My chicken yard is about 25x50. I keep 8-10 chickens and they keep this to bare dirt. It took them one summer to knock it down from grass over their heads (that was way cute, they established little tunnels) to dirt. We have since added an auxillary yard that we can close off to let the grass recover. They won't touch either nettles or thistles standing, but will eat them after I cut them down.
