I've got 10 weekers now and they are getting starter/grower crumbles along with a handful of scratch now and then and the occasional fruit/veggie/oatmeal treat. They have access to a dirt floor coop.
If you are giving them scratch they should have grit, unless they are able to get enough sand, rocks/gravel etc thier crop will get blocked because they will not be able to PROCESS the other food you are giving them.