Can you reuse spent mushroom substrate?

For every kilogram of mushrooms produced, there will be 5 – 6 kg of by-product[1]. As worldwide, around 12.74 million tons (MT) of mushrooms were consumed (2018)[2] we will end up with 38.22 to 63.7 million tons of spent mushroom substrate each year.

How do you deal with that?

To answer this question, I will talk first about what spent mushroom substrate is, then what you can use it for, and finally, show you how to apply it to your mushroom farm.

Sounds good? Then let’s start!

What is spent mushroom substrate?

Spent mushroom substrate (SMS) is the leftover substrate (compost in case of button mushroom) after the termination of the entire mushroom crop, after which mushroom cultivation becomes unremunerative[3].

The term „spent mushroom compost” (SMC) is used interchangeably with “spent mushroom substrate” (SMS)[4]. During my article, I will use the term spent mushroom substrate or the abbreviation SMS.

The top 3 mushroom producers are China 5,150,000; Italy 785,000; USA produces 388,450 MT of mushrooms[5] (all numbers are metric tons).

What to do with spent mushroom substrate?

There are many exciting areas SMS can be applied[6].

  • Bioremediation (Air, water, soil, pesticides)
  • Crop production (greenhouse crops, field crops, general soil amendment/fertilizer, nursery, and landscape)
  • Cultivation of mushrooms (casing material, cultivation substrate)
  • Food for animals and fish
  • Disease management
  • Renewable energy
  • Enzyme recovery (e.g. α-Amylase, Laccase, Xylanase)[7]

For the purpose of this article, I will only focus on the cultivation of mushrooms. I will show you how to use it as a substrate source.

But there is no free lunch.

SMS possesses some agronomic disadvantages to its possible further use in horticulture or agriculture. Principally, it has high salt content, and if incorporated into land at high application rates or utilized in too high a quantity in a growing medium, it inhibits plant growth[8].

A study on the mean composition of SMC from Ireland, the Netherlands, and the United States reported that the content of nitrogen is considerably high; however, the amount of readily available nitrogen in the form of nitrate and ammonium is small.

In contrast to nitrogen, phosphorus is water-soluble, is readily available to plants, and is the main determining factor in applying SMC to land.

With that in mind, we can now think about how to reuse mushroom substrate.

How to prepare spent mushroom substrate

Before you can use SMS, you have to prepare it. But what is the right way to do it?

During my research, I found the following process, which is used for Pleurotus spp.:

Process for Pleurotus spp.

  1. Mechanical shredding
  2. Drying
  3. Adding substrate
  4. Adding supplements
  5. Mixing
  6. Bagging
  7. Sterilization
  8. Cooling
  9. Inoculation
  10. Incubation
  11. Fruiting

If you are growing Agaricus and you want to use SMS as part of your casing layer than this process can guide you:

Process for Agaricus spp.[9]

  1. Mechanical shredding
  2. Piling for 14 weeks
  3. Turnover every 14 days for 10 weeks
  4. Adding substrate
  5. Mixing

Is it possible to grow mushrooms on spent substrate?

By now, you should know the answer. Absolutely. SMS is considered a nutrient-rich source for mushrooms[10].

If so, what results can you expect if you are using SMS?

In the following section, I will show you examples from several studies obtained from applying spent mushroom substrate. We first take a look at Pleurotus spp. and then Agaricus spp.

Growing Pleurotus on spent mushroom substrate

In the first study done back in 2012, the researcher mixed spent mushroom substrate (from Pleurotus) with wheat straw (1:1), calcium sulfate, and calcium carbonate. They pasteurized the mixture at 60-65°C for 8 hours and applied either Calprozime®, Champfood®, or Promycel® 600 to it.

As the results (Fig. 1) are showing, adding one of the three supplements to the mixture helped to increase not only the overall biological efficiency but the biological efficiency for the 1st flush.

Second, the biological efficiency of all three mixtures was similar to commercial control. That’s not bad at all for reusing your current substrate.

