Depending on the size of the run and the number of chickens you have, I am pretty sure any grass will be turned to dirt in a short period of time. Many will use pine shavings as a bedding layer on the dirt once the grass is gone. Others use sand.
Me, my coops can be moved like a tractor, so I leave mine as a dirt floor until I get around to moving it.
I have a rather shallow water table so any rain mucks up the backyard for a couple days. I put down a good layer of straw and change it out once a week or as needed. We also compost a ton of our yard clippings, any weeds from the garden beds, coffee ground etc, so occasionally I'll put a thick layer of compost for the hens to dig in they seem to enjoy finding bugs and worms to eat. Edited by Gabej - 3/24/16 at 7:09pm