline at 1-800-563-7711 or the Natural Resources Information Support Centre at 1-800-667-1940 or 1-800-387-7011 to submit your observations! Also consider visiting the EDDMapS Ontario which has partnered with both organizations above to report sightings!

Interested in learning more? See also:


Purple Loosestrife – Lythrum Salicaria

What is it?

If there is any invasive species Canadians may want to keep, it is the purple loosestrife. One of the more beautiful invasive species, the purple loosestrife is appropriately named for the colourful plumes of pinkish-purple flowers blooming throughout summer. While eye-catching, the purple loosestrife is not just a pretty bloom; it was once widely regarded as one of the most aggressive and pesky invasive species threatening wetlands across North America!  

Purple loosestrife at Rockwood Conservation Area. Photo taken by Mandy Huynh.

Native to Eurasia, the purple loosestrife is an herbaceous flowering wetland plant first introduced to eastern North America in the early 19th century. While some were planted in gardens for their showy blooms, others were brought over to help in beekeeping, due to the many blossoms, providing an abundance of nectar. Even more grew spontaneously around harbors and rivers due to sailors dumping ballast soil dug up in Europe and carrying the small seeds of the purple loosestrife. Like other hardy invasive species, it spread rapidly throughout North America and by 1992, became such a threat that it is one of the few invasive species which the Canadian government authorized the use of the controversial technique of biological control (releasing non-native species) to manage these flowers – releasing European leaf-eating beetles – the natural predator of the purple loosestrife into the environment to try to slow its spread. 

Galerucella calmariensis (a Leaf beetle) 1
Galerucella calmariensis, an European leaf-eating beetle species released to manage population of purple loosestrife. Photo taken by Jonathan, available on Flickr.

Although the release of these beetles reduced purple loosestrife populations by 90% in Ontario, it can still be found almost everywhere in North America, save for Florida, Alaska, and Hawaii. Purple loosestrife is especially common throughout the Great Lakes-St. Lawrence region where it can usually be found growing in wetlands, floodplains, and damp roadsides. 

Why you should care

Prior to the release of these beetles, rampant overgrowth by this deceptively pretty plant clogged our wetlands and waterways. Due to its aggressive and rapid growth, growing up to 30 flowering stems per plant, per year. Each of which produces millions of seeds every year that spreads easily by water, wind, and wildlife and stay dormant for decades before sprouting. It also regenerates from the smallest root fragments, allowing the purple loosestrife to overtake almost any shoreline and riverine habitat in Ontario. 

Once established, its dense thickets choke out other plants, while its thick roots make accessing waterways difficult and increase costs to keep riverways, and irrigation and drainage ditches clear of purple loosestrife. Most insidiously, this deceptively magenta bloom greatly degrades soil quality. Its dense growth strips vital nutrients, interrupt river flows, and alter downstream lakes, increasing the occurrence of scummy algal blooms; a real trickle-down effect. Native plants that are most at risk because of purple loosestrife in Canada include: 

  • The dense blazing star (Liatris spicata)
  • Eastern prairie fringed orchid (Platanthera leucophaea)
  • False hop sedge (Carex lupuliformis)
  • Swamp Rose-mallow (Hibiscus moscheutos)

The loss of these native plants reduces the amount of habitat, good foraging material, and shelter available to all wildlife, further degrading an infested wetland. Especially at risk are the spotted turtle (Clemmys guttata), and spiny softshell turtle (Apalone spinifera). Even beavers, critical to wetland ecosystem health, find purple loosestrife detestable. Perhaps the only good purple loosestrife brings is that at least the bees still find their nectar good! Were it not for leaf eating beetles like Galerucella calmariensis and G. pusilla, purple loosestrife populations would be even more rampant!

However, all of this is standard for most invasive species. Why then, does the purple loosestrife receive special attention?

As everyone knows, British Columbia, California, and most recently, Europe are all burning. With the looming threat of climate change, carbon sequestration has never been more important, and one of the most important carbon sinks in Ontario are our wetlands. 

Purple loosestrife in a wetland. Photo by Liz West, available on Flickr.

Although purple loosestrife is a fast-growing and expansive plant, it also damages and endangers the health of our wetland ecosystems, altering their hydrology and reducing their overall carbon sequestration efficiency. It may no longer be as common as it once was, and our wetlands are bouncing back with conservation efforts, but if we are to commit to fighting climate change, management of purple loosestrife and curtailing its impacts are just one of many ways we can all help. 

