Posted: 10/03/2014 at 07:37
If it's a big one that's going to be quite a task - but what you do is you cut any remaining leaves back to the base of the plant and dig up the root with a good sized rootball.
The root will have several shoots - each healthy shoot will make a new plant. Split the root so that each piece has a well formed healthy shoot and plenty of root - depending on the size of the root you may be able to do this with two spades back to back, or you may even need a rip saw.
Plant each portion in a well-prepared water-retentive area of boggy soil and stand well back