In the past I have lifted the clump in the spring and divided the clump with a spade. or you could put 2 garden forks back to back in the middle of the clump and push them apart .

welcome to GoY too stella ;o)

I used to grow these for shows many years ago - I just waited until new shoots were starting to grow at the base - then when about 3" long I would cut them at the base - put rooting powder on the ends and plant them into a good compost - Never had any problems doing them in this way -

Yes that is a quick way to propagate them. I do the same with Dahlias too.