Influence of different supplements added to spent mushroom substrate on the biological efficiency of Pleurotus ostreatus

Figure 1: Influence of different supplements added to spent mushroom substrate on the biological efficiency of Pleurotus ostreatus[11]

In the next study, the author used spent shiitake mushroom substrate to cultivate Pleurotus sajor-caju (actually Lentinula sajor-caju). 

While doing the research, the author found out that “85% of the original hemicellulose, 44% of the original cellulose and 77% of the original lignin was not consumed during the production of a full crop (78% biological efficiency) of shiitake[12]”.

With these numbers in mind, we now can understand why reusing spent mushroom substrate is a good strategy. To work, you don’t need that much additional substrate or supplementation.

For this study, the author used 14,528 g SMS (45 % moisture), 785 g white millet (12 % moisture), 785 g wheat bran (12 % moisture). He then added soybean (12 % or 24 %) and or calcium carbonate (1 % or 2 %) to the mixture.

The results are speaking for themselves (Fig. 2). To get the most out of your SMS, you have to add supplements to it. The best result was achieved by adding 12 % soybean and 1 % calcium carbonate.

Effect of different substrate types of spent Shiitake substrate mixture

Figure 2: Effect of different substrate types of spent Shiitake substrate mixture with white millet and wheat bran supplemented with soybean and calcium carbonate on the biological efficiency of Pleurotus sajor-caju[13]

Growing Agaricus on spent mushroom substrate

The following study used SMS as part of the casing layer[14]. This layer is needed to initiate pinhead formation.

The authors mixed the SMS either with vermicompost, sunflower seed hulls, peat Sphagnum peat moss, or brewery residues.

According to figure 3, the best result was achieved by adding sunflower seed hulls and brewery residues (70:30) to the spent mushroom substrate.

Effect of Pleurotus spent mushroom substrate with different amendments on the biological efficiency of Agaricus blazei

Figure 3: Effect of Pleurotus spent mushroom substrate with different amendments on the biological efficiency of Agaricus blazei[15]

Many studies “have shown that it is possible to produce A. bisporus on NCS and that yields may be equal to or exceed those on traditional Phase II compost[16].”

The authors continue, “however, to date, A. bisporus is not produced commercially on NCS. The economic feasibility of producing A. bisporus on sterilized NCS remains to be determined, and the most economical and productive processes for producing mushrooms on this substrate are still evolving.”

What do the authors mean by NCS? NCS stands for non-composted substrate.

In their study, the authors used the following formula for the casing layer:

Oak sawdust (28 %), millet (29 %), rye (8 %), peat (8 %), ground alfalfa (4 %), ground soybean (4 %), wheat bran (9 %), and CaCO3 (10 %).

Supplements: Target® (T) or soybean meal (SM)

But they varied not only the type of the substrate but also the time of supplementation. To understand the next chart (Fig. 4) here is the legend:

Substrate: SMC (S), NCS (N); PIIC (P)

Timing: Spawning (S), Casing (C)

Supplement: SM (S), Target®(T)

Therefore, SCT stands for SMC + Casing + Target®.

Interestingly the combination PSS (PIIC, Spawning, SM) didn’t produce any mushrooms. On the other side, the combination NCT (NCS/SMC, Casing, Target®) produced with 144 % the highest biological efficiency.

Impact of non-composted substrate & spent mushroom compost on the biological efficiency of Agaricus bisporus

Figure 4: Impact of non-composted substrate & spent mushroom compost on the biological efficiency of Agaricus bisporus (1st. letter: substrate, 2nd letter: timing, 3rd letter: supplement)[17]

To understand the influence of the timing better, let’s take a look at figure 5. The best time to add the supplement is at the casing phase. Doing so will increase the B.E. by 25 %

Influence of the timing of the supplementation on the biological efficiency of Agaricus bisporus grown on different substrate

Figure 5: Influence of the timing of the supplementation on the biological efficiency of Agaricus bisporus grown on different substrate (SMC, NCS, PIIC).[18]

Besides the timing, we see a difference between the two supplements. The supplement Target® increases the B.E. by 25 % in comparison to the SM supplement (Fig. 6).

