Bulk Substrate

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Bulk Substrate

Bulk substrate allows you to grow a respectable amount of mushrooms and requires some space and experience. This is NOT recommended for first timers. Bulk substrates usually contain a combination of equine (horse) dung , straw, organic compost, coir, worm casings, wood chips, or sawdust.

Summary of the Process

Bulk Substrate should be pasteurized (pasteurization) and allowed to cool. Once cooled it is then spawned with colonized grain, mixed, and allowed to colonize in tubs or trays. Colonized bulk substrate is be introduced into fruiting conditions where mushroom growth is expected to occur.


Coir and manure based substrates seem to be the trend among home cultivators. Following are the three most recommended recipes for at home cultivation of grain and/or dung loving mushrooms.

Coir Recipe
Coir, limestone, wormcastings, and vermiculite in a large container ready to be pastuerized.

1 Brick Cocoir (expands to 8 quarts) 2 Quarts Vermiculite ½ Pint of pH buffering material such as crushed limestone ½-1 Pint odorless worm castings (optional)

Manure Recipe
A Pastuerized horse poop ready for spawn material.

8 quarts field aged shredded dry horse poop 8 quarts finely shredded wheat straw

Advanced Recipe- Super Duper Pooper Mix Substrate 2 Quarts field aged shredded dry horse poop 1 Brick Cocoir 1 Pint odorless worm castings 2 Quarts Vermiculite 1 Pint crushed limestone 2-10 Quarts finely shredded wheat straw

(You may increase or decrease any amount of poop, coir, or straw to this recipe)



Pasteurization uses heat at a specified temperature to kill off “bad” micro life, and allow “good” or beneficial micro life to survive.

For cubensis species the specified pasteurization temperature is 170 F for at least one hour.

For agaricus and other edible species the specified pasteurization temperature varies. Agaricus for instance, require more microlife in general to fruit, therefore bulk substrates for this species are typically pasteurized at 150F for one hour.


Directions for Pasteurizing Any Substrate

Materials Needed

Large cooler or rubbermaid type tub with lid

Large pot(s) for heating water

Meat thermometer

Large wire strainer

Gloves (rubber or dish gloves)

Large stirring utensil

Additional container to put finished product in storage

Note: Different mushroom species require different pasteurization temperatures.

  Cubensis generally require 170F for at least one hour

1. Place bulk ingredients in a LARGE tub or cooler.

2. Heat Several Large Pots of water on the stove to 175F

3. Add a couple gallons of hot water to the substrate to thoroughly hydrate it, then mix well. Coir will take several minutes to fully expand.

4. Add water from the stove that was preheated to 175F. Add enough water so that the substrate is floating in the water.

5. Check the temperature of the substrate/water bath. Add hot water as needed until the temperature is exactly 170F.

6. Close the lid and wait one hour.

7. Recheck the temperature. If the temperature is above 160F after one hour, close the lid and allow the mixture to cool enough to be handled. This usually takes 2-4 hours.

   If the temperature is below 160F, add more hot water to bring the temp back to 170F, close the lid and start the time again.

8. Put your gloves on. Dip the substrate out of the water bath and allow the excess water to drain back into the tub. Then squeeze each handful until it is to field capacity. Generally it is squeezed until barely a drop of water can be squeezed out by hand pressure.

9. Put in a clean rubbermaid and allow to cool before spawning.

Note: Substrate can be prepared up to a week ahead of time, and kept in a sterilize or rubbermaid with a filter patch. Pasteurized manure substrates can be frozen and thawed a couple days prior to use without repasteurization.

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