Iris in the ground on the south side are different than iris in pots on the south side...............especially black pots. I have a large bed on the south side of my house that do well and bloom sooner but iris in pots on the south side would freeze and thaw as the weather fluctuates. This goes for all plants overwintered in pots. This has been my experience and has been successful for me. A friends grows many hosta in pots and he handles them the same way........
