The grass isn't going to stay. All the beautiful grass filled run pictures you see are when the chickens are new to that coop or a brand new run. The grass will become a barren mud flat so some type of bedding/ litter has to be used even in the run. I used the deep litter method with hay all last year in a covered run. Ladies have a roost 'box' w/ chunky sawdust under it so I scoop poo every morning and just toss it out in the run. The entire run gets flipped and turned with the hoe each morning and clean hay added as needed. Never had a problem. I have heard so much about sand that I will be switching to using it in the runs this year. If all goes well I may use sand in warm weather and in brooder then deep litter hay in cold weather for warmth.