The climate in some locations in California is conducive to rebloom.
Hybridizers in both California and Florida have indicated that nearly all daylilies rebloom in their growing conditions and locations (that includes cultivars that were not registered as being rebloomers and even daylily species).
Hybridizers may tend to grow their daylilies under optimum fertilizing and dividing conditions.
I have been test fertilizing some of my daylilies with high nitrogen. When I do so I get rebloom.
I grew 'Mosel' for many years under average conditions - it had never rebloomed. I then started giving it high nitrogen fertilizer several times a growing season. The first year it just grew bigger but did not rebloom. The next year it rebloomed. It then rebloomed each year I gave it fertilizer. After I stopped fertilizing it stopped reblooming.
I grew 'Ophir' for many years under worse than average conditions. It never rebloomed. I then gave it high nitrogen fertilizer and it showed the same behaviour as 'Mosel' - it is reblooming right now.
This is a list of daylilies that have bloomed this October here on rebloom scapes and that I had fertilized with high nitrogen:
American Freedom
Don't Mess with Me
Lemon Picasso
Wide Load
Bubbling Over
Cherry Valentine
Ophir
