why does the foliage of daylilies turn yellow?

Question

East coast. 4 seasons.

Answer 1

If they have finished flowering for the season, then it is likely going dormant. The plants could even enter dormancy early as a result of the hot temperatures affecting much of the country. For additional causes of leaf yellowing, this article should help: https://www.gardeningknowhow.com/plant-problems/environmental/plant-leaves-turn-yellow.htm