Canada thistle.

Well, we’re digging ourselves out of a “nearly spring” storm here in Calgary – we received approximately 20 cm (8″) of snow yesterday and flakes are still falling as I write this. Just two days earlier, we were basking under +12°C (53.6°F) sunshine, which is pretty typical of the way the weather goes around here at this time of year. I was delighted to get out on Friday morning and take a walk up on Nose Hill, where I ended up sharing the sunrise with five deer and a grumpy porcupine (you can see one of my photos of him here).

While I was up on the hill, I noticed that the City’s war on Canada thistle (Cirsium arvense) in the park is ongoing.  I don’t like the fact that herbicides are sprayed annually to control this nasty invasive, but if something wasn’t done about them, the whole park would be covered in thistles. Pulling them simply isn’t a good solution – and it’s not just because they are thorny!

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Canada thistle (winter)

CRAZY FACTS ABOUT CANADA THISTLE:

  • Canada thistle is not a native of Canada. It actually has its origins in Mediterranean Europe.
  • Another common name for Canada thistle is creeping thistle…as in, it “creeps you out” with its insane root system. 😉
  • Each plant can produce up to 5,000 seeds.
  • Each seed can remain viable in the soil for up to 20 years.
  • Just 8 to 10 days after flowers emerge, plants can already produce viable seed.
  • Canada thistle reproduces by seed AND by vegetative cloning – a double whammy.
  • New plants can form from the tiniest of root segments – just 3-6 mm (1/8 – 1/4″) thick and 8 mm (3/8″) long. This is why pulling and digging don’t do diddly.
  • The tap root of each plant can reach 6 m (20 feet) underground in a single growing season.  Isn’t that incredible?¹

I am sooooo glad I don’t have to battle Canada thistle in my flowerbeds! I have a severe problem with quackgrass (aka couchgrass, Elymus repens), however, which I have struggled with for over a decade. While I have made significant inroads, I cannot ever let my guard down….

What are your worst plant enemies?

¹http://www.agriculture.gov.sk.ca/canada_thistle_control