What can we do?

The case of the purple loosestrife in Canada is one of the few stories of successful invasive species management. The tightly regulated release of leaf eating beetles for the purpose of controlling the growth of purple loosestrife led to the purple loosestrife now viewed almost as just another Canadian wildflower. 

The best way to help is to not plant any; after all, purple loosestrife was originally and sometimes still planted for its attractive flowers. Its pinkish purple blooms can be confused for other garden plants and native wildflowers such as:

  • fireweed (Epilobium agustifolium), 
  • blue vervain (Verbena hastata
  • blazing stars (Liatris spp.)
  • winged loosestrife (Lythrum alatum
  • swamp loosestrife (Decodon verticillatus)

Follow the description below to see if you’ve got any purple loosestrife stealthing about in your backyard!

How to identify Purple Loosestrife

  • Height
    • Can grow between 1.5 – 3m tall 
  • Stem
    • Woody square stiff stems with hair
    • Each plant can produce between 30 – 50 erect stems
    • Each stem or root, when fragmented can grow into new plants
  • Leaves
    • in opposite pairs or whorls of three
    • lance-shaped leaves 3 -12 cm long 
    • normally green but can turn scarlet red in autumn
  • Flowers
    • Found at the top of the stems in dense footlong spikes of showy pinkish-purple blooms
    • Each flower has 5 – 7 petals, 10 millimetres long and small yellow centres 
    • Bloom from May to June
  • Fruit
    • 3–6-millimetre long and 2mm wide capsule resembling a dried brown umbrella or cup containing dozens to a hundred tiny 1-millimetre seeds 
    • Each seed resembles a tiny, reddish-brown wrinkled almond 

To prevent accidentally spreading fragments, always make sure watercraft are cleaned before and after use, and dried for at least 21 days before changing water bodies. Also, never dump water or soils that may hold purple loosestrife seeds from one location to another, and dispose of any fragments in the trash.   

Can you remove Purple Loosestrife?

Purple loosestrife is very well known to many conservation managers. Over the past 60 years, the best methods for controlling purple loosestrife have been determined and optimized to the point that purple loosestrife in the wild is no longer considered to need regular removals, and is carefully balanced with the beetles used to control it. 

As always, feel free to remove any purple loosestrife on your own property from which it could spread, with the younger the infestation, the easier it will be to manage it. However, you’re in for the long haul; this zombie plant can take years to clean up.  

You can remove whole stands, root and all, by hand for individual plants, but try shovels and weed pullers for larger plants. Never mow down purple loosestrife; the fragments will be like zombies growing back, and always remove any purple loosestrife that has been dug up to be dried for at least a week before disposal via burning. However, removing purple loosestrife always runs the risk of releasing fragments and seeds, so be sure to plan your removals during and before the summer, when the flowers are still blooming. Also check with your local municipality to see if they have any special instructions for disposal or composting programs for purple loosestrife! 

Because purple loosestrife tends to grow near the water, it is inadvisable to use fire or herbicides to control any stands. Fire will be ineffective due to the wet soils, while herbicides could poison downstream habitats. Also do not try flooding purple loosestrife; you will only spread it more.

If you see any plants that match the purple loosestrife, please contact the Invading Species Hotline at 1-800-563-7711 or the Natural Resources Information Support Centre at 1-800-667-1940 or 1-800-387-7011 to submit your observations! Also consider visiting the EDDMapS Ontario which has partnered with both organizations above to report sightings!

Interested in learning more? See also:


Garlic Mustard – Alliaria petiolata 

What is it? 

Garlic mustard, sometimes called hedge garlic, poor man’s mustard, garlic root, and many other names, is an invasive biennial herb native to Europe. As expected from its name, all parts of this plant give off a distinctive garlic scent. It was introduced to North America during the 1800s as a culinary herb due to its availability in early spring, high nutrient value, particularly in vitamins A & C, and was sometimes planted to control erosion as well. It was used as a medicinal herb for disinfecting wounds, or as a diuretic. While no longer popular, its seeds and chopped leaves can be used as a flavouring for salads and sauces. It has since escaped into the wild and can be found in southeastern Ontario, and parts of Quebec, with smaller populations in British Columbia, Nova Scotia, Prince Edward Island, and New Brunswick. 

