protecting container plants in winter (that can't be moved)
If you have a plant in a container that cannot be moved in winter, say it's too large, for example, and it's normally hardy in your zone, is mulching around the pot usually sufficient?
Say you have a "patio" or dwarf type fruit tree in a container hardy to zone 6. It's reached a point where it's large enough that moving it is difficult or it's too large to store in a garage, coldframe, etc.
The old rule I've heard is that you are really two zones colder, effectively, for a plant in a container, since the pot is exposed on all sides, whereas an in-ground plant only has cold exposure from the "top" of the rootball...so, if this plant is in zone 6, it would have to be approximately zone 4 hardy to survive.
If, rather than attempt to move this plant, you mounded up some type of mulch around the sides of the pot, maybe a little on top as well, has anyone done this? If so, what are the best types of mulch, and how much would you need to be effective?
What about other methods?