I've grown cardoon on and off for about 5 years now. The first year the one plant I put into the ground flourished, becoming huge and beautiful. It didn't survive the winter though. The next year I had two pretty nice plants in the ground, and for whatever reason they both overwintered, giving me those huge, wonderful thistle-like blooms the next year.
Other years I haven't had much success -- the plants stayed small, or just never really looked that good. This past year I planted four cardoon seedlings, and -- as expected -- had varying degrees of success.
The one that was planted in the raised bed made from a bottomless pot did the best -- as seen in the photo above.
It's not the best specimen I've ever grown, but it's in the top three I'd say. I'm quite happy with it.
If I remember correctly, even though I started all four plants from seed indoors at the same time, I planted this one into the ground a bit earlier than the other three, which probably explains why it did the best.
The other three all went into the ground at the same time, each in a different planting bed. This one sort of crept along, staying small for most of the summer. Then as the end of the growing season approached, it really took off:
When compared to the first plant, this one looks quite different. The leaves are much thinner, and more "toothy":
If I didn't know any better I'd say that these weren't even the same species.
This one I planted near the purple fountain grass, and it was quickly overpowered by the faster-growing grasses:
I had forgotten it was under there. Needless to say without much sunlight it really didn't grow very much at all. It's still alive though, so I'll protect it for the winter and see what happens.
The final plant had all the sunlight it wanted, but still never really grew much:
Even though we had a dry summer, I watered all of these quite frequently (I read that cardoon likes water). I really don't know why this one didn't get any larger.
I will mulch each of the plants and cover them to keep the crowns dry over the winter -- crown rot is a problem with this plant in my climate. Even protected it will be lucky if I get any of these to survive the winter. If they do though I will be very excited!
Even though I didn't have complete success with the cardoon this past year, I'll start some more seedlings this winter. I'll make sure they don't outgrow their containers though, as I suspect that's one of the problems with the plants that didn't do very well.
I'm definitely going to keep trying!