Perhaps off subject, but a few years ago we bought one of those mushroom tub kits from a garden centre. For some reason or another, the contents and remains where deposited at the bottom of the garden. Every year since, we have had a crop at various times, but we wouldn't fancy eating what pops-up. All yellow mushroom shaped looking clusters.
Tried digging up, putting Jeyes fluid down, but whatever they are, they are winning the battle.