Mine have eaten every scrap of grass they can find, but in addition to feed I will toss piles of cut grass after my dad mows, & fruit & veg scraps & crushed egg shells. Their yolks are very dark but they just started laying.Chickens also do not get "vitamins" from free ranging. If you've ever wondered why a free range chickens' yolk is darker than a chickens' yolk that is living in a run, it's most likely because they have access to dandelions. (Which of course, you can have grass and flowers in your run, you don't have to have bedding in your run as some people choose to have. We have grass and flowers where our chickens roam. Plus bugs, of course.)