What kind of shroom? If it's a primary decomposer like oysters or something, then the easiest way is to just innoculate more dowels or woodchips. That is as simple as boiling the woodchips or dowels, letting them cool, then mixing them with some innoculant into a clean bag, tub or box. No sterilization necessary. Even simpler is to use cardboard instead of woodchips/dowels.
If it is not a p. decomposer then I think the best way to test viability is using any sterile medium. This could be agar or grain. I prefer popcorn instead of wild birdseed because I have had better luck with the moisture content being right.
