Ive always used dry dirt and CC. I bag up bean chaff and use it in bean fields, same with corn and hay chaff. All does well until you get one of those 2" soakers, and the bottom drops out the next day or two. I have NEVFER had good luck with peat. When it gets soaked, and the temps drop, it just freezes into one solid chunk!!! Really interested in how the vermiculite works!!!!