How to Prune plantain lily 'Bressingham Blue'?
Remove spent foliage as required and remove dead foliage when it dies back at the end of the growing season

plantain lily 'Bressingham Blue' · Hosta 'Bressingham Blue'
Grow in fertile, moist but well-drained soil in part shade with shelter from cold dry winds.
Remove spent foliage as required and remove dead foliage when it dies back at the end of the growing season