WPW is vigorous and hardy here in my Z5 and makes a nice clump.
There have been over 100 daylilies registered with it as a parent, but in all but 3 cases it's the pollen parent. My experience and that of everyone I have ever spoken to about it is that it is an extremely difficult pod parent.
Here's a little tidbit for anyone wanting to hybridize with it ............ TRY DIP POLLEN ON IT. One of those 3 plants registered as having it as the pod parent is a dip. I have found that it is much easier to set a pod on it with dip pollen, but still takes repeated attempts. I haven't grown these seeds out, so can't speak to their fertility yet.
It would be interesting to have someone look at the pollen under a microscope.
Edited to add that it's pollen sets pods on dips easily.
