Cultivating your own mushrooms ensures that you'll always have a fresh supply of your favourite varieties, free of additives, and it allows you to experiment with some exotic species. It's a more complicated process than growing plants, though, and involves three distinct stages. The second stage, spawning, depends on a healthy supply of mycelium grown in a petri dish. If the spawn remains healthy, you can fruit it in a bed of compost or wood chips. Sterile conditions are required for all three stages, and it's a good idea to invest in an air purifier.
Create a sterile working space by wiping your work table with disinfectant and running a high efficiency particulate (HEPA) air filter in the room. Even a slight contamination of random mould or fungus will ruin your spawn.
Mix 28.4 g (1 oz) of agar medium with 1/2 litre (1/2 quart) of water in a flask with a tight lid. Sterilise the flask in a pressure cooker for 45 minutes, then let the solution cool for two hours.
Sterilise your hands, then pour the solution into five or 10 petri dishes. You only need one good culture to make spawn, but if you make several, you'll have a better chance of having a good one.
Cut spores from the underside of the cap of a fresh mushroom with a sterile scalpel, or mycelium from the inner part of the stalk. Cut pieces about the size of the tip of your finger and drop one into each petri dish. Place lids on the dishes and wrap electrical tape around the edges to seal them, then store them in a container that has been disinfected.
Check the dishes frequently and discard any that have been contaminated. Pure mycelium is white and fibrous, while contamination by mould or other fungi will appear as a dark bubble. Spawn the mycelium when it has covered the bottom of the dish, which could take anywhere from one to three weeks.
Fill five 1 litre (1 quart) mason jars with 0.57 litres (1/2 pint) of wheat, rye or millet and add 237 ml (1 cup) of water and 1/3 tsp gypsum to each. Sterilise the jars in a pressure cooker for an hour, then allow them to cool for an hour. Wearing sterile rubber gloves, remove the jars from the cooker and shake each one vigorously to loosen the grain. Allow them to cool to 21.1 degrees Celsius (70 degrees Fahrenheit).
Sterilise a 9 mm (3/8 inch) drill bit and drill a hole in the top of each jar. Cover the hole with electrical tape.
Pour 1 litre (1 quart) of water into the cup of a stainless steel blender and sterilise the cup in the pressure cooker for 45 minutes. Let it cool to 23.9 degrees Celsius (75 degrees Fahrenheit). Pour in the contents of the petri dish that has the best-looking culture and blend the mixture with three short bursts, lasting one or two seconds each.
Draw the mixture into a sterile syringe and spray 9.45 g (1/3 oz) into each mason jar through the hole in the top. Replace the electrical tape after you spray.
Incubate the jars in a sterile cabinet at 23.9 degrees Celsius (75 degrees Fahrenheit). The spawn is complete when the grain has turned a uniform white colour.
You can grow the mushrooms by spreading the grain spawn on sterile compost or wood chips, or you can use it to make sawdust spawn to inoculate outdoor garden beds. Some mushroom species may require higher or lower temperatures to spawn.
The sterile conditions for growing mushroom spawn are not easy to create. A simple laboratory to enable cultivation can easily cost thousands of pounds and you may have to try several times before being successful. You can also buy spawn to inoculate your own mushroom beds.