My zone is borderline for F. japonica, but I've rarely let that stop me from zone-pushing something I really want. Just like my colocasias, musas, dinnerplate dahlias, and cannas. Sometimes I put mulch over them in preparation for winter and sometimes not. They just seem to carry on fine whatever I do. I suspect that may be the case with this plant. But I'll situate it in a micro-climate to be on the safe side. Up against the brick of the house should provide a bit of extra warmth and do the trick just fine.
