Zone 6 ?

I'm counting on global warming :O)

(I've got some small Z7 & Z8 stuff sitting out there -- just running an experiment & keeping my fingers crossed, so to speak... The Araucaria survived last winter - not sure it will repeat that feat again this year though...)

First, turn off the capslock key. Second, protect against the drying winds. It's been my experience the potted trees really take a beating when weather systems from the Artic hit. In short, you answered your own question with the mulch and and leaves cover solution. Also, placing them in a garage helps.