Everything you need to know about mycelium: storage, harvesting, and varieties to grow

In this article 8

What is commonly called a “mushroom” is actually the fruiting body: the reproductive organ, equivalent to an apple on an apple tree. The organism itself is the mycelium, a network of white filaments that colonizes the substrate, feeds on it, and sometimes lives there for years.

Mycelium is therefore what we buy, store, and establish. Understanding what it is, the forms it takes, and what kills it prevents most failures.

What mycelium is

Mycelium consists of hyphae: microscopic filaments that grow from their tips, branch, and fuse together. As they spread, they secrete enzymes that break down the surrounding material and absorb the released nutrients.

Cluster of oyster mushrooms growing in tiers on a dead beech trunk in an autumn woodland — What we see is only the fruit. The organism itself has lived in the wood for years and will continue living there after harvest.

Two implications that explain almost everything about how to manage a culture:

It is a living organism, not a seed. It breathes continuously, does not go dormant, and cannot tolerate either complete desiccation or freezing. A seed forgotten in a drawer for three years may still germinate; mycelium will not.
It fruits in response to a signal, not maturity. The transition to fruiting is triggered by a change in conditions—light, fresh air, humidity, or a drop in temperature. Perfectly established mycelium may never produce anything if that signal never comes.

The key most beginners miss

The conditions for colonization and fruiting are opposite. Darkness, warmth, and little air for colonization; indirect light, coolness, and ventilation for fruiting. This explains why most substrates that turn completely white never produce anything.

Available forms

Cereal grains connected by white mycelium through the walls of a sealed jar. — Grain mycelium is another form of inoculum: the white network develops between the grains. It differs from the liquid mycelium offered in stores.

Form	Principle	What it enables
Colonized substrate block	Already colonized substrate, ready to fruit	Fast results, but only one to three flushes before exhaustion
Mycelium on grain	Grown on rye, millet, or corn.	Inoculate your own substrates. Requires strict cleanliness.
Liquid mycelium	A living strain in a sterile suspension	Long-term establishment in an ecosystem rather than a single harvest. This is the form we offer.
Spores	The mushroom equivalent of seeds	For experienced experimenters only: unpredictable genetics and a high risk of contamination

The fundamental difference between a block and liquid mycelium is not a matter of convenience but of purpose: the former produces and then becomes exhausted, while the latter becomes established. A properly inoculated log or forest floor can produce for years.

Storing your mycelium

This is the most frequently asked question, and the most misunderstood: mycelium is alive, so it ages.

In the refrigerator, between 2 and 6 °C, in its original packaging and protected from light. The cold slows its metabolism without stopping it.
Do not let it dry out. Unlike a seed, it does not survive desiccation.
Realistic shelf life — a few weeks to three months for fresh grain spawn or a block, and longer for properly stored liquid mycelium. In all cases, the sooner you use it, the greater its vigor.
Do not leave it in a car or near a heat source — above 35 °C, most strains weaken rapidly.

Never freeze it

Ice crystals rupture cell walls: the mycelium loses its vigor, often permanently. Cryopreservation is used in laboratories, but it requires cryoprotectants and specialized equipment.

How to tell whether it is still good

Good sign — bright white or slightly cream-colored, with a forest-floor or fresh mushroom smell and a cottony or filamentous appearance.
Bad sign — green, black, or pinkish spots; a sour or rotten smell; or a slimy appearance. These indicate contamination: the batch is lost.
Neutral sign — a yellowish tint or amber droplets on the surface of mycelium on grain are common and generally harmless.

Varieties, ranked by accessibility

Getting started — saprophytes

They break down dead organic matter: no partner tree is needed, indoor cultivation is possible, and the first harvests can come within a few weeks to a few months.

Oyster mushroom — the gateway mushroom. Forgiving, fast-growing, and grows on straw, cardboard, coffee grounds, or logs.
Shiitake — on oak or beech logs. Slower, but one log produces for several years.
Button mushroom and its brown variety — on pasteurized compost, in complete darkness.
Black mushroom — highly productive on wood, excellent when dried.