Why you should care

Garlic mustard is one of the most aggressive invasive species in Ontario, due to its ability to double the size of its stands every four years and needing only half that to mature. Following their first wintering, surviving garlic mustard stands can produce thousands of seeds per square metre to be spread by people and animals (but not by wind!) that can still grow even 30 years after dispersal. 

Like many other invasive species, garlic mustard can grow in a wide range of habitats, including riverbanks, roadsides, and forest clearings, both sunny and shaded, disturbed and undisturbed. Its ability to grow earlier in the season allows it to outcompete many other native plants through their ability to release chemicals that hinder competitors. garlic mustard can aggressively overtake any available space and soil nutrients leaving little to no room for native plants. Worst of all, despite its nutritious leaves, garlic mustard is rarely a good food source for native fauna and is poisonous to some species like butterflies. As a result, even when removed, it leaves behind a nutritionally starved landscape unable to support salamanders, ground nesting birds, and other small herbivores.   

Unless quickly removed, garlic mustard can take over an ecosystem within 5 – 7 years and weaken its ability to resist other invasive species. This ability to undo decades of conservation work in only a handful of years is what makes it so threatening to the Canadian landscape. Here in Ontario, our famed trilliums are especially at risk because of the spread of garlic mustard, including the drooping trillium (Trillium flexipes). Other wildflowers and plants that are at risk include the eastern false rue-anemone (Enemion biternatum), hoary mountain mint (Pycnanthemum incanum), trout lily (Erythronium americanum), white wood aster (Eurybia divaricate), wild hyacinth (Camassia scilloides), wood poppy (Stylophorum diphyllum), and american ginseng (Panax quinquefolius).  

What can we do?

Although garlic mustard is not a significant source of food to local wildlife, it is also not poisonous or dangerous in any way for humans to handle and can and should be removed wherever you can find it before it spreads too far. 

Those with hobbies in foraging can try their hand at including it in some way in their cuisine if they’re brave enough! However, never consume weeds from public parks without washing to avoid accidentally consuming herbicides. Additionally, avoid young garlic mustard plants, and either cook thoroughly or chop them up to reduce the chances of food poisoning. 

Of course, to help fight back against garlic mustard, readers will first need to know what garlic mustard looks like right?

How to identify Garlic Mustard

Although garlic mustard can be easily identified up close by the garlic smell it releases when any parts are crushed, it can also appear very similar to many other native plants at a distance, like carrots, daisies, violets, and mustards, especially when not in bloom. Before removing any plants that seem like garlic mustard, check for these characteristics to be sure you are really removing garlic mustard.

Alliaria petiolata - Garlic Mustard
Garlic Mustard 2nd year growth.
  • Height
    • First year plants can be herb like plants less than 0.3 meters high
    • Mature second year plants can be up to 1.3 meters high
  • Stem
    • First year plants look almost like a small bush, with each purplish green stem bearing a leaf, arranged in a basal rosette 
    • Mature second year plants have non-wooded hairy stiff stems emerging from a white taproot smelling of horseradish
  • Leaves
    • First year plants have one small (2 – 3 cm) dark green, deep veined leaf per stem, each a circular kidney shape with rounded scalloped teeth, with dozens arranged in a bush like rosette 
    • Second year plants have large (3 – 8 cm) triangular deep veined leaves with jagged teeth arranged in an alternative pattern around the central stem 
    • When crushed, a strong garlic smell is released 
  • Flowers
    • Appear only at the top of the stem in small clusters of multiple cross-shaped white flowers, 
    • Bloom in May to early June for second year plants  
  • Fruit
    • By mid summer, second year plants can have barren looking branched stems at the top – these are seed pods, 2.5 – 6 cm long, each carrying 10 – 20 small black seeds 

Can you remove Garlic Mustard? 

Absolutely! Many local conservancies, including the Nature Conservancy of Canada (NCC) often host volunteer programs to help remove local infestations of garlic mustard on public land so try applying to your local conservancy to participate on family friendly garlic mustard removal expeditions. Stay on designated trails to avoid picking up stray seeds, and clean clothing and shoes to prevent spreading more garlic mustard. 

