@Natalie As my clumps of Stella have become larger and larger the amount of bloom and rebloom has gone down and down. There was little bloom this year and no rebloom. I have not divided them in more than 15 years or fertilized them. They are large clumps and the only bloom is sparse and on the edges of the clumps. The Stella are in beds with other daylily clumps close by. I split off three pieces this spring and they were planted in a new bed. They bloomed and rebloomed.
I would have to guess that your Stella is still blooming and reblooming because there are still resources, such as nitrogen, in their planting location that they have not used up or there are other sources. The central fans in a clump are the first to suffer and fans towards the edges of the clumps can mine new areas of the bed with their roots to get the resources they need. Of course if those new areas of soil are also being mined by the roots of other plants then the fans at the edges of the daylily clump will not do as well.
