Shiitakes are also supposed to like coffee grounds. I'm planning to give it a try soon; I got the idea from seeing shiitake kits to which you're supposed to add your daily grounds. (I'd like to try on a larger and more cost-effective scale with spawn and the grounds I can get from the local coffee shop.) A company in my area called BTTR Ventures does a good business growing both oyster & shiitake mushrooms in coffee grounds (at least, I *think* they're still growing mushrooms as well as the grow-your-own kits that are their latest big thing). I've yet to try doing this myself (just came to poke around the forums and see where people recommend ordering spawn), so I don't know how easy it is. From the web, it certainly seems that oysters are the most popular to grow this way, which might indicate that they're the easiest. I could generalize from there and speculate that since shiitakes usually like a wood substrate, other mushrooms that like a wood substrate might also like a coffee ground substrate, but I don't know--might be a good starting idea for research, though.

I must clarify that "mushroom compost" commonly sold in garden centers is spent compost already used to produce a mushroom crop! It is very, very good for vascular plants because the mycelium (which is the real fungus as stated here correctly) has actually improved the availability of nutrients for the plant roots, simply by inhabiting the soil/compost. Once again it is a soil amendment for plants. For growing mushrooms you have to use what the seller of mushroom spawn recommends - straw, wood chips, logs, whatever they say depending on the mushroom species. For a modest crop of button mushrooms good garden soil inoculated with mycelium works just fine. Yes, the medium for commercial growing of the button mushroom is made by thoroughly mixing straw and horse manure in correct proportions and letting it decompose together. Just in case, when the "mushroom seeds" you bought look like grain, that is because they are actual grain that has been pasteurized, inoculated with mycelium and incubated to let it grow, and is now fully colonized by it so it is ready to spread to the next available substrate. I have ornamental mushrooms growing in my backyard :) because I just let them. Have some beautiful dryad saddles' specimens on tree stumps right now in lieu of winter flowers.

I worked at Valdosta State University during the nationwide diaspora of inmates from our insane asylums, in other words, during the time that many of the mentally ill were released with one-way bus tickets to various Florida cities. Frequently, these newly freed men and women would get off the bus in Valdosta to enjoy its Florida-like climate. Sometimes they would camp out in the city's public parks indefinitely. One of them--a Mr. Lark--fancied mushrooms as a culinary delicacy. It was not uncommon to see him gathering mushrooms from the many fairy-rings on the lawns at Valdosta State University. One day--to everyone's horror--he took his mushroom bounty into the first-floor men's room to gourmandize upon them. When the poor man failed to emerge from the public facilities in a reasonable amount of time, a library employee ventured into that restroom to check on him. To everyone's horror, Mr. Lark was discovered prostrate on the floor, deathly ill, with a great issue of blood pouring from one of his orifices. Thankfully, amidst the pandemonium, someone had the presence of mind to dial 911. The paramedics arrived just in the nick of time to rush the Galloping Gourmet to the South Georgia Regional Medical Center, where, fortunately, he was snatched from the Jaws of Death. The moral of this story is be careful what you ingest. As Flannery O'Connor says, "The life you save may be your own."

I don't see why there would be any harm, except that if people use mulch that they want to last forever the mushrooms are a sign of natural decomposition. I use natural wood chips precisely because I want them to compost over time. If I get some tasty or visually interesting mushrooms out of it, all the better. I've checked out all sorts of mushroom hunting guides from the library so that if any wild ones sprout up I'll be ready to id them in the hopes of finding some edible ones.