Posted: 03/09/2016 at 12:39
I've done it at this time of year Verd, but you do often sacrifice flowers the following year. It just depends on conditions I think. If the plant's really congested, it's possibly doing it a favour to get it out. If it was mine, I'd probably repot it and then split it next year.
I know if I visit the nursery this week, they'll have loads which will have just been split and potted up. That's why it's best to buy one after flowering
As Verdun says, sun on the rhizomes - as much as you can provide.