dust bath materials

[tankernav1]

Mine are about 8 weeks old now. We've let them out of the coop once this week but eventually hope that they will be out a lot once they are full grown. Their bedding is straw right now on top of a concrete pad. There are pine shavings in the nest boxes but obviously they don't use them now---they don't really even go upstairs into the henhouse yet. But should I put a small box with some ashes and/or dirt in it, IN their coop? Do I leave it in all the time? I guess ideally I should get some DE to mix into it too? Hopefully once they are out more later I won't have to feel like they rely on me for total control of their environment!