The gall of those thistles

13 Apr


A great why to learn about a certain plant is to notice it when it isn’t growing.

Happened to notice some large galls which turned out to be plentiful on last year’s Canada thistle stems. This is a plant I have some interest in though the ground was still frozen today so I was unable to take a piece of  root home to grow in a pot. Canada thistle (Cirsium arvense) actually isn’t from Canada but arrive here from France in the 1700s. The insect which created these decorative galls isn’t originally from Canada either, they were brought into the province of New Brunswick back in the 1970s from Europe to slow down the growth of Canada thistle. I was unaware of this gall creating insect known as Urophora cardui until today and it appears it can drastically reduce the number of seeds which will develop and be available for me to pick latter in the year.


Canada thistle grows incredibly quick, especially its root system and its roots and the young stems and leafstalks are edible, so I suspect it could be a good perennial plant to grow as an annual in the house during winter. I haven’t eaten this plant for a few decades mostly over concern with nitrates in this deep rooted perennial and some mention of some thistles being carcinogenic. With this in mind I am much more comfortable growing it as an annual in a pot or spreading fresh seed in a selected isolated areas.


In the wild supposedly 14 hours of sunlight triggers new stem growth and if I read correctly the newly emerging Urophora cardui from their last year galls enter the new Canada thistle stems when they reach about 12 inches high which gives me a little time to harvest some fresh stems as our day light hour are on the increase. Of course an insect that only eats Canada thistle is not something I’m overly concerned with consuming anyhow, though I’ll focus on the new young stems.


I’m hoping to find a spot in my area where these galls are not quite as common on the Canada thistle as some seed collecting would be nice from the female plants when ready.  Even with both Urophora cardui and myself wanting to eat Canada thistle the plant has no worries as it has been a very common plant throughout much of Eurasia and N.A. and should remain so. ciao


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