- SMS keeps up to 60% organic stuff even after picking mushrooms.
- Compost from SMS can make soil have more air spaces and grow more plants by 25%.
- Using SMS again helps cut down on trash in dumps and helps farming that reuses things.
- SMS works well as animal bedding that controls wetness and smells.
- Research shows SMS might be good for cleaning up pollution and making energy.
If you’ve ever finished a grow with mushroom grow bags, you’ve likely held the leftover substrate and wondered: is all that material just waste—or a treasure in disguise? Spent Mushroom Substrate (SMS) contains partially broken-down nutrients, fiber, and beneficial microbes—even after the mushrooms are harvested. Rather than throwing it away, you can reuse SMS for garden compost, animal bedding, mulch, or even enzyme extraction. This guide will show you how to stretch the value of your substrate, reducing waste and boosting sustainability in your mushroom cultivation cycle.
What Is Spent Mushroom Substrate and How Is It Made?
Spent mushroom substrate is what's left after mushrooms have been picked. It's made of a mix of organic things based on the kind of mushroom grown—common things are wheat straw, sawdust, soybean hulls, rice bran, coffee grounds, coco coir, gypsum, or even manure. These things are food for the mushroom mycelium as it grows.
The substrate changes in a few ways as mushrooms grow. Fungi break down complex stuff in the substrate to get food, leaving behind organic stuff that's partly broken down. This change makes the substrate "spent," but only for growing more mushrooms—it can still be used for other things.
The Science Behind Mushroom Feeding
Fungi have a special function in the environment as natural decomposers. Different from green plants, mushrooms do not use photosynthesis. Instead, they secrete enzymes such as lignin peroxidase, cellulase, hemicellulase, and xylanases into their growth medium. These enzymes decompose complex plant structures like lignin, cellulose, and hemicellulose into simpler sugars and nutrients that fungi can then take in. The main phases of metabolism include
- Colonization Phase: Mycelium grows into the substrate, breaking down organic materials.
- Vegetative Stage: Nutrient uptake continues, and biomass increases.
- Reproduction: When conditions are suitable, the mycelium develops mushrooms.
Even after this process is complete, the remaining material still contains partially decomposed lignocellulosic material, microbial organisms, organic acids, and structural fibers. This remaining nutrient content and microbial activity allow for impactful mushroom waste recycling.
Is Spent Mushroom Substrate Really ‘Spent’?
Although “spent” suggests “used up,” that’s far from the truth. SMS still retains:
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Roughly 50–60% organic matter, even after a full flush.
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Microbes, fungal hyphae, and partially broken plant fibers that continue to release nutrients slowly over time.
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Structural components (soil-friendly texture, fibrous content) that improve aeration and water retention in garden beds and compost piles.
While SMS isn’t ideal for high-yield fruiting on its own, its residual qualities make it a powerful resource for soil health, garden compost, and secondary uses.
This makes SMS a good thing to use again in farming, gardening, yards, caring for animals, and even research. So think of it as compost material that's partly made or like a sponge full of good stuff for later.
Mushroom Waste Recycling: Why It Matters
Using SMS again to grow more mushrooms is possible but usually doesn't work as well. Because mushrooms take out sugars, proteins, and nutrients a lot at first, the substrate loses much of its food value. Trying again will usually give you smaller, weaker mushrooms and more chance of getting bad molds or bacteria.
But, growers who know more might try to make SMS better again by
- Adding new nutrients – Putting in wheat bran, rice bran, or gypsum.
- Mixing with new substrate material – Often half and half, to lower chances of bad stuff growing.
- Pasteurizing again – This step helps get rid of any bugs and bad things left.
Really, while you can partly reuse it for more mushrooms, it's usually better to find other uses for SMS besides growing mushrooms.
Agricultural Gold: Use Mushroom Substrate Compost in the Garden
One of the most well-known uses for SMS is as a soil amendment and organic fertilizer. Farmers, permaculture practitioners, and home gardeners are increasingly aware of its advantages, which include
- Improved Soil Structure: The fibrous nature of SMS increases soil spaces and air flow, especially in dense or clay-rich soils.
- Enhanced Water Retention: SMS functions like a sponge, assisting plants in getting water during dry periods.
- Increased Microbial Activity: SMS contains many beneficial microbes that speed up nutrient cycling and protect plants from diseases.
- pH Adjustment: Depending on the starting material, SMS can reduce soil acidity or alkalinity, improving nutrient absorption.
Adding SMS to topsoil can increase production for various crops, such as tomatoes, cucumbers, beans, and corn. Research by Phan & Sabaratnam (2012) confirms that the enzymes that break down lignin and nitrogen-containing substances in SMS stimulate beneficial soil life, similar to aged compost but with fungal qualities that aid in disease resistance and healthier root systems. Furthermore, composting SMS with green waste or animal manure can further increase its nutrient content, helping farmers to move towards organic farming methods with fewer external inputs.
