So many questions with my new chicks! The current one: How old must they be before I can start feeding them things other than mash/crumbles? For instance, I'd like to give them some clover from the garden (delivered to them--it's too cold yet to go outside). And... does this mean I should feed them grit? And if so, is there a natural version of grit that I can collect from the garden? The closest feed store to me doesn't sell it. Thanks!