Of course, readers are welcome to remove any they find on their own property. Due to its resilient roots, it can be difficult to remove garlic mustard, so infestations have to be found and treated early for easy management. Some environmentally safe techniques include:

  • Hand Pulling – most effective in April/May, or September/October, however this can also stimulate the growth or release of seeds. Make sure you’ve pulled up the s-shaped root to prevent resprouting of plants, repeat until the infestation is gone, and follow up with replanting native species in their place
  • Mowing/clipping – most effective in early May with second year plants that flowered but have yet to produce seeds. Like hand pulling, mowing or clipping may need to be repeated especially if the root is not removed.
  • Disposal
    • Once your garlic mustard crop has been obtained, if you do not intend to consume them, you have to dispose of them safely. Never compost garlic mustard, and always seal your harvest in waste bags tightly in direct sunlight. Flowered plants can still produce seeds, so they should either be dried or burned. 

Consider other ways to prevent garlic mustard from growing in your backyard. Avoid planting garlic mustard and other invasive plants, and buy native plants from reputable suppliers. Always stay on the lookout for this outlaw of a plant!  

If you see any plants that look like the garlic mustard, please contact the Invading Species Hotline at 1-800-563-7711 or the Natural Resources Information Support Centre at 1-800-667-1940 or 1-800-387-7011 to submit your observations! Also consider visiting the EDDMapS Ontario which has partnered with both organizations above to report sightings!

Interested in learning more? See also:

Norway Maple – Acer platanoides

What is it?

The Norway maple is an invasive deciduous tree native to Eurasia, the hardwood of which is commonly used in furniture and other products. Music lovers may be interested to know it may have been one of the woods used to produce the famous Stradivari violins!

Jonathan Billinger / A fine Norway Maple, Acer platanoides

First introduced to North America in the mid-1700s as an ornamental tree, the Norway maple’s popularity exploded following the second world war after American elms (Ulmus americana), the then predominant ornamental native tree, largely disappeared due to disease. It remains favoured among gardeners and horticulturists to this day. Norway maples can be found from coast to coast across Canada, from British Columbia, through Ontario, and Newfoundland in the east, and as far north as the Yukon.

Distribution of Norway Maple in the Greater Toronto Area.
EDDMapS. 2022. Early Detection & Distribution Mapping System. The University of Georgia – Center for Invasive Species and Ecosystem Health. Available online at http://www.eddmaps.org/; last accessed July 13, 2022.

Chances are, readers of our blog have sat under the shade of these trees at least once in their lives, in the park, or by the sidewalk. The most noticeable feature of these alien Maples are their five lobed leaves, with many different cultivars famous for their rich colours: vibrant green, and purple in the summer, that become a rich red or yellow in autumn.

However, on closer inspection, you’ll find that the Norway maple is nowhere near as pleasant as our native Sugar maple (Acer saccharum). Instead of a sugary sap, when broken, the stems of the leaves of Norway maples release a white sap and the toothy leaves are more sinisterly jagged. Lastly, the most noticeable evidence of a Norway maple is its helicopter blade like seeds, called samaras, which fall in summer to coat your driveway. Yes, those oddly shaped seeds belong to them [the Norway Maple].

Norway Maple Samaras.
Homer Edward Price, CC BY 2.0, via Wikimedia Commons

Why you should care

Due to its horticultural popularity, the Norway maple is rarely recognized as an invasive species; many even celebrate the autumn colours they bring to local parks. Nevertheless, they are gaining notoriety for damaging local infrastructure and increasing cleanup costs in municipalities. Being fast growers, these trees need much more regular pruning than other trees. Additionally, their brittle branches can easily snap in storms, leaving countless debris.

Worse, these trees are everywhere. Due to its popularity. for the last century, Norway maples have been planted in most cities across Ontario as an ornamental tree. Although its main means of spreading in North America is through human action, Norway maples can easily invade surrounding enclaves of native plants, by releasing its winged seeds, called samaras, that can be carried far by the wind and germinate quickly making it one of the few invasive species that can make inroads against the established forest canopy. This, along with its ubiquity has allowed other invasive flora and fauna to overrun reserves of native species making the Norway maple especially threatening.

The primary means by which the Norway maple damages Canadian forests is by outcompeting native species, usually through its higher tolerance to poor growing conditions. For example, it can survive in polluted urban areas and has a longer growing season. Additionally, at least one study found native sugar maples invaded by Norway maples were more vulnerable to insect and fungal damage, suggesting Norway maples can outlast their native competitors. There is even some evidence their leaves and roots may release toxins to kill off competitors. Once planted, their seedlings can grow into dense mats, draining the soils of water. As they continue to grow, an expanding shallow root system and thick canopy can choke out competing native species such as sugar maples, and other plants.

