I can't, I'm afraid - this plant isn't available over here yet, although from what I've seen, it is relatively hardy, and I can find no details anywhere that describe how to propagate it. It seems to form rosettes on the ground around a central stem - I wonder if those rosettes eventually form roots quite naturally and then grow on their own. Sounds like that might be a possibility, but I expect patience is required for that to happen. You don't say whether the rosette you removed and replanted actually had roots or not, so I can't comment on that.

I , too, have several Lobelia Aberdaric and they get lots of admiration. I wanted to propagate but have been unable to find out how(few growers are prepared to part with their secrets as they make money out of selling these gorgeous plants) but I have a thoery......the trunks,if on the ground, will root and further growth will appear(another rosette). Should you wish to propage make sure the trunk is resting on the soil(mine were surrounded by gravel and then one day, the kids dug a hole and exposed some earth and a few weeks later, little roots !!) and see what happens. Mine are dying as they are planted on top of clay and are rotting, so this is my plan......I will try and transplant one into well draining soil and cross my fingers!Good luck and let me know if I am barking up the wrong tree...!