According to Erwin and Heins (1990), lily is thermomorphogenetic, which is why the
two factors light and temperature are strictly linked and their effects are often confused.
Smith and Langhans (1961) found that different combinations of light and air temperature
were able to produce plants of the same height, whereas temperature rather than
photoperiod affects flowering time and the total final number of flowers. According to
Molfino (1993), temperature is the critical factor, given that Lilium shows optimal
growth between 13 and 25°C, which is why he advises considerable temperature
reductions during the hot season.