My 10 chicks are 8 weeks old, and I am not free ranging them yet. Since they are confined to the coop/run, I throw a handful of spinach a couple times a day and would like to also throw a flake of alfalfa hay (they absolutely love it!) in for free choice greens. Is it ok to offer free choice? I know when they free range they eat grass, weeds etc "free choice". Any thoughts on this? Do I need to wait until they are older, and if so how old?