Hybridizers in both California and Florida have indicated in the past that in their locations and growing conditions nearly all daylilies will rebloom.
Researchers have determined that daylilies do not need to experience cold to flower nor do they require specific day lengths (or night lengths) to flower.
So basically a daylily will flower, depending on how often the gardener waters and fertilizes and how long the growing season lasts and what the temperatures are during the growing season. When temperatures are too high (above the daylily's maximum temperature for growth) it will stop growing. When temperatures are too low (below the daylily's minimum temperature) it will stop growing. The daylily needs to grow to be able to rebloom. If it rests (stops growing for any reason) then the chances that it will rebloom will depend on how long it rests and how quickly it grows after it stops resting. Plant growth including daylilies is fastest at the plants optimum growing temperature (probably about 80F or below for most daylilies - probably higher for Florida-breds that have not had northern-breds in their ancestry for many generations). Plant growth is also fastest at the plant's optimum nitrogen fertilizer rate, etc.
Rebloom may be more likely if the daylily is not allowed to set seeds.
