Last year we planted cardoons in the demo garden, and they became impressive plants:
although didn't make it to flowering stage. In the fall, I cut down the stalks and prepared the roots for winter as suggested: mulching well with leaves, placing a bucket over each plant stub, and tying the whole thing down with black plastic on top. Then came the arctic blast of this winter, and despite the protection, I didn't expect the plants to survive. But, a couple of weeks after we took all the plastic stuff off, they are back and growing:
Now the interesting part, because I also had a cardoon plant in my community garden plot, which never achieved anything like the height and breadth of the demo garden plants (it's the soil). I decided to let it die, and didn't mulch it at all. You would think the repeated hard freezes of the winter would have done for it. Nevertheless:
And that was a week before the plants in the demo garden showed themselves. I'm impressed. I've had cardoon plants overwinter before (see below) but only in the wimpy zone-8-like winters. Perhaps the frequent snow insulation helped, or else this is a hardier variety than I've grown previously. (It's called Avorio, and claims hardiness to zone 6, though I didn't actually believe that!)
Unfortunately I have planned a tomato plant for that space in my community garden plot, so I'll have to dig up the cardoon and move it somewhere else.
Cardoons are a close relative of artichokes, grown for the edible leaf stalks rather than for the flower bud. The stalks are better if blanched by wrapping the plant, which I admit I don't usually do, because it's so ornamental and dramatic if left alone. Here are some of those winter survivors from a few years back, with me as measuring stick:
And a closeup of the flower, which is why you want it to grow a second year (flowering the first year is possible but not common in my experience).
Very popular with bumblebees! Crossing my fingers for flowers this year for the demo garden plants.