Biodiversity Invasive Species Weeds

2023 February Weeds

The formal definition of a weed is any plant growing where you don’t want it. For gardeners struggling to eradicate weeds, it can seem like they have super powers. Well, maybe they do…

Whether from nature or a child’s puff, dandelion seeds are sensitive to wind direction, which helps them to disperse widely. Jon Feingersh Photography Inc./The Image Bank/Getty

Why dandelion seeds are so good at spreading widely

On any given dandelion, some seeds are destined to go north, while others are fated to fly east, south or west, and every direction in between. In effect, each dandelion seed is programmed to release for a wind coming from one direction and resists winds from other directions, according to research presented at the American Physical Society’s Division of Fluid Dynamics. Dandelion seeds are susceptible to different wind directions depending on where they are on the seed head, says Jena Shields, a biophysicist at Cornell University. The feathery seeds on the side facing a breeze will let go most easily; the others hold on tens to hundreds of times tighter — until the wind shifts. Shields measured the force it takes to pluck dandelion seeds by supergluing a fine wire to the tufted ends and pulling them from the seed heads at various angles. This seed-by-seed study mimicked what happens when wind, or a child’s breath, pushes them over. Because each seed is most susceptible to winds from distinct directions, it helps prevent seeds from all going the same way, Shields says, and may explain why the plants are so successful at spreading. Once blown off a dandelion, the umbrella-like tuft on a seed carries it on the breeze that pulled it away. In fact, it turns out the movement of air around dandelion seeds is teaching us a new way of moving through air, which also helps the seeds stay aloft much longer than would otherwise be the case!

Why we should all learn to love stinging nettles

Stinging nettles are food for peacock butterfly caterpillars. Keith Hider/Shutterstock

I still remember the itch and burn of stinging nettles (Urtica dioica) encountered while exploring wasteland areas as a child. We always used to rub the stinged skin with dock leaves (Rumex obtusifolius) to relieve the pain. Although there is no scientific evidence this actually works, it always made me feel better. Aside from their sting, which is their defense against being eaten, nettles offer a host of benefits. Permaculturalists love them because their fibrous roots, which make them such a pain to remove as weeds, help draw nutrients up from the subsoil and make them available to other plants. They are amazing at colonizing disturbed areas and bare soil – a useful trait at a time when human activity has disturbed so much nature. In addition to those persistent roots, Charles Darwin was right when he theorized that nettle seeds could withstand a long soak in salty water. This ability may have allowed the humble nettle to become a world traveller, colonizing areas across oceans. Those same seeds can lie dormant in soil for up to five years. Nettles are good for wildlife. They are larval host plants for Question Mark, Milbert’s Tortoiseshell, Red Admiral butterflies

Ouch! The silica hairs (trichomes) act as needles, injecting irritants into skin. Floki/Shutterstock

In the UK, nettles spreading to gardens and cultivated areas have allowed several species of butterflies to expand their range. Ladybugs often lay their eggs on nettles, and when those eggs hatch, the ladybug larvae are voracious eaters of aphids – one of the more persistent garden pests. Nettles are good food for humans, too. They are highly nutritious, full of vitamin A and C along with calcium and iron. Nettles have a long history in folk medicine and there is scientific evidence that extracts from nettle leaves, roots and stems can treat high blood pressure and diabetes.

Nettle fibers were used in Europe when the two world wars caused shortages. Indeed, there is evidence that people in cool climates have used nettles since the Bronze Age to create textile fibres until sheep breeding gave rise to more effective wool-producing sheep. So this is another “weed” with potential super powers.

Dog-strangling vine in Kanata (Photo credits to Green Ottawa)

Study explores control options for black swallowwort

Otherwise known as dog-strangling vine (Vincetoxicum nigrum), this nasty invasive plant has super powers that include rapid spread through wind-dispersed seeds and the ability to outcompete and strangle native species, including small trees. It also fools monarch butterflies into laying their eggs on it, but the monarch larvae can’t eat this nasty weed, so they starve.

