Sawdust can be used as growing medium or as spawn for inoculating logs or outdoor mushroom patches. It is common practice to grow a variety of species on “blocks” made from enriched sawdust or a mix of sawdust and woodchip. By adding a nitrogen rich amendment to the hydrated sawdust before being sterilised the yield of fruit bodies can be increased significantly. A common additive used to enrich sawdust is wheat bran.


  • 1kg hardwood sawdust (1 – 5mm shavings)
  • 10 – 20g gypsum (calcium sulphate); 1 – 2% dry weight of substrate
  • 10 – 20g Limestone flour (calcium carbonate); 1 – 2% dry weight of substrate (optional)
  • 100g – 200g wheat bran ( 10 – 2 % of dry weight)


  • large mixing bowl or suitable container
  • jug
  • scales
  • filter patch mycobags
  • pressure cooker
  • kilner screw bands or other suitable “spacers”


  • sieve out finer dust
  • rinse sawdust with soapy water
  • soak for at least 24hrs
  • thoroughly drain
  • thoroughly mix sawdust with gypsum and Wheat Bran
  • optimise moisture content; avoid excess moisture
  • put into filter patch mycobags
  • ensure the bags are not touching the bottom or sides of the pressure cooker and there is space between the bags; use plastic spacers
  • sterilise at 15psi 2hrs



The first step in processing sawdust for use as a mushroom growing substrate is to filter out the finer dust particles. This prevents compaction within the substrate which could create anaerobic pockets. Simple sieve the sawdust but be sure to wear a face mask.

The most important factor for increasing yields is the moisture content of the substrate. However, excess moisture can create anaerobic environments and therefore encourage the proliferation of contaminants. Fresh sawdust is hydrophobic meaning that it resists water absorption so the longer you can soak the sawdust the better. I now soak sawdust in water for at least 24hrs after rinsing in soapy water to remove any unwanted grease and finer particles.

Drain the sawdust so it is not dripping wet. You are now ready to add the the gypsum (limestone flour is optional but don’t skip out on the gypsum) and wheat bran. The gypsum adds calcium  and sulphur for fungal development. It will not alter the PH of the substrate, this is the role of Limestone flour (calcium carbonate). Mix thoroughly and then fill the autoclavable mycobags to about two thirds. Try to ensure that the top of the bag is free from the mixture. If it does get round the inside top of the bag wipe it off with a paper towel. Now fold the top of bags down so there’s no excess air in the bag, ensure that the bags don’t unfold during the sterilisation, you may have to use some tape to secure them. Now place into the pressure cooker making sure the bags aren’t touching the bottom of the sides of the pressure cooker. Bring it up to 15psi and cook for 2hrs. Leave to cool for 6 to 8 hours before opening in a sterile environment for inoculation. Do not move the pressure cooker until it has returned to 0psi.



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