The best time is in spring, i've left mine too late to do now.
Remove the off sets or buds carefully, making sure that they have plenty of their own roots attached. I believe that you can do it with the large buds too by carefully using a spade, but ive only ever dared to divide the small buds off. Then just pot up . It is best if the clump is of a decent size and established too. Any chance of a picture?

I don't have a picture at the moment,but I will get one soon. In the meantime all i can say is that it is huge and i don't think the buds will fit in a pot! I would like to think they would a lot smaller in the spring.
By the way "she" survived minus 13 degrees this last winter just covered by her own leaves.

I see! bit of a problem, are you planning to plant them elsehwere in the gardne then? or you will have to get some huge pots! Mine survived -8C this winter even thou the buds got frozen for a few days, but i think it encourage it to be bigger this year. I've always read in lterature that G. manicata was meant to be less hardy than G. tinctoria, but you've proven thats wrong! or they are equal!

I will be planting her in two other places in th garden, but I will have to wait till next spring now.
Thanks for all your help.