I wintersowed them a few years ago with good results. I looked briefly and didn't find my old seed packet but I'm pretty sure that they were not surface sown. I gave away some plants but lost mine in short order to voles:(

I have sown them indoors in winter in a sunny window and they sprout well. I have also put them in the ground in the spring and they sprout nicely, too. I love the cardoon!

Sally

I also wintersowed my cardoons with good results. I believed I covered the seeds. I grow them as an ornamental and the bees love them.