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Alberta Invasive Plants

What is a noxious weed?

Noxious weeds are invasive plants that are considered a danger to the ecosystem due to their extremely aggressive nature. Many were introduced as garden plants but have escaped into the wild, where they out compete native vegetation and in some cases alter the local habitat to the point where native species of flora and fauna can no longer live there. These plants are regulated by the Alberta Weed Control Act and it is the responsibility of property owners within the province to keep them under control.

What is a prohibited noxious weed?

A prohibited noxious weed is a plant species that is known to have an invasive nature, and has become a major problem in other areas, but is not yet common in Alberta. These species, also regulated by the Alberta Weed Control Act, must be destroyed if they are found on your property.

Depending on the bylaws of your local government, you may be served a notice if noxious weeds are found on your property, and if you fail to remove them within a reasonable time frame, you may be invoiced for work that is contracted out to remove them for you.

Common Noxious Weeds

Many noxious weeds were originally introduced as garden plants, and are still found in many gardens today. While they can be pretty, they can also be very difficult to deal with. Some of these are sometimes confused with garden plants which are not noxious weeds. Note that Greenland does not sell any of the plants listed as noxious weeds or prohibited noxious weeds by the Province of Alberta. The following are plants with some ornamental value that are still commonly seen and sometimes asked for by customers, which are regulated by the Alberta Weed Control Act:


Baby’s Breath
(Gypsophila paniculata) – noxious weed

  • Description: well-known in flower arrangements; produces airy clusters of white flowers held above the foliage; seedheads form “tumbleweeds” in the winter.
  • Plant instead: German stattice (Goniolimon tataricum)

 

Bighead Knapweed (Centaurea macrocephala) – prohibited noxious weed

  • Description: also known as golden thistle, this is a tall-growing plant, up to 6 feet, with large and coarse, hairy leaves, and showy yellow flowers that resemble cornflower or bachelor’s buttons.

  • Often confused with: mountain bluet or bachelor’s buttons (Centaurea montana) and related garden cultivars and hybrids, which are not noxious weeds.

  • Plant instead: mountain bluet or bachelor’s buttons (Centaurea montana), Persian cornflower (Centaurea dealbata), cornflower (Centaurea ‘Amethyst Dream’), giant scabious (Cephalaria gigantea). Note that these can be aggressive growers as well.

Creeping Bellflower (Campanula rapunculoides) – noxious weed

  • Description: It produces arrowhead-shaped leaves with a jagged edge, and tall spikes of purple bell-shaped flowers up to 3 feet in height all season.

  • Often confused with: harebells or bluebells of Scotland (Campanula rotundifolia), a native species, and clustered bellflower (Campanula glomerata), a common garden plant; neither of which are noxious weeds.

  • Plant instead: harebells or bluebells of Scotland (Campanula rotundifolia), peachleaf bellflower (Campanula percisifolia).

Himalayan Balsam, Himalayan Orchid, or Poor Man’s Orchid (Impatiens glandulifera) – prohibited noxious weed

  • Description: Rapid growing annual that produces tall, reddish stems which may reach 8 feet in height, with large, toothed leaves and pink flowers which are tubular in shape. The seed capsules notably explode at the slightest touch, propelling seeds many feet away from the parent plant.

  • Plant instead: Tall garden phlox (Phlox paniculata ‘Laura’), Joe pye weed (Eupatorium maculatum ‘Atropurpureum’)

 

Japanese Knotweed (Fallopia japonica) – prohibited noxious weed

  • Description: This plant, and especially its variegated form, have been planted as ornamentals in the past. It is a large and bushy plant to 6 feet tall with attractive foliage and feathery plumes of white flowers.

  • Often confused with: giant fleeceflower (Persicaria polymorpha), which is related and has a similar appearance, but is not a noxious weed.

  • Plant instead: Giant fleeceflower (Persicaria polymorpha), giant goat’s beard (Aruncus dioicus), yellow waxbells (Kirengeshoma palmata)

Ox-eye Daisy (Leucanthemum vulgare) – noxious weed

  • Description: A classic daisy look with white flowers that have a yellow centre.

  • Often confused with: Shasta daisy (Leucanthemum x superbum), a common garden plant that is not a noxious weed.

  • Plant instead: Shasta daisy (Leucanthemum x superbum ‘Becky’)

 

Purple Loosestrife (Lythrum salicaria) – prohibited noxious weed

  • Description: A tall and bushy plant that produces spires of purple flowers in the summer.

  • Plant instead: blazing star (Liatris spicata), Salvia (Salvia nemorosa ‘Caradonna’), culver’s root (Veronicastrum virginicum), hybrid speedwell (Veronica ‘Purpleicious’)

     

Tamarisk (Tamarix ramossissima) – prohibited noxious weed

  • Description: a very unique and beautiful shrub, it has airy branches with scaly foliage similar to a cedar, but the top part the shrub (which exceeds 10 feet in height) is covered in pink flowers.

     

 

Yellow Flag Iris (Iris pseudacorus) – prohibited noxious weed

  • Description: Looks like a Siberian Iris with yellow flowers. Produces grassy foliage and grows up to 3 feet in height. Flowers appear in early summer.

  • Often confused with: blue flag Iris (Iris versicolor), a native species now becoming widely used as a water Iris, and Siberian Iris (Iris sibirica), a common garden plant.

  • Plant instead: blue flag Iris (Iris verisicolor), Siberian Iris (Iris sibirica).

Yellow Clematis (Clematis tangutica) – noxious weed.

  • Description: Large and vigorous vine capable of growing up to 20 feet in length, full of pendant, bright yellow flowers all summer, followed by fuzzy seedheads.

  • Often confused with: white Clematis (Clematis ligusticifolia), a native species with small white flowers; and alpine Clematis (Clematis alpina), a common garden plant.

  • Plant instead: white Clematis (Clematis ligusticifolia), alpine Clematis (Clematis alpina).

    More information on invasive plants in Alberta can be found at https://www.abinvasives.ca/.

 

 

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