Stone dust or coarse sand ( the kind used in concrete) is best. Drains well and chooks have a supply of grit to boot. Any organic matter will cause moisture to be held longer in soil. I am using grass clippings and leaves, but then my run has a 5:1 slope, so it never gets mucky, ever. If I keep on adding enough clippings and leaves tho, it could get mucky late in the winter. I am going to make 6'x6' frames fro recycled deck boards to be covered with chicken wire to place around the run after cultivation and seeding. Chooks will have fresh grass to eat but cannot tear up roots and destroy it. Has been on my to-do list for month and is best done over the winter to get best results without having to irrigate/sprinkle.
