I have no experience with them, but did you trick them into thinking they were in their second growing season? In other words, expose them to low temperatures after the higher ones that you grew them as transplants in? I have read that, that is necessary to get the buds. They sure look like a pretty plant, the violettas.

Also, I have read several very old references to people overwintering artichoke roots. I don't really know anything about it though.

Good luck!

Here is a link that might be useful: Ottawa Hortiphilia

I am planning to raise some chokes in pots here to move to the farm later when I am there more. I know this is an old thread but I hope to revive it some. Happy gardening!