I have hundreds of day lilies.This year added new collection , when I went to deadhead three plants had a small day lily on old bloom stalk from the top.A week later they bloomed large blooms .WHY.....

It sounds like a proliferation:

https://www.daylilies.org/ahs_...

Since you have hundreds of daylilies, you may be interested in the Daylily Forum here on NGA also:

https://garden.org/forums/view...

We always like to see new members- more for us to drool over since hopefully you'll be posting pictures of your daylilies!

@kikkie,

Always good to have questions from new members. Could you elaborate a little more on it, and do you have any photos of the blooms in question.
I am not sure if the new large blooms were on the same old scapes, or if the new large blooms were actually on new scapes. I thought maybe you might be seeding the blooms of a bud builder on the old scapes (not unusual in my garden for them to be smaller) and then regular large blooms on the new scapes? Could you make that a little clearer for us.