In the AHS 2002 Handbook there are some nutritional tests detailed and they did look at scapes. I would have to look at the book to jog my memory of what was said - it's not handy right now.
At least the first buds are set before winter in this area and then subject to however cold it gets at crown level during extreme cold winters here. I'm not sure that it would be lack of water either since I don't water my daylilies and I don't see shorter scapes, although our climates are different.
I'm sure others will have some thoughts. I'll post back later with whatever the Handbook says unless someone else gets a chance to look it up first (it's at the end of the physiology chapter).
