Identify and prevent the spread of harmful plant species

Linaria dalmatica, or Dalmatian Toadflax was brought from Eurasia into North America in the late 19th century as an ornamental plant. The plant has become a problem species as one single plant can produce as many as 400,000 seeds in one year. As a result it is found in eight Canadian provinces (AB, BC, MB, NB, NS, ON, QC, SK) and almost all western states of the US. Dalmatian toadflax drastically reduce grazing land for livestock and wildlife as it contains toxic compounds which are harmful when consumed in large quantities, which is easy to do given how effectively it spreads. Mature plants compete against native species, overtaking large areas and converting them into giant weed plots. Scenarios similar to this one are still occurring even today, with many well known aggressive species still on the market today, being sold in nurseries or distributed among gardeners. Education is a powerful tool in combating invasive, and potentially invasive species, and it is our responsibility to prevent situations similar to the Dalmation toadflax outbreak before they get out of hand.

Understand Invasive Plant Impacts

This section explores the effects of invasive plants on ecosystems.

Grasses are particularly notorious for becoming invasive. Once planted there is little that can be done to contain them as they spread vigorously through roots and seed alike.

What Are Invasive Plants?

Invasive plant species are not native to a specific region, and their addition into an environment causes serious ecological consequences. Not all introduced species are invasive, but all invasive species have been introduced. Native weeds that grow naturally may be perceived as a nuisance to your garden, but they are not invasive.

Pictured above is common Teasel, once sold as an ornamental plant from Europe it is now found in all of North America, displacing local wildflower species.

Managing Their Spread

The best way to avoid an infestation of invasive plants is to never introduce them in the first place. Avoid collecting unknown plant seeds and adding them to your garden. Hand weeding can e an effective control measure if upkept for long periods of time, but depending on the species and severity of the infestation herbicides can be used as the last defence.

Caraganas have started being classified as invasive in Canadian provinces as recently as 2020, despite their aggressive spreading nature and difficulty to contain being well known for decades, they continue to be sold in nurseries to the present day.

Restoring Ecosystems

There are several methods for rehabilitating areas affected by invasive species. Some general guidelines are removing as many of the invasive species as possible, ammending the soil, and replanting the area with native vegetation. Weeding of the invasive species should be performed periodically to ensure the infestation does not begin again.

Learn About Our Commitment to Sustainable Ecosystems

This section explores our dedication to managing invasive plant species, emphasizing sustainability and ecological balance.

Below are some invasive plants commonly sold in nurseries and greenhouses, or that have been outlawed from being sold but may still be traded among oblivious gardeners.

According to the government of Canada, an estimated 58% of all invasive weeds were purposefully introduced for agricultural, ornamental, medicinal, or research purposes, before being classified as noxious weeds. Of these 58%, 52% were introduced as ornamentals for landscapes. Luckily the sale of such plants is largely regulated today, but there are still a few species that are up for debate due to their uncontrollable spreading habits and ability to colonize large areas when left unattended. Many invasive species are considered detrimental also for their ability to carry diseases that harm local environments, or because of their toxins capable of endangering livestock, or even human life. Below are a few examples of invasive plants that still openly sold but that are considered by a large number of professional gardeners to be invasive weeds. Strongly consider the possibility of these plants taking over your garden before purchasing them, and check their toxicity if you have any pets or children.

Trees

Norway Maple

Acer platanoides

  • Grows rapidly, forming a thick canopy that block sunlight and prevents the growth of other plants
  • Known to prolifically spead out of control, with seeds travelling long distances

Tree of Heaven

Ailanthus altissima

  • Invades open spaces and outcompetes native species

Russian Olive

Elaeagnus angustifolia

  • Fast-spreading and incredibly resistant to both hot and cold temperatures.
  • This tree outcompetes native species and is avoided by deer and other large grazers
  • Suckers are deeply rooted and regrow vigorously when cut

Shrubs

Caragana/Siberian Peashrub

Caragana arborescens

  • Newly recognized as invasive in Alberta and Minnesota
  • Efforts have very recently begun to remove the plant from parks and woodlands where it has spread

Barberry bushes

Berberis vulgaris & thunbergii

  • B. vulgaris has long been on Canada’s invasive list as it hosts black stem rust which is a major threat to cereal crops
  • B. thunbergii has recently been found overtaking woodlands in Ontario and Minnesota

Winged burning bush

Euonymus alatus

  • Declared invasive in most of the US and in Ontario
  • Dense thicket forming habits and substantial seed production make the spread of the plant near impossible to control
  • Turkestan burning bush (Euonymus nanus ‘Turkestanica’), is a good non-invasive substitute

Non-native bush honeysuckles

Lonicera morrowii,  L. tartarica, L. xylosteum

  • Spread long distances by birds
  • Invade large areas and choke out native plant species

Ural false spirea

Sorbaria sorbifolia

  • Aggressive suckering habits make it so that the plant spreads wildly out of control
  • Entire areas are engulphed in dense foliage, and roots are very difficult to fully dig up

Herbaceous

Bishop’s goutweed

Aegopodium podagraria)

  • Almost impossible to eradicate once planted
  • Shade and drought tolerant, will spread with ease to all areas of the garden and beyond, choking out all other plants as it goes
  • Very commonly sold in nurseries

Lily of the Valley

Convallaria majalis

  • Easily escapes cultivation and forms mass colonies in woodlands, displacing native plants
  • All parts of the plant are highly toxic

Baby’s Breath

Gypsophila paniculata

  • Significantly devalues livestock and wildlife forage
  • Prolifically spreads through thousands of tiny seeds

Cornflower/Bachelor’s Button

Centaurea cyanus

  • Classified as invasive in Canada and three US states. Absolutely prohibited in North Carolina
  • Spreads prolifically by seed and takes over native ecosystems
  • The sheer volume of seeds produced make this plant extremely difficult to contain
  • Seeds sold at nurseries and part of ‘wildflower’ mixes

Ox-Eye Daisy

Leucanthemum vulgare

  • Fast spreading through seed and roots alike, form dense clusters that displace native vegetation, especially wildflower

Yellow flag iris

Iris pseudacorus

  • Quickly degenerate wetlands by forming dense matts that encroach on fish habitats and bird nesting sites
  • Will eradicate native wetland species through overcrowding and excessive water absorption
Visit the government of Canada website for a complete list of plants currently identified as invasive, or the canadian council on invasive species PDF for a list of suspected harmful plants
Gov.CA Invasive Plants Field Guide
Canadian Council Invasive Species