Mushroom compost bought from stores is a false ideal. Its called mushroom compost cus in theory you can a mushroom out of it, but it reality is a tiny ammount of low quality compost mixed out with peat and some cheapo ammendments. That being said mushroom compost will work in lu of better soils in a pinch. But dont think for a sec that its good compost. All store bought compost is crap, you gotta make yer own if you want the good good