Influence of the supplement on the biological efficiency of Agaricus bisporus grown on different substrate

Figure 6: Influence of the supplement on the biological efficiency of Agaricus bisporus grown on different substrates (SMC, NCS, PIIC).[19]

The next study helps us understand the influence of various parameters of the casing layer on biological efficiency. The authors mixed spent mushroom substrate with coconut fiber pith in different ratios (Fig. 7). They also added calcium carbonate (100 g/L) to the mixture.

As figure 7 indicates, not all combinations could get close to the control batch, but some did. 

The second thing that stands out is that only one mixture with spent mushroom substrate reached a similar B.E. than the control.

Impact of different casing materials of SMS on the biological efficiency of Agaricus bisporus

Figure 7: Impact of different casing materials of SMS on the biological efficiency of Agaricus bisporus[20]

To understand these results, let’s take a closer look at figure 8. In this figure, we see the correlation of different parameters of the casing layer and the biological efficiency (B.E.).

This chart underlines what I wrote in the beginning. Spent mushroom substrate (SMS) contains a lot of salt, which will lead to a higher electrical conductivity (EC).

As the EC has a negative correlation with the B.E. adding to much SMS to the casing layer will reduce the B.E.

With that in mind, we now understand the results of figure 7 better. While the first mixtures with SMS (5:0 and 4:1) are still leading to a high B.E., the next mixture with a ratio of 3:1 resulted already in a lower B.E.

Correlation between different parameters and the biological efficiency of Agaricus bisporus

Figure 8: Correlation between different parameters and the biological efficiency of Agaricus bisporus[21]

Regulations concerning spent mushroom substrate

As I showed you in the last two chapters reusing of spent mushroom substrate (SMS) is possible.

When it comes to SMS itself, there are several things, especially regulations concerning this topic. In the next short paragraph, I will give you some head start. Still, please check your national and regional legislation to avoid any negative consequences as this article is only for educational purposes only and not legal advice. Especially because there are too many different regulations (Fig. 9) out there and I by no means a lawyer.

Summary of controls and regulations concerning spent mushroom compost

Figure 9: Summary of controls and regulations concerning spent mushroom compost (SMC) disposal in the United States, the Netherlands, the United Kingdom, Canada, and Ireland.

The author of this study[22] mentioned the following aspects:

SMC management policies

  • Except for the US, none of the studied countries [US, Canada, Netherlands, UK, and Ireland] has special or standard legislations that are specifically enforced for the correct management of SMC immediately after cropping.

Disinfection before disposal

  • Recommended disinfectants for disease control following cropping are [..] variable worldwide and, in some cases, are not applied and/or not legislated.

Storage of SMC

  • For mushroom growers who organize SMC removal as soon as it is produced, permanent storage facilities are not mandatory on the farm. However, for the majority of production units, temporary or permanent SMC storage facilities are required as the land-spreading of waste materials is generally prohibited for the winter months.

Utilization of SMC

  • Utilization confines exist for diverse end-uses of SMC. The factors that determine the further use of SMC in agriculture or horticulture include nutrient and salt content, substrate maturity, water-holding capacity and the presence of weed seeds, insects or pesticides (Anonymous, 2004a).

As I said earlier, please check if any regulations concerning these points or others are applying to you. To do so, you can, for example, use the next figure 10, which illustrates the handling of spent mushroom compost (or substrate) within one country as a guide. But it doesn’t replace talking to a lawyer.

Authorized situations for spent mushroom compost (SMC) under residual waste regulations

Figure 10: Authorized situations for spent mushroom compost (SMC) under residual waste regulations (adapted from Anonymous, 1997b) (MFEMP, mushroom farm environmental management plan)[23].

Now I want to hear from you:

What do you do right now with your spent mushroom substrate?

And did you get excited reusing your spent mushroom substrate while reading my article?

Let me know by leaving a quick comment.

