Geraniums

I planted several purple geraniums on my scented bed because I read that they were good ground cover and also deterred greenfly.

They have been very successful indeed, spreading like wild fire and blooming endlessly (as they are still doing).

I would like to split them and plant some of them somewhere else. Can I do this? - and if so when? I would not like to disturb them yet as they are in full flow.

Lots of thanks for your help.