I'm going to answer assuming you're asking about run bedding.
The grass is great for them, unfortunately it wont last unless you can move your coop. If that were the case i think that grass would be ideal. I like wood shavings for run bedding because of the rate that it composts and ease of shoveling. But any run bedding tends to keep the ground wet underneath. If you have a few acres of trees and a wood chipper you have basically unlimited bedding at hand.
They require some dry dirt so that they can bathe. Small sandbox with sand mixed with wood ashes works well to compensate for the bedding.
