How to Prune plantain lily 'September Sun'?
No pruning required

plantain lily 'September Sun' · Hosta 'September Sun'
Grow in fertile soil that does not dry out, in light or part-day shade; this cultivar will tolerate some direct sun. Shelter from cold, drying winds, and mulch annually in spring. Hostas in the ground may need watering during dry spells. See hosta cultivation for more detailed advice
No pruning required