A Mushroom That Loves Compost

Every mushroom has a favourite food

Mushrooms cannot make their own food from sunlight the way green plants do. Instead they are decomposers — living things that feed by breaking down dead material. Their thread-like body, the mycelium (say my-SEE-lee-um), spreads through its food and slowly digests it.

Different mushrooms like different foods. Oyster mushrooms love fresh straw and wood. The button mushroom is choosier. Its favourite meal is compost — a rich, dark, rotted mix of straw and animal manure. It is a true compost-lover.

Cooking the compost first

You cannot just pile up straw and manure and expect perfect mushrooms. Mushroom farmers prepare the compost in careful stages, and this is grown-up, industrial work done at big farms.

• Phase 1: Straw, manure, and water are mixed into tall piles and turned over many times. Helpful bacteria and other tiny microbes heat the pile up as they work. It can get steaming hot inside.

• Phase 2: The compost is moved into a warm room and pasteurised — heated with hot air for a while. This heating step kills off pests, weeds, and unwanted moulds, leaving clean food that only the button mushroom will enjoy.

Think of it as slowly cooking the perfect meal before the guest arrives. Because it uses heat and heavy machines, only trained adults do this part.

Sending in the spawn

Once the compost has cooled to a safe warmth, the farmer adds the mushroom itself. But you cannot plant a mushroom like a seed. Instead growers use spawn: grains of rye or millet that are already covered in living mycelium.

The spawn is mixed all through the compost. From every grain, the white mycelium creeps outward, exploring and eating, until the whole block is laced with fine white threads. This stage is called the spawn run, and it usually takes a couple of weeks in a warm, dark room.

Full of food, but no mushrooms yet

Here is the strange part. When the spawn run finishes, the compost is packed with healthy mycelium and plenty of food — yet almost no mushrooms appear.

The mycelium is happy just eating and spreading. It has no reason to make mushrooms. To switch it from growing mode into mushroom-making mode, the farmer has to do one more clever thing. In the next lesson, you will discover exactly what that is: the famous casing layer.