How to Prune Kerner iris?
Remove any dying foliage in autumn, old flower stems can be cut down after flowering. Tall varieties can have their leaf fans trimmed to one third of the total height to reduce wind rock while the plants are establishing

Kerner iris · Iris kerneriana
Grow in well-drained, neutral to slightly acid loam in full sun or partial shade
Remove any dying foliage in autumn, old flower stems can be cut down after flowering. Tall varieties can have their leaf fans trimmed to one third of the total height to reduce wind rock while the plants are establishing