What can we do?

Unlike many invasive species, Norway maples is an established species across North America. Therefore, unlike other invasive species, merely keeping an eye out for them won’t be much help, except when identifying newer infestations as it is always easier to remove new seedlings rather than established trees. Instead, efforts should be made to replace this alien with native trees and plants. However, to do so, it is crucial to recognize and eventually remove them. Indeed, some native maples such as the red maple (Acer rubrum) can look very similar to the more colourful non-native varieties of Norway maple, so be careful!  

How to identify Norway maples

Although similar to many other native maple trees such as sugar maple, Norway maples can be distinguished by subtle differences on closer inspection. Consider these characteristics to help you figure out if what you’re looking at is a Norway maple…

  • Height
    • Norway maples can grow up to 20-30 m tall before ending in a round crown
  • Trunk
    • As a deciduous hardwood, Norway maples are covered in a grey-brown bark lined by criss-crossing grooves
  • Leaves
    • Like other deciduous trees, Norway maples first turn yellow or red in autumn, before losing their leaves in winter, eventually sprouting new blunt rounded buds in the spring
    • The leaves have the distinct five lobed shape unique to maples with fine hairs at the tip of each lobe
      • Each lobe has 2 – 3 jagged points but otherwise has a smooth edge
    • The leaves grow in opposing pairs, each 10 – 18 cm wide, and 8 – 16 cm long     
    • When damaged at the stems, a milky white sap may leak   
    • Depending on the species, the leaves can be maroon (ex. Crimson King), purple (ex. Schwedleri), or green.
  • Flowers
    • From April to May, Norway maples can produce large umbel-clusters of small (~8-10mm) greenish-yellow flowers, each with five petals
  • Fruit
    • Although Norway maples do not produce fleshy fruit, each of the thousands of female flowers can play host to a pair of paper-like winged seeds called samaras
    • These samaras also have larger and broader angled wing blades compared to native maple seeds 

Can you remove Norway maple?

It is highly recommended that, if possible, any and all Norway maples on your property should be removed in favor of a native tree or plant. Saplings can be manually dug out, while larger trees must be cut down, preferably when seeds are not present.

Please note many municipalities require an application/tree removal permit prior to the removal of larger trees. Be sure to check the bylaws of your local government prior to any removal!

More developed trees are tougher to remove, requiring peeling back the bark with 4-inch-wide cuts in the spring and early summer to weaken it before cutting. Even leftover stumps cannot be allowed to persist as new growth can develop from these hardy maples. While powerful chemical herbicides can be used, always contact experts and consult with product labels while remaining within provincial and federal laws, and it is likely that several years of control will be required to completely remove Norway maple in this manner, with such herbicides most effective on seedlings or young saplings.

As always however, the easiest method of impeding the spread of this alien maple is early detection, whether that is on your property or at any gardening centre still selling Norway maple saplings. Seedlings are easiest to remove when young, and in wet soils. As Norway maples are most often spread by intentional planting of this attractive plant, you can refrain from buying and planting it. Don’t be fooled! Norway maple can be sold under differing trade names such as ‘Crimson King, ‘Emerald Queen’, ‘Schwedleri’ and many more.

Instead, plant native trees and plants. Excellent native trees that are similar in appearance to the attractive Norway maple include the Manitoba maple (Acer negundo), red maple (Acer rubrum), silver maple (A. saccharinum), and their hybrid Freeman’s maple (Acer freemanii), as well as the sugar maple (A. saccharum). The Freeman’s maples may be found under trade names like ‘Celebration’, ‘Autumn blaze’, and ‘Scarlet sentinel’.

Other alternatives include hackberry and serviceberry, both of are just as hardy and tolerant of urban conditions, with the latter even providing fruit!

Interested in learning more? See also:

European buckthorn – Rhamnus carthartica

What is it?

The European buckthorn, common buckthorn, or just buckthorn, is an invasive flowering tree native to Europe that was introduced in the 1880s to Canada, and has since spread across the country, becoming widespread throughout eastern Canada by the 1900s. They remain common across Ontario, having been naturalized in many regions and are one of the most iconic invasive plant species.  

