From the time of the Greeks and Romans, various fungi have been eaten as a delicacy and the expert can find many varieties growing wild which are equal, if not superior, in flavor to the mushroom (Psalliotta campestris). But there are also a number of poisonous fungi, some deadly. The field mushrooms which appear in profusion in meadows in the moist autumn days are perfectly safe, but the inexperienced townsman would be well advised to make sure first that he is actually picking field mushrooms, because some poisonous fungi are very similar. Cultivated mushrooms are absolutely reliable and a valuable food as well as a delicacy.
Since the war, the production of mushrooms on specialized farms has increased rapidly all over the Western world, in answer to a growing demand. There is a very wide gap between the results achieved by the amateur and the commercial growers, but provided attention is paid to a few essential factors, useful crops can be grown in sheds or cellars, in the greenhouse during the winter and in outdoor beds. The amateur has one big advantage; he can enjoy the flavor of ripe mushrooms taken straight from the soil, the very best way to eat them.
Most commercial growers pick the mushrooms as buttons or cups with the veils unbroken. If they are picked fully open, the delicate pink under-surface often becomes brown and dry before they reach shops, and the flavor suffers.
Mushrooms are grown in a prepared compost which enables the spores to produce cotton-like threads called mycelium which, after a few weeks, emerge on the surface to form pin-heads. These develop in a week to 12 days (according to the temperature), into fully grown mushrooms and successive flushes appear for 10 to 12 weeks or even longer. TheRead more on backyardgardener.com