Answer: Unfortunately, the Japanese bluberry tree is not winter hardy in your area, it is only winter hardy into zone 8. (Your zip code places you in winter hardiness zone 6.)
It is very difficult to maintain woody plants (trees and shrubs) in containers year round outside. The winter is very stressful on them, in part because their roots are not insulated from the cold the way they would be if planted in the ground and also because the roots are constricted into such a small space.
Since you kept arborvitaes going, you must have a spot well suited to them. I would suggest you use them again.
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