Transforming Spent Mushroom Substrate into Bioenergy
The fibrous and sugar-rich composition of SMS makes it very suitable for conversion into bioenergy. Two primary methods can be applied
- Anaerobic Digestion: Microorganisms break down SMS in environments without oxygen to create biogas, a combination of methane and CO₂. The methane can then be utilized for heating, electricity production, or cooking.
- Fermentation: SMS is processed through hydrolysis and fermentation to produce bioethanol, a useful fuel in rural areas and places not connected to the main grid.
Ahlawat et al. (2010) showed that SMS from button and oyster mushrooms can produce biogas amounts similar to those from typical food waste. When SMS is treated beforehand with enzymes or mild chemicals, it breaks down more effectively, making it a possible energy source derived from agricultural waste.
The potential benefits are significant
- Decentralized power sources for farms
- Less dependence on fossil fuels
- Self-contained energy systems within greenhouses
- Economic use of waste at a local level
Investment in biodigester technology and fermentation facilities could transform mushroom waste recycling into a local bioenergy advancement.
How to Use SMS as Mulch or Ground Cover
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Spread a 1-2-inch layer of SMS over soil surfaces (flower beds, vegetable plots, around perennials) to suppress weeds by blocking light.
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Mulched SMS retains moisture well—ideal for dry spells, reducing watering needs.
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Helps buffer soil temperature fluctuations, keeping roots cooler in summer and warmer in colder seasons.
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Use SMS mulch on slopes or raised beds to prevent soil erosion and runoff.
Best Practices:
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Do not press SMS directly against stems or trunks—this can cause moisture-trapping and rot.
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Adjust moisture: SMS naturally holds water, so avoid overwatering beneath mulch.
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Break up or lightly mix SMS into topsoil after a season to avoid compaction.
Community Use: Donate or Share with Gardeners or Farmers
If you don't garden or have a homestead, don’t throw SMS in the trash. Many local growers and groups want mushroom substrate compost because it makes soil fertile and better structured.
Who might want it
- Community gardens
- Urban farms
- School science or farming programs
- Garden groups
- Local compost places or groups that want zero waste
Use online places like Facebook gardening groups, Craigslist, or neighborhood sites like Nextdoor to find people who want it. Say what kind of SMS it is (like oyster, shiitake) and what it's made from if you know, to help gardeners know if it's good for them.
Animal Husbandry and SMS as Bedding
Another new way to use SMS is as animal bedding. It soaks up stuff well and is the right material, so it's good for lowering smells, wetness, and how much farm waste there is.
Great for
- Chicken coops (chickens, quails)
- Goat or sheep pens
- Rabbit cages
- Pig or cow stalls (on top of straw)
SMS bedding soaks up pee and poop well. After it's dirty, it can be composted and used on land as mixed organic stuff. But, make sure the SMS doesn't have mold and isn't dirty with bad things or bugs. Turning the bedding often will help control tiny life and smell.
Sustainable Materials: Biodegradable Packaging & Eco Construction
By considering SMS and mycelium as bio-based resources instead of waste, researchers and environmentally focused startups are creating innovative sustainable products. One promising area is mycelium composites, which are light and shapeable materials created by growing mycelium on agricultural waste, including SMS. These composites can take the place of plastic and foam in
- Protective wrapping
- Shipping boxes
- Building panels
- Furniture interiors
Companies such as Ecovative and MycoWorks have increased the production of biodegradable packaging materials using SMS as a primary ingredient, developing methods that involve carefully managed mycelium growth in molds before drying and finishing. Similarly, SMS can be used to fill wall spaces as natural insulation or compressed into bricks for building projects that produce low emissions. This results in affordable, fire-resistant, water-resistant building materials that have minimal environmental impact.
Hidden Value: Enzymes and Bioactive Compounds in SMS
Even after the mushroom growing cycle is complete, SMS still contains a wealth of valuable biochemical byproducts. Researchers have discovered remaining activity of
- Laccase: Used for removing color from dyes, bleaching paper pulp, and treating wastewater.
- Xylanase: Helps in breaking down hemicelluloses in food, textiles, and cleaning products.
- Protease: Important for pharmaceuticals, waste processing, and certain health supplements.
In addition to enzymes, SMS also contains small amounts of bioactive substances, including antioxidants, phenolics, and polysaccharides, which have potential health benefits. Extracting these biomolecules from SMS can offer
- Affordable enzyme sources for environmentally friendly industries.
- Bio-based additions for animal feed or health supplements.
- Base materials for biodegradable plastics and chemical processes.
Instead of depending on new plant or microbial sources, innovators can obtain useful substances directly from this underutilized biomass.
