Mycelium Takes Over

Meet the white web

Look closely at your grow block. That white, cottony fuzz spreading through it is not mould and it is not fluff. It is mycelium (say it "my-SEE-lee-um"), and it is the real body of the fungus.

Remember the single thread, the hypha, from the last lesson? Mycelium is what you get when millions of those threads branch, cross, and weave together into a living network. The mushroom itself is only a small part that appears later. The mycelium is the main organism, hidden inside the block.

Eating without a mouth

Mycelium has a surprising job: it eats. But a fungus has no mouth and no stomach, so it eats in reverse.

The threads release special chemicals called enzymes into the block. Enzymes break tough food, like straw, sawdust, or wood, into tiny pieces the fungus can soak up. So the mycelium digests its meal outside its body, then drinks the goodness back in.

This is why fungi matter so much in nature. Out in a forest, mycelium breaks down fallen logs and dead leaves and returns their nutrients to the soil. Fungi are the planet's great recyclers.

Colonising the block

When mycelium spreads through fresh food, growers call it colonising. The threads march outward in every direction, claiming new territory as they eat.

Oyster mushrooms, the kind in most starter kits, are fast. From a spawned block, their mycelium can take over the whole thing in about three to four weeks. As it goes, the block turns from patchy to solid, snowy white. A fully colonised block even feels firm, because the threads bind everything together like living glue.

You can help by giving the block what the mycelium likes:

• A warm, room-temperature spot

• Not too much bright light yet

• Being left alone, without poking or opening it early

Storing up energy

While the mycelium colonises, it is not just spreading. It is also storing up energy from all that food. It cannot make a mushroom until it has eaten enough and claimed enough space.

Think of it like filling a fuel tank. A mushroom is expensive to build, so the fungus waits until its network is strong and its tank is full. Only then is it ready for the next big change.

Sometimes a block grows a patch that looks a bit different in colour or smell. That can be another mould moving in. If a grown-up thinks a block smells sour or looks slimy and off, it is safest to set it aside. Healthy oyster mycelium is white and smells pleasantly earthy or mushroomy.

In the next lesson, the full block gets a wake-up signal, and the first baby mushrooms appear.