You can cut off the spent bloomstalk all the way down to the rhizome, but you should not cut back the foliage. The plant needs its foliage to feed itself for next year's bloom.

Laurie

I like to tidy mine up after they finish blooming, pull the dead leaves away from the rhizomes and trim away any diseased or unsightly looking foliage. I also cut away the stalks that don't have seed pods on them.