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Most other species of edible mushrooms are so particular about their environment that growing them in captivity requires a lot of careful work beyond what most people are willing to attempt. Pleurotus Ostreatus, on the other hand, is such a thriving and eager producer that it can be "copied" in your own home with a simple non-sterile procedure.

You will need:
A container -- a 5 gallon plastic bucket is a good choice
Coffee grounds -- enough to fill the container halfway
Fresh oyster mushrooms, about 2 ounces / 50g or more
some good recipes to make use of the results
A spray bottle.
Notes on source materials:
Your source mushrooms, at least in many American cities, can be bought at a grocery store or supermarket. They must be fresh, not dried, but they don't have to be in perfect condition. In fact, when you can find some that have begun to round the bend just slightly, those are the ones you want. Some Oysters seem not to realize they've been cut and packaged for sale: if you look closely you will find the more exuberant specimens continuing to produce new primordia and even fully-formed stems and caps right off of their own dying bodies. These more virulent examples make excellent starting material for a home culture.

To obtain the necessary volume of coffee grounds, you can either save your own for a while or, better, half-fill your container with recently discarded grounds from a coffee house. If you explain and ask nicely, or just make an excuse about a compost project you're working on, most coffee bars will allow you to take away some of their waste material.

It's preferable to bring home a mass of very fresh grounds like this rather than use your own, because the mass will tend to be properly hydrated, undecomposed, and uncolonized by competitor organisms. Once you establish your Oyster colony you can continue to feed it with leftover grounds from your own kitchen any time.

Planting your own colony is easy
First, make certain the grounds are at a reasonable moisture level. If you can squeeze liquid out of a handful, they're too wet. If a handful, when squeezed into a ball, won't hold together for a second, that is probably too dry. Excess water will breed competitor organisms and restrict the respiration that your oysters need to grow (they expire carbon dioxide, as we do). Insufficient water will stunt or entirely prevent their growth.

Having checked the water content, simply make your container half-full with grounds, then scoop out a hole sufficient to bury your source mushroom in the grounds. Tear your source Oyster (gently) into several pieces and lay them in the hole, then cover lightly with grounds, not too deep. About an inch of grounds covering the mushroom is good.

Care and feeding
What we call a mushroom is only the surface part of the organism -- its reproductive parts, in fact. Before producing actual mushrooms, the organism must grow its main body, known as mycelium, under the surface of its food source.

Maintenance of your Oyster colony is very simple. Keep a lid covering most or all of the container, but not closed tight. Keep the material inside moist by spraying with water now and then. Depending on where you live, water may be needed in the morning and evening, or less than once per day. You will need to experiment with how open or closed the lid is kept, to keep a humid, but not stale, environment in the container. Experiment also with the temperature, by keeping the container in different locations -- some strains of oysters prefer a range of around 55-70°F / 13-21°C; some will thrive in a somewhat cooler or warmer range.

New grounds can be introduced to the container on a regular basis. The colony will still work if you don't, but you will see the original substrate shrink a lot over time as it is consumed by the oysters' metabolism. So feeding the colony is good. But you don't want to feed it so much and so often that its growing mycelium gets too deeply buried. The mycelium is a whitish, stranded, fungal growth that constitutes the underground body of the mushrooms, necessary to their growth before they put up their edible fruiting bodies. After giving the organism an initial week or so to recover from transplant shock and begin growing, you should be able to locate mycelium somewhere in the grounds by gently digging. If you can't find any mycelial growth at all, either the grounds are out of the proper temperature or moisture range, or you're burying the organism too deeply.

Results
The length of time before there are new mushrooms to harvest will depend on climate and temperature. It seems to be a common experience of home Oyster growers to nearly give up on the colony and then, not long after that, take another look to find delicious clusters of gourmet love just waiting to be picked. Perhaps this is due to an effect common to many species of mushroom, in which a slight shock (such as underwatering due to abandonment) actually brings on fruiting -- as long as sufficient mycelium has been generated under the surface first. Typically, though, if you just follow the maintenance suggestions above, you'll have edible results in three to five weeks. The mushroom needs to grow a network of mycelium under the surface, strengthen itself by metabolizing a lot of the raw materials in the coffee-grounds substrate, build a lot of new cells, and finally burst to the surface with new fruiting bodies. This takes some time. Fortunately the burden of ownership is nothing more difficult than daily watering.

Harvesting
Harvest your new mushrooms with a sharp knife, attempting to cleanly sever their above-ground parts without disturbing the surrounding grounds or damaging any immature mushrooms that are nearby. Smaller ones will continue to grow from day to day. For good-tasting and healthy Oysters you'll want to harvest the ones that have reached a fair size but haven't come too close to spreading their gills yet. Try not to allow any of them to fully mature and open up to drop their spores -- this has an inhibiting effect on nearby growth.
Storage and lack thereof
Oyster mushrooms really should not be stored for long. Save them for up to a day or two in a refrigerator, but try to cook and eat them on the same day you harvest them. As much as they seem to thrive and regrow more willingly than other mushrooms, Oysters also have a very short shelf life, beyond which they quickly begin to taste fishy and may even be harmful to your health.

Enjoy!
Oyster mushrooms are delicious when sautéed lightly with other tasty ingredients, as toppings on polenta or pizza, in omelettes or quiche, and in sauces.