I haven’t seen any information about potential beneficial properties and to date, no scientific studies have been conducted to determine how the weed responds to common controls, such as mowing and broad-spectrum herbicides. However, an article featured in Invasive Plant Science and Management, begins to fill this information gap. Over three years, the team explored how black swallowwort responded to two glyphosate products and one triclopyr product. The weeds were either sprayed annually with a two percent solution of one the herbicides at flowering in early July—or were mowed in early July and then treated in late August. The study showed the two glyphosate formulations were effective in reducing aboveground black swallowwort biomass, but they were less effective in reducing cover and stem densities. Researchers also determined that mowing failed to enhance the efficacy of the glyphosate applications on a consistent basis. With or without moving, Triclopyr was generally ineffective.

Biodiversity Citizen Science Climate Change Conservation Invasive Species

Happy Lunar New Year!

Photo by Pixabay on Pexels.

Today marks the Lunar New Year and the start of the year of the rabbit. While most gardeners are not fond of rabbits, Dr. Emma Sherratt, Evolutionary Biologist at The University of Adelaide, writes movingly of the plight of the once common bunny and its less common relatives.

In Australia, bunnies are a much-reviled invasive species that causes enormous ecological harm. Elsewhere, these long-eared animals fill diverse ecological niches. The long-eared animals we tend to call bunnies and the lesser-known pikas (small mountain-dwelling animals from Asia and North America) form a group of animals known as Lagomorpha. Science currently recognizes about 108 lagomorph species. These evolutionary cousins to rodents are found on all continents except Antarctica and are surprisingly close to primates on the Tree of Life. In 2013, researchers found that more than two-thirds of rabbit species were already threatened by climate change. Since then, the number of species that are endangered or critically endangered has risen from 13 to 16 on the International Union for Conservation of Nature Red List. The rabbits need our help.

Water Rabbits

Water rabbits are not just an astrological fancy. The swamp rabbit (Sylvilagus aquaticus) and marsh rabbit (S. palustris) of North America are adapted to living in wetlands and are known to swim. Luckily these species are marked as least concern on the conservation IUCN Red List. Less luckily, the riverine rabbit (Bunolagus monticularis), a majestic, reddish-coloured rabbit from South Africa that inhabits the banks of rivers and streams is critically endangered. This species faces both the effects of climate change and habitat destruction, and threats from other bunnies. Lepus hares, which are larger and are generalist feeders, out-compete and displace the riverine rabbits when resources become scarce.

Not all rabbits make endless babies

On two subtropical islands in southwestern Japan live Amami rabbits (Pentalagus furnessi), sometimes referred to as a “living fossil” because they have primitive characters like small ears and legs better for scurrying than hopping. The almost black Amami rabbits inhabit dense tropical forests, and are sadly endangered. Unusual among lagomorphs, Amami rabbits usually have only one – rarely two – offspring. That evolutionary adaptation worked well on for an island habitat where there were not predators. However, in 1979, Indian mongooses were introduced to combat snakes. The mongooses also ate a lot of bunnies. Authorities are now working on a mongoose eradication program to save the endemic rabbits and birds from extinction.

Mountain refuges

In times of climate change, mountains can become islands for alpine species. In the Annamite Range mountains of Vietnam and Laos lives another endemic rabbit (Nesolagus timminsi), striped in black and reddish-brown. This endangered species is among the least understood rabbits, but we do know it’s under threat from intensive poaching. In the mountains of Mexico lives the volcano rabbit (Romerolgaus diazi). One of the world’s smallest rabbit species, it is in trouble due to the effects of cattle grazing and land conversion for agriculture.

