Identifying magic mushrooms? information please!?

I have a friend whom is interested in growing mushrooms in the wild. (psilocybin) Today, he went to a cow field and watered it near all the cow feces. Anyways, his question is.. How long will it take? My question is.. how often do these mushrooms end up being the deadly kind? He's never tried picking them. He knows little about this hallucogentic mushroom. But he has done some research. Info please. I'm tired of surfing google with no luck of helpful information.