Q: I know that mushrooms are a fungus. Is it a good idea to take mushrooms that grow in my yard and put them into the compost pile? It seems logical that the mushrooms would be good organic matter.
A: Your intuition is exactly correct. Mushrooms are nothing but organic tissue produced by underground fungi. They are mostly water, and so will dry to almost nothing, but grass clippings do the same thing. There is no harm in composting mushrooms; they may help with the composting process as they innoculate the pile with fungal spores.