For bearded irises..... My understanding, and I am by no means very knowledgeable about such things, is that a rhizome only has only so many little buds, or places on the rhizome where a new plant/fan will grow.
If you have noticed a potato has what we call 'eyes' where a new potato plant may sprout. Once all of these areas have exhausted themselves the potato cannot make another plant. A rhizome works the same way. Once all of the buds have produced a new fan the rhizome will not produce any more. I hope this is not confusing. I don't know the technical terms for the buds, or places on the rhizome where a new plant/fan will sprout from.
