I gave my original flock a little over 100 sq. ft each in my run. I kept grass in it that first year, but my birds were allowed to freerange in the evenings and weekends. They're rarely confined to the run these days, so of course it still has grass. I think if they'd been confined to the run 24/7 that first year, the grass would have been gone by the following spring...being eaten down as it tried to regrow after winter... If you can freerange at least part-time, and have a pretty big run, it IS possible to keep grass in it.