Unlike our previous plant guest, buckthorn is well named for the sharp thorns at the end of its branches hidden by its lush green foliage. Since the leaves of this prickly tree species tend to stay a little longer than its native colleagues in the forest, they can stick out to hikers planning to enjoy a colourful autumn at this time of year. Watch out though, though their thorns aren’t poisonous, they’re certainly not dull!

Why you should care

Common Buckthorn (Rhamnus cathartica), not to be confused with the similarly named but native Alder Buckthorn (Rhamnus alnifolia), is one of the most iconic and harmful invasive species, and it isn’t just because they can poke your eye out if you fall into one by accident!

Much like other naturalized invasive species, the common buckthorn and its relatives like the Glossy Buckthorn (Frangula alnus) were often deliberately planted and spread by humans to serve as ornamental plants, hedgerows and windbreakers. Additionally, its berries, which are mildly toxic to humans, are sometimes consumed by birds and small mammals that then disperse the seeds that pass through their intestinal tracts and can be spread over a wide area to quickly germinate.

Combined with its hardy nature, being able to repeatedly resprout from just its roots, and tolerance of a very wide range of soils and low light conditions, the common buckthorn can thrive in many environments. As a result, it has become extremely common in Ontario, and can be found along roadsides, fences, the edges of urban forests, and other locales. 

Beyond being the occasional nuisance, the spread of the invasive common buckthorn has had serious negative effects on the landscape. Not only does this prickly bush take up space that could have otherwise housed native trees and shrubs, but its dense thickets, which develop leaves before and last long after most native plants, can crowd and shade out new undergrowth, including important wildflowers and herbs, and even alters soil nutrients to discourage potential native competitors while favoring other invasive species like garlic mustard. This has also diminished local water quality as many native plant species are critical to reducing erosion and runoff. 

Additionally, though buckthorn berries are often consumed by small wildlife, it has little nutritional benefit, has laxative properties, and is toxic in high quantities, being eaten only because, like our prickly enemy’s leaves, they persist even into winter, being a seemingly easy source of food for unsuspecting mammals and small birds. 

Worse, this nasty invader has also had an impact on Canadian agricultural output! The common buckthorn can serve as hosts for at least three agricultural pests. One is the Oat Crown rust (Puccinia coronate spp. avenae), which appropriately harms oat crops (Avena sativa). Another is the spotted wing drosophila (Drosophila suzukii), a fruit fly pest that has damaged many soft fruit and berry crops that Ontario is famous for. The third, and more dangerous pest that the common buckthorn invites is the soybean aphid (Aphis glycines). This nasty critter not only hurts soybeans, but other vegetable crops as well, by consuming them and using them as host plants to survive the winter. Even worse, the soybean aphid itself has facilitated the invasion of the multi-coloured Asian Lady Beetle (Harmonia axyridis) which feed on the aphid and whose presence has led to the decline of native lady beetle species.  

As a result, there should be no surprise that the common buckthorn listed as a noxious weed in Ontario’s Weed Control Act, with growing awareness and efforts in recent decades to stamp it out and restore our native ecosystems!

What can we do?

The best way to help reduce the impacts of the common buckthorn is to help identify and report infestations. Much like other invasive species, early detection is critical in controlling its spread as younger shrubs are much more easily removed compared to older growths.

How to identify Buckthorn

The common buckthorn is one of the more distinctive invasive plants out here in Ontario but can sometimes be confused with the similar glossy buckthorn, which is also invasive, and should also be removed, so in this case, mix-ups between the two are no great loss, though this is unlikely to happen as while the common buckthorn prefers well-drained soils, the glossy buckthorn prefers to grow in wetlands. 

However, you should not confuse either for the native alder buckthorn, though it is more similar in appearance to the glossy buckthorn than the common buckthorn. 

To identify a true common buckthorn, look out for the following characteristics:

  • Height
    • Depending on the site, the common buckthorn can grow as a short shrub two to three metres tall, but under optimal conditions, can grow into a tall six-metre tree.  
  • Stem
    • Woody twigs with sharp thorns at the tip rather than on the sides like a rosebush
    • At its full size at 6 metres, the central trunk can be up to 25 centimetres in diameter
    • Younger shrubs will consist of multiple stems with flakey bark 
  • Leaves
    • Glossy dark green on top, and pale green on the bottom; retains its colour even in late autumn when it becomes more obvious   
    • Short stalk per leaf
    • Opposite, with fine toothed margins, and parallel veins curving into the tip 
    • Leaves generally elliptical ranging from two-point-five to six centimetres long, rounder at the base, and narrowing into a curved pointed tip. 
    • Develop early in the spring, and only loses its leaves in late autumn, sometimes persisting into early winter 
  • Flowers
    • Small, inconspicuous with two – six light yellow-green petals 
    • Flowers during May and June
  • Fruit
    • Distinctive clusters or singular stalked glossy purplish-black round (5 – 6 mm) berries
    • Juicy with stony seeds that can germinate quickly
    • Develop during in July and August, but can persist into the winter despite shriveling 

Can you remove Buckthorn?

