What to do with the substrate after cultivation? 

After several growing cycles, the substrate used for mushroom production becomes less productive. Rather than considering it waste, it can be valorized as "champost" (mushroom substrate compost), thus fitting into a circular economy approach: "nothing is lost, everything is transformed."

When is a substrate considered "finished"?

A substrate is generally considered exhausted when it shows the following signs:

• Significant decrease in production: mushroom yield decreases noticeably. Growing spaces are generally limited, so after 1, 2, or 3 harvests, the bags are usually discarded. This notably depends on the mushroom varieties cultivated, the growing conditions, and the space the grower has available. It is sometimes possible to continue for a fourth, fifth, or even sixth harvest, but it is generally not worth it.
• Contamination: appearance of molds or bacteria, which can then spread more easily to other blocks and reduce productivity.
• Infestation by insects: presence of fungus gnats or other pests. Nobody likes having fly larvae in their mushrooms, right?

These indicators suggest that it is time to replace the substrate and consider its reuse.

Why is used substrate so valuable?

Unlike other organic materials, the mycelial substrate has been partially broken down by fungal enzymes. The mycelium excels at degrading complex materials like cellulose, lignin, or wood fibers, making nutrients more accessible to plants.

This transformation process improves:

• soil structure, by binding particles and increasing water retention;
• microbial biodiversity, by promoting bacterial and fungal life;
• plant protection, some fungal species producing natural antifungal compounds that inhibit soil pathogens.

A recent study by Khalil et al. (2024) showed that mushroom compost improves vegetable growth and significantly reduces root disease pressure. 

How to valorize spent substrate?

Spent substrate from lignicolous mushroom cultivation (shiitake, oyster mushrooms, lion’s mane…) is a resource rich in organic matter partially decomposed by fungal enzymes. Far from being mere waste, it can have a useful second life in many contexts, thus fitting into a circular economy approach.

🌱 1. Organic amendment and fertilization

Straw-, sawdust-, wheat bran-, or wood chip-based substrates are already pre-digested by the mycelium, making them more easily assimilated by soil microfauna.

• Improves soil structure: better water retention, aeration, reduced compaction.
• Stimulates microbial life: residual mycelium + organic matter = living soil.
• Use: directly as mulch or incorporated into the soil after 2-3 months of maturation.

⚠️ Warning: using fresh substrate too early can cause nitrogen competition. It is recommended to let it mature or partially compost before use.

🌾 2. Market gardening and permaculture

In intensive organic matter systems like permaculture mounds, the fungal substrate is a valuable ally:

• Use in lasagna beds, mounds, or mulching around vegetables (e.g., tomatoes, squash).
• Base for seedlings or plantings, after additional composting.
• Stimulates soil resilience thanks to the microbial diversity it provides.

🍄 3. Reinoculation for secondary cultivation

A so-called “exhausted” mycelial substrate can still produce fruits, especially if rehydrated and placed in good conditions:

• Oyster mushrooms: often able to fruit 1 to 2 more times after fruiting in controlled rooms.
• Growing secondary species that are less demanding (Stropharia, Coprinellus...).

This practice is common in low-cost systems or urban farms

🐄 4. Bedding or animal feed (experimental)

Some farmers use the substrate as dry bedding for poultry, goats, or cattle. It absorbs moisture and improves comfort.

Research (notably in Asia) has also explored its use as enriched fodder, but this requires strict controls (digestibility, toxicity, spore residues).

🔥 5. Combustion or methanization

Rich in cellulose and lignin, the substrate can be valorized energetically:

• Methanization after pretreatment, with biogas production.
• Pellets or briquettes for heating, after drying and compression (performance varies depending on moisture).

🧪 6. Extraction of molecules or enzymes

Fungal residues still contain lignolytic enzymes, such as laccase or peroxidase. These molecules have potential for:

• Bioremediation (pollutant degradation).
• Industrial enzyme production (paper, textile, food...).

🦗 7. Breeding decomposer insects (earthworms, soldier flies, beetles...)

The used substrate of wood-growing mushrooms is an excellent base for breeding decomposer insects. These insects transform organic matter into proteins, fertilizer, or quality humus, while fitting into a natural biological valorization loop.

🐛 Earthworms (Eisenia fetida, Eisenia andrei)

• Ideal processors for partially composted or mature substrates.

• Their slow but thorough action produces a stable and nutrient-rich vermicompost.

• Ideal for gardeners, communities, or small-scale composting systems.

🐛 Black soldier fly larvae (Hermetia illucens)

• Very effective at quickly digesting moist substrates rich in decomposed or myceliated plant materials.

• Produce a protein biomass usable in animal feed (poultry, fish).

• The digestion residue (frass) is an excellent natural fertilizer.

• Recommended in agricultural contexts or semi-industrial insect farming.

🐛 Saproxylophagous beetles (Tenebrio molitor, Dermestes spp.)

• Prefer dry substrates rich in cellulose (sawdust, bran, straw).

• The mealworm (Tenebrio) is often raised for the production of edible proteins (human or animal).

• Less sensitive to fungal contamination than other species.

📊 Comparison by substrate type

Champost and the circular economy

In a context where sustainable resource management becomes a priority, the reuse of spent mushroom substrate fully fits within a circular economy logic. This approach aims to reduce waste, extend the life of materials, and recreate value at every stage of the production cycle.

src: https://www.mdpi.com/2313-4321/9/4/58

♻️ Give a second life to a by-product

Rather than considering the used substrate as bulky waste, it is requalified as a useful resource. Transformed into organic amendment, mulch, or a compost component, it returns to the earth and continues to nourish life.

This principle of biological upcycling closes the loop between production, processing, and regeneration.

🌍 Reduce waste and emissions

• Avoiding landfilling or incineration of the substrate helps limit CO₂ and methane emissions.
• Reusing these organic materials locally reduces transport and disposal costs.
• Organic valorization avoids the use of chemical fertilizers, energy-intensive to produce and responsible for soil pollution.

🌾 Supporting local and sustainable agriculture

By distributing used substrate to local market gardeners, farmers, or gardeners, a virtuous territorial dynamic is supported:

• Soils naturally enrich in organic matter.
• Agricultural yields can improve without synthetic inputs.
• Cooperations between producers (mushrooms, vegetables, composters...) promote the resilience of local sectors.

🌱 An educational and civic opportunity

Mushroom compost is also an educational tool to raise awareness of ecological transition issues. It concretely illustrates that agricultural "waste" can become fertile resources, and that ecology and productivity can go hand in hand.

Communities, schools, or associations can take it up to create projects of urban agriculture, permaculture, or collective composting.

🔗 Towards a local valorization loop

The establishment of partnerships between mushroom producers, farmers, composting platforms, breeders, or local authorities allows building a true circular chain:

• The used substrate becomes a product in its own right.
• The resource remains in the territory, creating local jobs and reducing the import of amendments.
• Each actor benefits from an optimized and sustainable flow.

In summary: integrating used substrate into a circular economy circuit means turning a constraint into an opportunity, for the earth, for humans, and for the environment. It makes the mushroom a soil actor... and an agent of change.

Where to get used substrate?

At La Mycosphère, we offer used substrates from our cultures.

These substrates are available for gardeners, farmers, or anyone wishing to valorize them in an ecological way.

À propos de l’auteur

Quentin Gobert
Fondateur de La Mycosphère

Passionate about the fungal world and a committed entrepreneur, Quentin shares his knowledge and expertise through articles and consulting. With the Mycosphere, he aims to raise public awareness about the importance of mushrooms in our ecosystems and to promote innovative solutions for a sustainable future.

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