The tiny and adorable volcano rabbit is endemic to a handful of volcanoes in Mexico. Saúl Saldaña/iNaturalist, CC BY-NC

Even the European rabbit (Oryctolagus cuniculus), the only species to have been domesticated, is endangered in its native range, despite having been exported around the world by hungry humans who used them for food. In the Iberian Peninsula, where they are native, the European rabbit’s numbers have plummeted. Conservation measures are required because these bunnies are a key food source for  the Iberian lynx, which is making its comeback from being the most endangered cat in the world.

Protecting biodiversity

Many of the endangered lagomorph species have unique traits that are still to be uncovered by scientists. Limited geographical distributions and habitat preferences make them vulnerable to a changing environment and difficult to study. That is why citizen science is valuable for these species, because local eyes keenly spotting animals is one of the best methods for data collection. So make your Lunar New Year’s resolution to be a bunny advocate.

For example, you can go to the iNaturalist network to familiarise yourself with the diversity of species. And next time you’re on holiday and you see a rabbit, be sure to snap a picture and upload your sighting. In Canada, the Canadian Wildlife Federation offers information and tips on managing bunnies in your garden, and on indigenous species, such as snowshoe hares.

Invasive Species Miscellany

2023 January Seed News

Schematic by Maria Thereza Alves showing the components and sources of ballast.

Seeds of Change: New York – A Botany of Colonization

Thanks to Rebecca McMakin for highlighting a wonderful art exhibit by Maria Thereza Alves. The installation of Installation water paintings, texts, linen paintings and potted plants was inspired by a simple historical fact. Over 400 species of plants, mostly European in origin, were growing on ballast grounds throughout New York and New Jersey, from where they have spread further since. Ships arriving with ballast over the last few centuries were responsible for introducing much non-native flora to the East Coast of the U.S. So much so that botanist Viktor Muhlenbach writes, “Combing ballast grounds […] for the appearance of new plants was a popular botanical pastime of the late nineteenth and early twentieth centuries.” Earth, stones, sand, wood, bricks, and whatever else was economically expedient was used as ballast to stabilize merchant sailing ships in relationship to the weight of the cargo. Upon arrival in port, the ballast was unloaded, carrying with it seeds native to the area where the ballast had been picked up. Seeds of Change unearths historical ballast sites and ballast flora. It is an ongoing investigation of ballast flora in numerous port cities. Projects have been developed for Marseille, Reposaari, Dunkirk, Exeter, Liverpool, Bristol, and now New York. This fascinating art project is at once a look at the history of colonization and an attempt to decolonize.

Stock image by Mike on Pexels.

Row 7 Seeds

Row 7 is a US-based seed company that says it is “dedicated to deliciousness”. Based on collaboration between chefs, farmers and plant breeders, they are grounded in the notion that deliciousness might just change the world. The Row 7 team believes flavor can succeed where commodification has failed and that it can change how we eat and, in turn, how we grow. They explain that too many plant breeders select for appearance, shelf-life, yield  or uniformity – none of which qualities confer better taste on the result. Ten years ago—almost by accident—chef Dan Barber challenged vegetable breeder Michael Mazourek to build a better butternut squash. For Michael, it launched a new conversation around breeding for flavor. For Dan, it was the discovery of a new kind of recipe—one that begins with the seed. All their seeds were bred conventionally, so there are no GMOs. They also partner with regional organic farmers to support biodiversity above and below ground. The end goal? Unique vegetables grown for place, picked (and eaten) at the perfect moment. Currently, their veggies are only available through Whole Foods Market stores in the greater Boston area, but the company plans to expand. I’m sure gardeners are wondering if and when they might be able to purchase seeds!

Seedy Saturdays are coming! Wherever you live in Canada, keep an eye on the Seeds of Diversity website for information about your local Seedy Saturday event. Here in Ottawa, we will be able to enjoy two events. The traditional Seedy Saturday will take place at Ron Kolbus Lakeside Centre on Saturday, March 4. A west end event is being added that will take place the following Saturday. More details to follow.