If it is on your property, instances of common and glossy buckthorn can and should be removed and replaced with native species like these.

As we stated earlier, because buckthorn shrubs are easiest to remove when young, monitor your property for any emergent saplings. Like other invasive species, any instances of common buckthorn shrubs should be removed in their entirety, from root to stem. This can be accomplished by manually pulling up the buckthorn saplings and is easiest in mid-October when the common buckthorn is not only easiest to identify by its distinctive persistent leaf cover, but when the soils are loose and damp, and collateral effects on other species will be minimal. Stronger tools such as weed wrenches may be used to clamp onto the stems of buckthorn saplings and pull them out. 

When removing the pulled-up buckthorn plants, do not discard them in the compost, or deposit them in natural areas as they are extremely hardy, and may resprout roots, or overlooked seeds in the flowers may germinate, allowing the infestation to persist. 

However, if the stand is too well developed, pruning can be used to slowly cut back the extent of the infestation, until the plant either dies or can be more easily removed. Legal herbicides may also be used, either separately or in conjunction with pruning efforts. 

In any case, the hardiness and extent of common buckthorn infestations in Ontario are generally so serious that you should be prepared to spend several years battling recurring and persistent infestations. While it can be tempting to use limited burning practices, as many city officials and conservation authorities sometimes do, we DO NOT recommend attempting this as it can quickly become a serious fire hazard. 

A more detailed set of management practices for controlling and removing common buckthorn infestations can be found below:

On public properties, many conservation authorities organize expeditions to collect and remove emergent saplings. Check with your local conservation authority to see if you can participate!  

Additionally, you can also help prevent the spread of invasive plants like the common buckthorn by staying on trails and keeping pets leashed, reducing the chances that your clothing or pet’s fur will pick up and spread its berries and seeds. 

If you see any plants that match the description above, please contact the Invading Species Hotline at 1-800-563-7711 or the Natural Resources Information Support Centre at 1-800-667-1940 or 1-800-387-7011 to submit your observations! Also consider visiting the EDDMapS Ontario which has partnered with both organizations above to report sightings!

Additionally, importation of the common buckthorn and other invasive plants is illegal and can be reported to the MNRF TIPS line at 1-877-TIPS-MNR (847-7667) toll-free anytime. You can also call Crime Stoppers anonymously at 1-800-222-TIPS (8477).

Interested in learning more? See also:

Ontario’s Invading Species Awareness Program – Common Buckthorn (Rhamnus cathartica)
Ontario Weeds: European Buckthorn 
Nottawasaga Valley Conservation Authority – Common & Glossy Buckthorn
Ontario.ca – Common Buckthorn
Friends of the Mississippi River – Buckthorn: How can a shrub be so harmful?
Grow Me Instead
Invasive Common (European) Buckthorn (Rhamnus cathartica) – Best Management Practices in Ontario

Dog Strangling Vine – Cynanchum rossicum  (formerly Vincetoxicum rossicum) 

What is it? 

Dog strangling vine, also known as European swallowwort, pale swallowwort or just swallowwort is a perennial non-woody flowering plant, native to southeastern Europe and Asia, and introduced to North America in the 1800s for gardening but which has since become invasive. 

Contrary to its menacing name, this vine like plant cannot strangle man’s best friend but its rapid spread across southern Ontario and parts of the US, makes it a threat to local biodiversity. 

Why you should care 

Dog strangling vine can quickly grow and settle in new areas with tough, thick roots via seeds carried by the wind. Once established, the dog-strangling vine can easily regrow from even small fragments of its root system making it difficult to remove from infestations.  

Although it prefers open sunny areas, dog strangling vine is also common in areas disturbed by humans such as old fields, railways, and a broad variety of urban environments, and will aggressively wrap around native plants and trees to form dense mats of vegetation in the underbrush, literally ‘strangling’ their access to sunlight and suppressing other plants from growing.   

