A mushroom develops in two stages: a vegetative phase when it grows and decomposes organic matter, and a fruiting phase, when mushrooms (fruiting bodies) are produced. The cool, moist environment in woodlands is ideal for the growth and development of mushrooms and some species can be cultivated under these conditions. The strategy in cultivating mushrooms is to introduce a desirable species onto a growing medium and promote its growth, so that eventually fruiting bodies are formed.

The process of growing mushrooms can be divided into four steps:

1. Acquiring and maintaining a culture of mushroom tissue, (called mycelium), of the species intended for cultivation. A tissue culture is somewhat like a cutting of a plant. Some growers start with mushroom spores, which are more like the seeds of a plant.
2. Using a bit of the tissue culture to begin some mushroom spawn, (a kind of mushroom starter), which is usually grown on a small quantity of sterilized grain or sawdust.
3. Using the spawn to introduce mushroom mycelium into an organic material or substrate, chosen to support the formation of fruiting bodies.
4. Getting the fruiting bodies to form and grow once the substrate has been completely colonised by mushroom mycelium.

If you buy a mushroom kit, you are generally starting at step four. The commercial mushroom grower has already completed the earlier steps and provided you with the mushroom culture ready to form fruiting bodies. You will need to provide an appropriate environment, usually cool and moist. Getting the mushrooms to form can be easy or difficult depending on the species selected. The genus Pleurotus (various species/variants of Oyster Mushroom) and Hypsizygus (Elm Mushroom) are among the easiest to fruit. Grifola frondosa (Hen of the Woods or Maitake) and the genus Morchella (Morels) are among the most difficult; Shiitake falls somewhere in the middle.

It is also possible to start at step three, by purchasing the starter spawn from a supplier and using that to introduce the growing mushroom into an organic material that you have prepared yourself. There are a variety of possible substrates: straw, compost, logs, wood chips and sawdust, but people have also used materials like newspaper, cardboard, sterilized grain, coffee grounds, etc. depending on the mushroom species to be cultivated.

In general, there are three broad groups of cultivated mushrooms: those that prefer to grow on compost, (humus-inhabiting fungi), those that naturally grow on woody material, (wood-inhabiting fungi) and those which are mycorrhizal, forming a symbiotic relationship with the roots of trees. Mushrooms of the genus Agaricus, Blewits, Stropharia rugoso-annulata (Wine Cap Mushroom) and Coprinus comatus (Shaggy Ink Cap) fall into the first group, growing readily on compost, but they will also grow on straw. Oyster Mushrooms, Shiitake, Maitake, Enokitake, Elm Mushroom, Laetiporus sulphureus (Chicken of the Woods), Sparassis crispa (Cauliflower Fungus) and Hericium erinaceus (Lions Mane) all prefer woody material such as sawdust, wood chips or logs. The third group are of course the truffles, which prefer oak or beech trees in the wild; these are commercially available as truffle trees (inoculated hazel or oak).

Thanks to Clifford Davy of Forest Foragers.