Mushrooms are strange little critters, you know. Many people seem to think that they all grow in the dark (not true), that they all get fed manure (grossly false), that most of them, if you see them in your yard, indicate plant disease (wholesale calumny), etc.
While it is true that some mushrooms are associated with plant diseases, most are not. In fact, many are actually necessary for the survival of trees and other plants. This is something that we don't usually get taught in school. Various kinds of fungi get into beneficial relationships with the roots of plants, forming mycorrhizal associations. There are several forms of mycorrhizae, and I do not propose to get overly technical about it here (for one thing, I don't know enough to do it right), but you can find out if you are interested. (I will try to put some pointers into this page.)
Some mushrooms, particularly the mycorrhizal ones that I just
mentioned, are extremely difficult to grow in culture. They don't
want to do much of anything without their little tree-root buddies,
and will just sit on the culture medium, sulking and shirking, like
Bartleby. A few, it turns out, are fickle, and will grow happily if even
tomato roots are to be found lurking in the general area. This turns out
to be really easy to arrange: tomato roots are (relatively) simple to
grow in culture. But even the kinds of mushrooms that will grow mycelium
(mycelium is the growing tissue of the fungus; it is composed
of very thin fibers called hyphae, any one of which is just
about impossible to see with the naked eye, but which are quite visible
en masse) in association with tomato roots are not so easy to fruit.
Getting a nice mat of happy mycelium is one thing, and getting actual
mushrooms is another thing entirely. I am attempting to learn more about
this end of the process, but it's early days yet. When I get anything worth
reporting, I will put it on this page.
(Hah! It is now mid-1999, and I am seriously remiss. Since I
wrote that, I have succeeded in putting many things into
culture, including Blewits, the redoubtable Agaricus augustus,
the so-called "Hen of the Woods" (which is not to be confused
with the so-called "Chicken of the Woods", a nicer mushroom
to be sure but readily available from the better suppliers),
and so on. It turns out to be quite easy to put things into
culture, and not so easy to fruit them. Sigh.)
In the meanwhile, however, there are lots and lots of other mushrooms, some of them truly superior comestibles of more than oriental splendour (if I may be forgiven for misquoting Kipling), that are ridiculously easy to grow. Oyster mushrooms, for example, will eat almost anything. I have seen them growing on old newspapers, old coffeegrounds, ... how easy can it get?
The trick (of course there's a trick, otherwise most gardeners would be doing this already) is that you have to learn a bit of sterile-culture technique, which is slightly tedious. You also have to have access to a pressure-cooker, because you need to be able to sterilize things, and just boiling them won't do it. (If I can, I will put in a link to a page about the recent work in which some people revived bacterial endospores that were estimated to be 40 million years old or so. Endospores are... how shall I say this?...quite refractory.)
Once you have a reasonably sterile medium (please note: the term 'sterile' really is relative!), you have to get some mushroom tissue onto it without introducing other contaminants. The usual way to do this is to create a vaguely sterile working environment and then rip the mushroom open to expose a fresh and reasonably sterile surface. Then you take a sterile implement and dig out a bit of tissue, which you plop onto your medium. If all goes well, this tissue will proceed to grow new mycelium. Of course, you have to maintain sterility throughout the process, so you seal the medium up (in a petri dish or a flask) to keep things out of it.
In practice, occasional contamination is unavoidable. Depending upon how good your technique is and how good your working environment is, you get some percentage of contamination, and you live with that. The usual way around it is redundancy. (Let me say that again: redundancy.) You can take more than one sample from a given mushroom, for example. I typically put three or four bits on one petri dish. You can also use more than one dish. I typically try for two, three if I am particularly anxious about getting a culture.
Once you have a clean culture, you make copies of it by digging out bits of the culture medium with mycelium attached and putting those bits onto new dishes. When you have three or four clean dishes of a given culture, you can relax a bit. You hope.
This still doesn't get you any mushrooms, however. For that, you must go through a few more stages. I will address those when I get a few more moments to write on this page. Meanwhile, I can suggest a book or two for those of you who are particularly interested.
Growing Gourmet and Medicinal Mushrooms, by Paul Stamets, is a very good start. Stamets is knowledgeable, has grown many different kinds of mushrooms, and is understandable. (I would like to have been able to copyedit his text, but...)
If you want to know a whole lot about contaminants, an earlier book may prove useful. The Mushroom Cultivator, by Paul Stamets and Jeff Chilton, has an extensive section on the characteristics of many contaminants that one runs into when growing mushrooms. Oddly (at least, it seems odd to me), many growers don't seem to like that section. They seem to think that it is excessive. Me, I think it's great. If I get garbage growing in my cultures, I would much rather be able to tell what it is. (Sometimes it is possible to rescue a contaminated culture; sometimes it is extremely difficult. If I do not have to throw a culture out, I'd rather not do so.) This book, by the way, is just riddled with typos and errors. I grit my teeth.
There are lots of decent mycological pages on the Web; I've mentioned a few on my page of links, and you can use your favorite search engine to find more.