One definition of a weed is a plant growing in an area where it isn’t wanted, which means that every plant has the potential to become a weed.
The first settlers arrived in Alberta with seeds for plants with food, medicinal or ornamental value. Plants that escaped cultivation spread quickly and are now considered weeds.
The government of Alberta developed two lists of weeds: prohibited noxious and noxious. Plants are considered prohibited noxious if they spread rapidly but are in the early stages of becoming invasive. This means that if they are controlled when found, they can be eradicated before they spread further.
Noxious weeds are ones that cover vast amounts of land. The chances of eradicating them are slim but it is best to control them before they take over more land. The list covers all of Alberta with different municipalities and climate zones. Plants that are a problem in one area might not be in another.
The provincial legislation allows each municipality to concentrate on the weeds that are a problem in their area depending on how destructive the weed is to the ecosystem and farmland.
None of the plants on either of the provincial weed lists are native plants. All have been introduced for food, medical or ornamental reasons.
Some can still be found at retail outlets.
These are a few of the prohibitive noxious weeds that may be found in gardens in Central Alberta:
l Himalayan balsam impatiens glandulifera, also known as policeman’s helmet, impatients, touch-me-not and Himalayan orchid. This plant is usually passed between friends, neighbours and at plant exchanges. It is a tall plant that thrives given any amount of moisture and is easy to grow from seeds, that is if you can catch the seeds.
Seed pods explode when ripe casting seeds up to 11 yards (10 metres) from the mother plant.
The following are noxious weeds. Unfortunately, these plants are often sold by mail order and the occasional garden centers and nurseries as ornamentals.
l Baby’s breath gypsophila paniculata is a heritage perennial that has escaped to cover roadsides and pastures in dry areas. This white perennial that is part of florist arrangements, has a long taproot and hates to be transplanted.
l Creeping bellflower campanula rapunculoides is another heritage plant that runs rampant in flowerbeds, lawns and in areas around old homesteads. This plant creeps via roots as well as self-seeds. Once established, it is hard to remove this plant. There are other bellflowers that are attractive and less aggressive.
l Scentless chamomile tripleurospermum perforatum has fern-like leaves with white and yellow daisies. The flowers are similar to those of oxeye daisy leucanthemum vulgare and shasta daisy.
The shasta daisy is the only one not on the noxious weed list but might soon be placed as there are some varieties are very weedy. When looking for a white daisy, purchase a named variety that will not self-seed.
l Dame’s rocket hesperis matronalis is a heritage perennial with purple flower growing up the stock. These plants spread by seed having escaped from old homesteads.
l Yellow clematis, clematis tangutica, becomes a problem in dry areas. Yellow flowers give way to fuzzy pods that blow in the wind, often settling along fence rows. The vines are very hardy and do not die back to the ground in the fall.
l Common tansy tanacetum vulgare was brought into this country by settlers as a herb. Its foliage is fern-like and gives of a distinct odour. Small round yellow flowers appear in August. The plant can be found in river valleys and the edges of roads. It spreads by rhizomes.
l Toadflax, linaria dalmatica and linaria vulgaris are a member of the snapdragon family. Yellow flowers appear along the spikes resembling small snapdragon plants. These perennials have invading roots, making it impossible to remove the entire plant without use of chemicals.
These are a few of the plants listed by the Alberta government but they are not the only ones that can be a problem. Any plant is escaping cultivation and hard to contain should be eradicated.
For the complete list of prohibited noxious and noxious weeds, visit an Alberta Agricultural office or view online at http://www.edmonton.ca/bylaws_licences/PDF/Weed_Identification_Book.pdf
None of the plants mentioned above will be available at the Red Deer and District Garden Club Plant exchange on May 24 or Lacombe and District Garden Club Perennial Exchange and Sale on June 3.
Linda Tomlinson is a horticulturist who lives near Rocky Mountain House. She can be reached at firstname.lastname@example.org.