How to Prune yellow daylily?
Cut back flower stems after flowering has finished. Remove dead foliage as required

yellow daylily · Hemerocallis lilioasphodelus
Also known as: common yellow day lily; yellow day-lily
Grow in fertile, moist but well-drained soil preferably in full sun. Flowering is likely to be poor in shadier situations. Tolerant of heavy clay and poorer soils. May need watering in spring to early summer in dry conditions to ensure flowering. See Hemerocallis cultivation for details
Cut back flower stems after flowering has finished. Remove dead foliage as required