The result is a reduction in habitat and food available to birds and larger animals. Dog strangling vine also poses a threat to insects, being avoided by pollinators, and is often mistaken for native milkweeds by the already endangered monarch butterfly. Since the monarch butterfly needs to lay its eggs on native milkweed plants for its larvae to survive, by being tricked into leaving its eggs on a look-alike, the spread of dog strangling vine could further reduce the population of these beloved butterflies.   

What can we do? 

Early detection is key! – if we can remove instances of dog strangling vine before they become too well established, dog strangling vines can be much more easily managed! 

How to identify dog strangling vine 

dog-strangling vine | As lovely as it is invasive. I've neve… | Flickr
Photo by Steve Begin @flickr (CC)

Dog strangling vine can be confused for many other plants, including the black dog strangling vine (Vincetoxicum nigrum), which is within the same genus and visually similar but has darker coloured flowers.  

It may also be confused for native milkweeds like common milkweed (Asclepias syriaca) which can be distinguished by its warty seeds, butterfly milkweed which has orange flowers and alternate leaves, and swamp milkweed. However, note that all native milkweeds are erect plants that do not twine like true dog-strangling vine.  

Similarly, dog strangling vine may also be confused for dogbane (Apocynum cannabinum), but which has erect reddish stems, droopy leaves, and white flowers.  

 To identify a true specimen of dog strangling vine, look out for these characteristics:


  • Dog strangling vine can grow up to heights of about 0.6 – 2m  


  • Herbaceous (non-woody) – will twine around surrounding objects, climbing around trees, and even among themselves to form dense vegetated mats  


  • Green, opposite, smooth, and wavey margins, ovoid with a pointed tip  
  • Leaves are rounder at the base, largest (7 – 12cm) at the middle of the vine, and smaller (5 – 7cm) and narrower at the top  


  • Pointed ovoid buds with twisted petals pre-blooming 
  • Occur at the vine tips  
  • 5 – 7mm individually  
  • Five-fold symmetry  
  • Usually red-brown, maroon, or pink though the undersides may be a lighter pink, orange, or yellow 
  • Blooms in late June and July 
  • Emerge in stalked clusters of 5 – 20 flowers with  


  • long pointed chili- like seed pod – 4 – 7cm long and 0.5cm wide 
  • contain milky sap 
  • green when un-ripened   
  • pale brown when ripe – will split open to release multiple fluffy seeds with coma (tufts of feathery hair) – seeds are easily distributed by wind contributing to their invasive status  

Can you remove dog strangling vine? 

Yes! Just like any other plant, if it is found on your property in small quantities, dog strangling vine plants can be physically pruned away to reduce its reproductive potential and ability to spread, but only digging it up or killing it, roots and all, will permanently remove plants already present. When digging it up, avoid tilling the soil excessively to prevent fragmenting and spreading the dog strangling vine’s roots.    

Please see the Landowner’s Guide to Controlling Invasive Woodland Plants or the Toronto Botanical Garden’s guide for more detailed instructions on how to physically remove instances of dog strangling vine, as well as other guides here.  

Chemical control via pesticides can also be effective on a larger scale but different herbicides can have different levels of effectiveness and more often just allows for other non-native species to move in. While you can buy the right pesticides from licensed vendors (see here for further details), it may be better to check with your local conservancy for volunteers they may need to help out! 

After any attempts at removing dog strangling vine, remember to check your clothing, any pets you may have, vehicles, and other equipment to ensure that you are not inadvertently spreading the seeds of this invader. Dispose of the remains in the garbage rather than the compost or in natural areas as discarded flowers may contain seeds.  

If you have removed any dog strangling vine on your property, consider planting native flowers in their place, which are just as beautiful and much more helpful to the local ecosystem.  

If you see any plants that match the description above, please contact the Invading Species Hotline at 1-800-563-7711 or the Natural Resources Information Support Centre at 1-800-667-1940 or 1-800-387-7011 to report your sighting! Also consider visiting the EDDMapS Ontario which has partnered with both of the organizations above to submit observations! 

Additionally, importation of dog strangling vines and other invasive plants is illegal and can be reported to the MNRF TIPS line at 1-877-TIPS-MNR (847-7667) toll-free anytime. You can also call Crime Stoppers anonymously at 1-800-222-TIPS (8477). 

Interested in learning more? See also: