Good grief Anna.
If they are sorta dormant, the roots should not grow much over winter. But OTOH, if they are in a warm GH, they may not go too dormant and the roots might continue to grow. They will all be in a heated GH - right?
I do not have experience doing so, But unmixing the roots brings a ? to mind. Unbarrel them and take a hose to them to facilitate unwinding the root mess in Spring? I do that all the time when I am separating Iris or particularly daylilies. They always come out ok. I don't know how tuff the Brugs roots are - only my second year growing them and I only have 3 larger plants in post and about 15 seedlings - all less than a foot tall at this point.
You could try some each way - keep the big guys separate in their own pots and put some smaller ones together in the barrels? Maybe try some of those plant bag things. They would likely take less space, but added expense if you have to buy them.
MG - you must have a thousand cuttings. Heh Are you going to root them as well?
