Eating Grass

Question
Hi there,
I just got a bearded collie, and he just loves chewing and eating grass which is fine, but about a month ago i did put some lawn feed down. How do i know when this has disappeared from the lawn?
is it safe for him to eat it. He's thrown up twice since i've had him in 3 weeks, is this normal?

Answer
I would think after a few days the lawn food would have worked its way down to the ground, certainly after a rain.  I am not sure there is a good answer on why many dogs eat so much grass and then throw up.  Twice in 3 weeks shouldn't be a problem unless it was after he cam back in.