How mycelium grows, and why a mushroom is only its tip

When we pick a porcini, it feels like that's “the whole mushroom.” In fact, we only see a tiny above-ground part of a huge organism. The fungus itself is the mycelium, hiding in soil or wood and able to spread over an area the size of a room, or even more. Let's look at how it grows and lives.

What mycelium is

Mycelium is a web of the finest white threads, hyphae. They run through the soil, forest litter or rotting wood, soaking up water and nutrients. If you carefully rake aside the litter under a porcini, you can see a whitish “cobweb” — that's the mycelium.

And the mushroom we pick is just a fruiting body. The mycelium sends it up to spread spores, the way an apple tree blossoms for the sake of seeds.

How mycelium grows

It all starts with a spore — a microscopic “seed.” Once it lands in moist, warm soil, it sprouts a thin thread. The threads branch, intertwine and form a mycelium that slowly grows outward in all directions from the center — by roughly 10–30 cm a year.

Many forest mushrooms live in symbiosis with trees: the mycelium wraps around the roots and trades nutrients with the tree (this is called mycorrhiza). That's why porcini grow under oaks and birches, and the slippery jack under pines.

Why mushrooms grow in circles (“fairy rings”)

Sometimes mushrooms appear in a perfect circle — folk tradition calls it a “witch's ring,” known in English as a fairy ring. There's nothing mystical about it: the mycelium grows evenly outward from the center, and fruiting bodies appear along its outer, youngest edge. Year after year the ring gets wider.

Why mushroom spots stay the same

Mycelium lives for years and decades. It survives winter, frost and drought in a dormant state, and when moisture and warmth return, it sends up mushrooms again. That's why experienced foragers return to the same clearings year after year.

And that's also why the mycelium doesn't care whether you cut a mushroom or twist it out — more on that in the article how to pick mushrooms: cut or twist. What does harm it is something else: digging up the forest litter and tearing up moss.

How quickly a mushroom grows from the mycelium — in the piece how fast a mushroom grows and how long it lives. And why mushrooms appear not evenly but in flushes — in the article why mushrooms grow in flushes.

Sources

• “Field Guide to the Fungi of Ukraine” (Kyiv, Naukova Dumka publishing house).
• Mycelium on Wikipedia.
• Fungi in GBIF, the global biodiversity database.