I'm in 6b too. You should be fine burying them *if* you have an area that is sheltered.

I have a small Autumn Moon in-ground in a sheltered area in the lee of my house, it made it through the terrible winter we just had with no dieback. I had no problem with trees in pots that I mulched in nearby against the house. However, I lost a Tsuma Gaki and a Kasagiyama that were in more exposed areas of the landscape. FWIW, my Bloodgood was fine in a very exposed area, but it is also a *lot* bigger.

Thanks ysrgrathe. I am in RI. What do you mean sheltered? Like something overhang with roof? My back yard northern side is fenced. Will it ok they are buried close to the fence? Thanks again.

I'm not an expert, but I think the most important factors are protection from wind and sun. Wind dries and can lower effective temperatures, sun can lead to frost cracking and other heating damage when the roots are frozen. Your location near a fence sounds like it could be good if it is a buffer from prevailing winds and the winter sun.

Here in 5a I have overwinter JM without problems in pots, either in my compost pile or sandwiched between 2 hay bales (with the gaps stuffed with more hay and hay piled up around the tops -- that was this past nasty winter where temps dropped to -18F). Mine was a Bloodgood and an unknown variety. I don't know if your others are perhaps more tender.