Posted: 16/09/2015 at 23:17
I would cut them back now.
use the cut material for cuttings.....not too lste. A mixture of 50/50 mpc and perlite. No, don't root prune. However the hardier spreading vwrieties often root/layer themselves so check for this. you can pot these up.
Which varieties incidentally? The less hardy ones will need slightly better protection over winter
In many areas osteos will not make many flowers now so you won't lose anything by cutting back plants now. Besides you will need your plants to be as compact as poss in a possibly crowded gh