Hi Martin,
I have always had these in pots and buried during the growing season. I also have one year old Improved Celeste and Italian Honey (from Petals from the Past) in buried containers - thank God, all doing very well in the conatiners against the southern side of the house
Last year the pots I had them in had 1 inch diameter holes drilled into sides to allow for better drainage. I did get some roots coming out and growing into surrounding soil, also some roots growing out of top of container then down the side and into soil. I just sheared these off with a sharp shovel before removing the pot from the hole.
The real problem is the weight of the pots in the holes...the trees have really expanded over the years and I keep increasing the pot size when I root prune. So, it isn't fun lifting the pots out at the end of the season. Also, as you know, the "anti-frost shuffle" we do between the garage and the growing area in the early Spring gets tedious.
I'm quite sure the neighbors think I'm a little crazy in April and May, seeeing me wheel out the figs every morning on a hand truck then wheel them back at night...but it's well worth it in my opinion - especially when you're rewarded with a bowlful of beauties (like the ones I picked a couple days ago form the "Corrado Fig" in the photo below)!
Thanks,
Joe