Jay

Adam, I'm in zone 5b/6a. A little colder than you, but not that much. I have a set up for my trees in the garage (unheated) by a window. I have wintered my Elms, Hornbeams, Japanese Maples and others in this location with good results. The garage moderates the temps and keeps the trees out of the cold drying rain and wind. The most important thing to do is to prevent the roots from going through to many freeze- thaw conditions.

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A Bonsai student living with his trees at N 44.37 W 77.49...
Think before you act... then think again... no good comes from rushing