It's an extreme example, but Matthew Kaskel had trouble getting most daylilies to bloom in Homestead, FL.
It is very important to understand that evergreen daylilies also would not flower. Kaskel's observations on the problem were that early bloomers were better at flowering under Miami growing conditions and mid-bloomers were worse. Early bloomers experience lower temperatures while developing than later bloomers. It should also be emphasized that some evergreen daylilies hybridized in Florida were not necessarily any better at flowering in Miami conditions.
Those observations emphasize that daylilies are not necessarily adapted to extreme growing conditions. High temperatures are one factor that causes many plant species to not flower. Experiments by Arisumi determined that some daylilies may not flower at all when grown at 85F or 95F. He found around 75F to be an optimum temperature. I have used first flower open times and growing degree days and determined that for 'Barbara Mitchell' and 'Pardon Me' around 78F is a reasonable estimate of their optimum temperature for flowering.
@JamesT
Do you have personal first-hand knowledge of this solution? My information is that he used a different solution, when necessary.
His solution was to have northern growers send plants to him in January/February, plants which had already experienced winter dormancy.
