Hello Jacob and thanks for your insight on winter temperatures in zone 6, a bit colder than here!
Cabbage are hardy but yes I think it’s worth using row cover, say from mid to late October, leave it on until snow melts sometime in March, or until early April if they look happy underneath, depending whether you have a lot of wind.
I have not tried this so cannot be certain, shall look forward to hearing how the cabbage fare.
