One has to sort out if what you are seeing is just a weather related mutation or some hidden genotype that is trying to express itself. And stabilizing anything new so that it appears consistently takes many generations.
Unless a weather related effect is present in most or all daylilies it is almost certainly genetic. That is, the plant that shows the effect is genetically different from the plants that do not show the effect. This is basically the situation for all similar effects caused by any factor not just the weather. Such effects/characteristics are described as having thresholds. There are probably many important characteristics now present in daylilies that have such thresholds. They can be altered by selection.
The standard example involves the fruitfly. If fruitflies are given a temperature shock while developing, some of them will have a break in a wing vein when they are adults while others will not. There is no break in the wing vein without the temperature shock. The researcher crossed the fruitflies with the break together and gave their offspring a temperature shock while they were developing. Some of them developed a break in their wing veins. The researcher repeated the selection process for a number of generations. After a few generations of the selection with temperature shocks finally the break in wing veins appeared without temperature shocks in a few fruitflies. Breeding from that generation on was with fruitflies that had the break in their wing vein without the temperature shock. As is to be expected, the proportion of fruitflies with a break in their wing vein without having suffered a temperature shock continued to increase generation after generation. A characteristic that only appeared uncommonly in a few fruitflies because of an outside factor became a characteristic that appeared in many fruitflies without the outside factor.
These sorts of characteristics are based on the actions of many genes (as probably are most characteristics in daylilies).
I suspect that a substantial number of the unusual characteristics that are present in modern daylily cultivars and that set them apart from the species are based on threshold characters. Picotee edges could be one. Double flowers could be another.
