Established Hameln Grass rotting from center

Question

I have 40′ of Hameln grass planted on a bank along my driveway. The plants are about 5 yrs old and are about 1′ wide. Several of the plants are rotting from the center of the plant out. We trim the plants each year in the spring before they start growing to about 4″. We try to remove the dead stalks and the rot each spring but it is getting progressively worse. We do mulch with bark mulch. Prior to planting the Hameln grass, the bank was planted with spirea which died off due to fire blight. We live in VT in zone 5. What can we do to improve the health of these plants?

Answer 1

Regular division of ornamental grasses should be done either every year or every other year to help prevent die back of the center of the grass.

https://www.gardeningknowhow.com/ornamental/foliage/fountain-grass/tips-for-care-of-fountain-grass.htm