Customer focused on one thing - to design the decorative grass with fluffy flowers like the main accent in the perennial flower bed. It was eassy to guess he was talikng about Pennisetum villosum which has gained paticular popularity during the past several years in Lithuania.

This plant is very beautiful for sure. It decorates environment and draws attention, but the problem is it becomes more annual rather than perennial in Lithuania climate. The goal was to create long-lived, low-maintenance, decorative all year round flower bed, so Pennisetum was "off topic".

I was looking for alternatives, and soon found it. Calamagrostis brachytricha has all desirable properties. Piet Oudolf marks this grass with even three stars. Three stars from known planting design goes only for those which are robust, has very good structure all year round and decorative flower heads in winter time. 

There are some planting design examples with Calamagrostis.