Weeds are invasive plants which are not native to this area. They may have been brought from overseas as an ornamental garden flower, or mixed in with food crop seeds. However they got here, some of them are faring extremely well and are taking over at an alarming rate. You’ve most likely seen the yellow, button flowers of tansy lining the railroad, or the sea of purple thistle blooms in a nearby ditch or field.
Common tansy
But, why should you care? Well, these plants actually cause damage to our ecosystems. Weeds reduce biodiversity by choking out native plants which reduces the quality of food available for wildlife. Invasive species (plants, animals, insects, etc.) are the second most significant cause of extinction worldwide, after habitat loss.
Plus, weeds have a negative effect on us too. A large weed infestation can reduce the value of your crop, and can even cause health issues such as allergies. Also, landowners are legally obligated to monitor their land and control weeds listed as noxious or prohibited noxious under the Alberta Weed Control Act.
As a landowner that currently conserves seven natural areas, the Edmonton and Area Land Trust deals with multiple weeds. Each weed species requires a different method of control. Many variables come in to play, such as: type of root system; timing of flowering; proximity to ponds and creeks; and the extent of the infestation.
One very common noxious weed, which is probably even found on your own property, is Canada Thistle. Despite the name, Canada Thistle is not native to North America and is a very tough weed to get rid of. It grows extensively through its creeping root system, reaching 5 to 15 inches deep and spreading 15 inches wide. Did you know that pulling thistle actually activates the adventitious roots, causing it to spread and produce even more rosettes? Each flower blooming through late July to August, produces over 5,000 seeds!
Canada thistle. How many seeds would be produced by the flowers in this photo?
Because of its tough and trickster nature, we take an integrated approach to controlling Canada Thistle. Pulling may eliminate a small infestation, because our cold harsh winters can kill the bits of leftover roots, but large infestations are much more difficult to deal with. With limited resources, and our aim to be as environmentally friendly as possible, spraying chemicals is not always an option at EALT. In some cases, our volunteers chop the flower heads off of thistle, bagging and disposing of the flowers to stunt the spread of the infestation. We often use multiple methods, timed for before flowering, and aimed to increase winter kill as much as possible. Why not use our winter for some good?
EALT’s volunteers spend endless hours each year managing weeds on our natural areas. If you want to help us keep it natural, join our volunteer team at www.ealt.ca/volunteer.
Next time you have a problem with weeds, don’t just grab the sprayer or weed whacker, do some online research, find fact sheets on the specific species and learn more about the plant to help you manage the infestation more efficiently. Visit Alberta Invasive Species Council website (www.abinvasives.ca) for helpful hints.
