I have used a couple different methods for the grass.
1) I put sawdust in plastic zip-lock bags, then mixed some Rit dye and poured it in the bags. I sealed the bags and then kind of tipped them around until all the saw dust was dyed. I then spread it out on a plastic sheet and dried it under a heat lamp. It worked, but was time consuming and messy.
2) The next time, I just painted the plywood and sprinkled on sawdust while the paint was wet. This was much easier and came out reasonably well.