Literature

Rinker 2017

https://www.researchgate.net/publication/319118864_Spent_Mushroom_Substrate_Uses_Technology_and_Applications?enrichId=rgreq-f889550500f2ab85fe6faf2f3f97af40-XXX&enrichSource=Y292ZXJQYWdlOzMxOTExODg2NDtBUzo1NDY0ODU5MTA0MjU2MDBAMTUwNzMwMzgwMjk3MA%3D%3D&el=1_x_2&_esc=publicationCoverPdf

NRCM FAQ

http://nrcmushroom.org/FAQ_on_SMS.pdf

Phan 2012

https://www.researchgate.net/publication/232229782_Potential_Uses_of_Spent_Mushroom_Substrate_and_Its_Associated_Lignocellulosic_Enzymes

Attri 2019

https://de.scribd.com/document/438699229/ProductionMarketing-BLA-pdf

Siobhán 2007

https://www.epa.ie/pubs/reports/research/waste/STRIVE_74_web.pdf

Ashrafi 2017

https://www.banglajol.info/index.php/JBAU/article/view/35069/23664

Pardo 2012

https://www.actahort.org/members/showpdf?booknrarnr=933_33

Royse 1992

https://link.springer.com/article/10.1007/BF00174464

Matute 2011

https://link.springer.com/article/10.1007/s11274-010-0582-5

Mamiro 2007

https://link.springer.com/article/10.1007/s11274-007-9364-0

Pardo-Giménez 2008

http://revistas.inia.es/index.php/sjar/article/view/361


[1] Rinker 2017

[2] https://www.fortunebusinessinsights.com/industry-reports/mushroom-market-100197

[3] NRCM FAQ

[4] Phan 2012

[5] Attri 2019

[6] Rinker 2017

[7] Phan 2012

[8] Siobhán 2007

[9] Ashrafi 2017

[10] NRCM FAQ

[11] Own figure based on Pardo 2012

[12] Royse 1992

[13] Own figure based on Royse 1992

[14] Matute 2011

[15] Own figure based on Matute 2011

[16] Mamiro 2007

[17] Own figure based on Mamiro 2007

[18] Own figure based on Mamiro 2007

[19] Own figure based on Mamiro 2007

[20] Own figure based on Pardo-Giménez 2008

[21] Own figure based on Pardo-Giménez 2008

[22] Siobhán 2007

[23] Siobhán 2007

7 thoughts on “Can you reuse spent mushroom substrate?

  1. I was very interested to read the results of using spent shiitake substrate for oyster production. I was wondering if you have tried or know of any studies using spent oyster substrate for further oyster production? Thank you for writing this wonderful article!

    1. Hi Mikie, thanks for your feedback. I know one study done by Ashrafi. The authors wrote exactly about the topic you are interested in. I did a video about this study. You can find the video either under the menu videos/substrate or on my YouTube channel.

  2. Franck Jacques Prissert says:

    sorry for the beginner’s question, but where do I get the spam now that I have the substrate?

  3. Hi there, this is very interesting.
    Would you know which supplements to the substrate will work if I use steam pasteurizing method to pasteurize straw or wood for 4 hours? Cold lime pasteurizing is also an option for us, but we are unable to use a pressure cooker.

    Also, is it possible after pasteurizing to grow the same type of mushroom on the newly formed substrate, or is it best to cycle? We grow king oyster, and grey oyster.

    Thank you for sharing your knowledge!

    1. Hi, Thanks. You could use, for example, wheat bran. If you are pasteurizing wood, then 4 hours won’t be enough. Here, 10 to 15 hours are found best, especially if you use supplements. Cold pasteurization would work for straw but not for wood. Do you want to use any of the mentioned pasteurization methods for spent mushroom substrate?

      Studies could show that you can grow grey oyster mushrooms on spent mushroom substrate.

      1. Yes, I was thinking of mixing my spent substrate 50:50 with fresh sawdust/woodshavings after pasteurizing. But if the wood would take that long to steam pasteurize, maybe sticking to straw with grey oysters would be better? Our steaming possibility is smaller quantity than our cold lime pasteurization quantity.

        If I use straw, could I steam pasteurize the spent substrate and cold pasteurize the fresh part, or what would be the best way to go about this? And are there good supplements that can be used with this method to increase BE for straw?
        Or maybe fermentation is an option?

        Unfortunately a pressure cooker is not an option where I live, so I’m trying to figure out the best way to go about this with the little money we have. Recycling old substrate would greatly reduce waste and increase the yield per dry substrate cost by a lot for us.

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