Old clumps may be thinned by carefully cutting out the old divisions at the centers of the clumps and leaving new growth in the ground. In the case of very old and compacted clumps, the process of thinning might be easier if you dig up the entire clump, remove the old "spent" rhizomes, trim the foliage of the new rhizomes and replant them. Smaller shoots may take two years to produce blooms, but larger shoots should bloom the following spring.

You can cut the leaves down to a tidy fan but not too short for a few weeks to allow the rhizome to build up some energy - weak feed with tomato fertiliser will help (as with bulbs).

Many thanks for replies...John.