Invasive Species

Spotted Lanternfly

Image credit: Lawrence Barringer, Penn DA,

Our friends at the Garden Professor’s Blog have a great profile on this attractive-looking but dangerous new invasive pest. As of late November 2022, the spotted lanternfly (SLF) was in upper New York State, a mere 5 km from the Canadian border. Consequently, it is another nasty invasive species that is likely to enter Ontario in 2023 and will probably make its way to Ottawa soon after.

Abi Saeed, the Extension Horticulture Specialist at Montana State University, writes that the SLF (Lycorma delicatula) is a 1″ (2.5 cm) long planthopper native to China. It has since spread to Japan, South Korea, and the United States. This piercing/sucking insect feeds on the phloem of plants and excretes a sweet and sticky product called honeydew. SLF feeding damage, especially in large populations, can impact the health of certain plant species. Not to mention the nuisance potential, as any objects under infestations of this insect will find themselves coated in a sticky layer of honeydew.

Pennsylvania Department of Agriculture , Licensed under a Creative Commons Attribution 3.0 License.

In the USA, the SLF was first detected in Pennsylvania in 2014, and has since moved to several surrounding states including Delaware, Indiana, Maryland, Massachusetts, Michigan, New Jersey, New York, North Carolina, Ohio, Rhode Island, Virginia, and West Virginia. Most US states are considered at risk for SLF invasion. Although the insect itself can’t fly long distances, it can be easily spread by moving infested materials and through their egg masses which look fairly nondescript (like a small smear of mud).

The Pennsylvania Department of Agriculture website also has some excellent information about the SLF. Among the preferred food sources of the SLF are plants that are economically important, including grapevines, maples, black walnut, birch and willow. A 2019 economic impact study estimates that, uncontrolled, this insect could cost Pennsylvania $324 million annually and more than 2,800 jobs.

Among the things we gardeners can do to help halt the spread of this invasive pest:

  • Learn to recognize the bug in its various life phases.
  • Destroy egg masses if you see them.
  • Don’t move woody material that might be infected.
  • In Canada, report any sightings the Invasive Species Centre by calling 705-541-5790 or emailing

How telephone poles could help stop the spotted lanternfly

John Rost, a research technologist at Penn State Berks, explains the spotted lanternfly research that is being conducted at the Penn State Berks Center for the Agricultural Sciences and a Sustainable Environment (CASSE). Credit: Samantha Bower / Penn State.

The Penn State Berks Center for the Agricultural Sciences and a Sustainable Environment (CASSE) is studying the role that telephone poles can play in monitoring and eradicating the invasive spotted lanternfly. Spotted lanternflies are drawn to tall objects like skyscrapers, gas pumps, pillars and trees, according to John Rost, a research technologist in the horticulture department at Penn State Berks. The lanternflies use these perches to gain their bearings before searching for a place to feed. At the CASSE, telephone poles were used as monitoring devices to test methods of eradication. In the study, eight poles were set up in a straight line to keep a replication. Two types of traps were installed on each pole: a top trap with a sealed barrier except for an opening at the bottom and a section of pole wrapped with pesticide impregnated netting which the insects encountered on their journey to the top. At the bottom of the pole there is a catch trap to collect any dead, falling lanternflies. The article includes notes on the challenges of identifying patterns in behaviour of the spotted lanternfly, as well as details of the insect’s life-cycle.

Invasive Species


Woman stripped Ontario river full of pesky invasive plant — by hand: Katie Church has yanked so many patches of the pesky invasive European water chestnut this summer, she has dreams about doing it. “I look at the chestnut in the water and [dream of] removing it and making sure everything is clear,” she laughs.

Church has just finished leading a field team of five summer students hired by the non-profit Invasive Species Centre. The group was tasked with searching, finding and plucking the thick, rooted green invasive aquatic plant by hand along a 30-kilometre stretch of the Welland River, in Ontario’s Niagara Region.

[Editor’s note: This article includes a 1:30 minute video explaining the term “invasive species”.]