How to Dispose of Spent Mushroom Substrate Safely
When SMS is fully broken down or can't be used, getting rid of it should be done in a good way to not hurt the environment. Luckily, there are a few eco-friendly choices
- City green bins – Many cities take organic waste for big composting places.
- Bury it – Bury it in garden spots or empty soil areas to make soil better later.
- Home composting – Mix bad SMS with more carbon-based stuff.
- Put it on land – In the country, SMS might be allowed to be put on empty fields or edges to stop soil washing away and add organic stuff (check local rules).
Don't burn SMS, because it can release bad stuff into the air. The idea is to treat it as good stuff, not just trash.
Future Potential for SMS in Bioremediation & Biofuel
As we learn more about sustainable farming, researchers are finding new uses for SMS in industry—mainly in cleaning up pollution and making energy.
Bioremediation
The stuff in SMS from fungi, like laccases and peroxidases, can help clean up bad stuff in dirty soil. These things break down bad waste, like oils, dyes, and metals. Studies are looking at using SMS in filters, landfill walls, or soil cleaning mixes.
Bioenergy Conversion
Because SMS still has plant material, it can be processed to make biogas or biochar. This helps with reusing energy and helps fix farm waste problems.
Future new things might be
- SMS-powered systems making methane or ethanol.
- Making dried SMS into fuel pellets for industry.
- Using it in systems to clean up mining or factory sites.
Mushroom substrate, not really spent at all, might become important in sustainable growth, turning farm leftovers into good resources again.
At Zombie Mushrooms, we think growing mushrooms is just the start—being sustainable begins when the grow bag is empty. Want to grow more than just your crop? Check out our sustainable growing kits, see our best sellers, or start your own closed-loop system today.
Common FAQs About Spent Mushroom Substrate
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Can I reuse SMS to grow mushrooms again?
Yes—but yields are usually much lower. SMS’s nutrient content drops significantly after the first flush. Reusing often works best if mixed with fresh substrate and properly treated (add nutrients, pasteurize, etc.). -
Is SMS safe for composting in home gardens?
Absolutely. When mixed with high-carbon materials (e.g., leaves, straw) and regularly turned, SMS composts effectively and enriches garden soil. -
How long does SMS take to decompose?
Typically between 2 to 6 months depending on moisture, ambient temperature, and how often the pile is turned. -
Can SMS be used as animal bedding?
Yes—it’s absorbent and helps manage odors. However, monitor for molds or pests, and ensure that bedding is clean and safe for the specific animal. After use, SMS bedding can still be composted. -
Is SMS helpful for bioenergy or bioremediation?
It can be. SMS has shown potential for bioenergy (biogas, bioethanol) and pollutant degradation due to its enzyme content. Best results come when pre-treated or processed correctly.
Zombie Mushrooms’ Approach to Responsible SMS Use
At Zombie Mushrooms, our thinking extends beyond just the mushroom itself. Our grow kits are created considering the entire life cycle, including what to do after harvesting is complete. We encourage all of our customers to compost their SMS, or use it to improve their gardens. This is another way we support zero-waste growing practices. Check out our composting guides, environmentally friendly products, and tips for soil improvement to ensure that every component of your grow kit is used effectively.
SMS Applications Table: Quick Reference
| Application | Description | Benefit |
|---|---|---|
| Soil additive | Enhances soil structure & nutrients | Boosts organic crop production |
| Animal feed | Residual proteins and fiber | Lowers feed costs |
| Bioenergy production | Methane and ethanol generation | Renewable off-grid energy |
| Packaging material | Mycelium-based composites | Biodegradable and compostable |
| Construction | Used in eco-bricks and insulation | Lightweight, thermal-efficient |
| Enzyme extraction | Source of industrial-use enzymes | Textile, detergent, or pharma use |
References
- Zhang, R., Wang, Y., & Ma, D. (2014). Utilization of spent mushroom substrate as a feedstock for bioenergy production. Renewable and Sustainable Energy Reviews, 35, 61–69. https://doi.org/10.1016/j.rser.2014.03.032
- Phan, C. W., & Sabaratnam, V. (2012). Potential uses of spent mushroom substrate and its associated lignocellulosic enzymes. Applied Microbiology and Biotechnology, 96(4), 863–873. https://doi.org/10.1007/s00253-012-4428-8
- Ahlawat, O. P., et al. (2010). Bioconversion of spent mushroom substrate to methane. Biomass and Bioenergy, 34(12), 1811–1814. https://doi.org/10.1016/j.biombioe.2010.07.012
- Sharma, S. K., Gautam, R., & Shrivastav, M. (2017). Utilization of spent mushroom substrate in animal feed. J. Animal Health and Production, 5(4), 148–152.
