How to Prune waterfall gladiolus?
No pruning required

waterfall gladiolus · Gladiolus cardinalis
Also known as: cardinal red sword lily; corn-flag; New Year lily; superb gladiolus
Grow in a well-drained soil, or pots of free-draining compost, in a sunny, sheltered position; best lifted and allowed to dry off in late summer after flowering. Repot in autumn and place in a cool but frost-free greenhouse; plant out after all risk of frost has passed
No pruning required