SemiSauvage liquid oyster mushroom mycelium

In our shop Oyster mushroom mycelium (Pleurotus ostreatus) Living strain in liquid mycelium · the most forgiving variety for beginners · €17.96

Intermediate

The fairy ring mushroom does not require any tree: a meadow or lightly trafficked clearing is sufficient, and it fruits from the first or second year. It is the best compromise between ease and outdoor cultivation.

For a long-term project — mycorrhizal mushrooms

They live in symbiosis with living trees and cannot fruit without a plant partner: chanterelle, black trumpet, hedgehog mushroom, porcini, morels and truffles.

Allow three to ten years depending on the species. See Growing forest mushrooms and Growing rare mushrooms.

Harvest without depleting the mycelium

Harvesting is not the end: the mycelium remains alive in the substrate and will produce again if it is not damaged.

Harvest before the cap flattens completely, when the edges are still slightly curled under. Beyond that point, the massive release of spores unnecessarily exhausts the substrate.
Gently twist and pull at the base rather than cutting. A stump left in place rots and becomes an entry point for contaminants.
Harvest the entire flush, including the small specimens: they will not grow any larger once the flush is over, and their presence delays the next one.
Between flushes, rehydrate the substrate and let it rest for a few days in the dark. Allow one to two weeks between each flush.
In the wild, cover the hole with leaf litter and leave a few specimens to mature in place.

David's advice

An exhausted substrate is not waste: incorporated into compost or used as mulch, it continues to nourish soil life. The residual mycelium sometimes even continues its decomposition work there.

Harvesting a cluster of oyster mushrooms held at its base, with another hand supporting the grow bag. — Supporting the substrate and grasping the cluster near its base makes it possible to handle oyster mushrooms without crushing their caps.

What kills mycelium

Chlorine. Tap water alone can compromise a preparation. Use mineral water, or let the water stand in the open air for 24 hours so the chlorine evaporates.
Preservatives. The logic is the same: a commercial syrup containing preservatives is literally an antifungal. Hence the requirement for preservative-free syrup when preparing liquid mycelium.
Freezing. Fatal in most cases.
Excessive heat. Above 35 °C, vigor declines rapidly.
Contamination. Green or black molds, bacteria. They result from unclean handling, an improperly pasteurized substrate, or excess moisture. Wash your hands, limit openings, and work in a draft-free place.
Fertilizers and fungicides near an outdoor inoculation. A fungicide cannot distinguish your strain from a pathogen.

Frequently asked questions

Can you multiply your own mycelium?

Yes, by taking a fragment of well-colonized substrate to inoculate a new batch. The limitation is senescence: after repeated transfers, a strain loses its vigor and ability to fruit. Four or five generations is a reasonable rule of thumb before starting again from a fresh strain.

Can mycelium escape into the garden?

Saprophytic species can indeed colonize surrounding dead wood — this is more of a benefit. Mycorrhizal species, on the other hand, remain associated with their partner trees. None of these species is invasive in the sense in which the term is used for a plant.

Why is my substrate white without producing anything?

Because the fruiting signal has not been given. Open it to indirect light, humidify the air, ventilate, and lower the temperature slightly. For shiitake on a log, soaking it in cold water serves as a trigger.

How long does established mycelium live?

A kit block, a few months. An inoculated log, three to six years. A successful outdoor establishment, potentially decades — as long as the source of organic matter or the partner tree remains.

Should the substrate be sterilized or pasteurized?

Pasteurization — one hour in water at 70–80 °C — is sufficient for straw and suitable for oyster mushrooms: it eliminates competitors without killing all the life in the substrate. Complete sterilization is reserved for nutrient-rich substrates, which are more susceptible to contamination.

Key points

The essentials in three lines

Mycelium is a living organism: it breathes, ages, and cannot be stored like a seed. Refrigerate it between 2 and 6 °C, never freeze it, and use it promptly. Then remember that colonization and fruiting require opposite conditions — this explains why most white substrates produce nothing.

Going further

Discover our mushroom and mycelium collection — fifteen living strains, from oyster mushrooms for beginners to Périgord truffles.