The grass in the first pic is Deschampsia caespitosa 'Deschampsia caespitosa 'Northern Lights' (Tussock Grass). The one they really like is Phalaris arundinacea (Reed Canarygrass) in the second pic. I haven't been real good at keeping the little fences around the pots
. I planted some winter wheat for them last winter. They have been keeping it mowed all spring so I'd be surprised if it ever sets seed.