Growing with bulk substrates (2024)

Bulk substrates are mildly nutritious materials used in mass mushroom cultivation. Bulk substrates are often used in conjunction with a pre-colonized grain spawn substrate. That spawn is then used to inoculate the bulk substrate.

Common bulk substrates[]

• Manure (horse, cow, elephant, etc.)
• Coconut coir is the shredded fiber of coconut husks. It holds many times its weight in water but does not decompose for years. It is PH neutral and inexpensive. Hydroponics stores and hardware stores sell it in compressed bales & pet stores sell it in dried bricks.
• Straw
• Worm castings
• Compost

Creating Grain Spawn[]

Bulk substrates cannot be inoculated using liquid culture or spore solution, and so one of the first steps in a bulk grow is creating grain spawn in order to inoculate the bulk substrate.

Once your grain spawn is fully colonized it can be mixed with your pasteurized bulk substrate in a process called Spawning

Recipes for Bulk Substrate[]

While straight horse manure or straw are often used with great success, some cultivators choose to mix in different ingredients in their substrate to either create a texture and structure which will facilitate colonization, hold moisture, adjust pH, or add nutrition. Some ingredients cannot or should not be used by themselves. For example cow manure must have straw or coir added to it or else it will become like mud when wet and will not colonize properly. Worm castings are sometimes added in small amounts for nutrition, but make poor substrates by themselves because, like cow manure, they become like mud when wet, and because they are not as nutritionally balanced as cow or horse manure.

Here are a few simple recipes that can be used:

Recipe 1

• 1 part horse poo
• 1 part vermiculite (or coir)

Recipe 2

• 2 part horse poo
• 1 part vermiculite
• 1 part coco coir

Recipe 3

• 1 parts straw
• 1 parts cow poo

Here is a more complicated recipe:

High Potency Recipe

• 30 Cups Shredded Horse Manure
• 16 Cups Vermiculite
• 14 Cups Coco Coir
• 4 Cups Organic Worm Castings
• 4 Cups Garden Gypsum
• 2 Cups Spent Coffee Grinds
• 3 Tablespoons Kelp Meal
• 4 Tablespoons Vegetable Oil
• 1.5 Tablespoons Hydrated Lime (add before hydrating)
• A tad under 1.5 gallons Water (use best judgment after first gallon added)

(Note: This recipe was originally intended to be sterilized and fruited in spawn bags rather than pasteurized and included Wild Bird Seed. Since you will be using grain to spawn to this substrate, I figured I could remove it. To read the original tek click here)

Moisture Content of Substrates[]

Mushrooms are 90% water when fresh, and so having the proper amount of moisture in your substrate is of vital importance for Fruiting as well as colonization.

The level of proper hydration is called "Field Capacity". It is the optimum level of hydration in which the substrate is holding the maximum amount of water while not being too wet, and the minimum amount of water that is needed for proper colonization and fruiting.

To tell when your substrate is at field capacity mix in your water very thoroughly to be sure that the moisture is distributed evenly throughout. Pick up a handful of your substrate and give it a squeeze. If it is at field capacity water should drip out with a light squeeze, and a small stream of water will drip out with a hard squeeze, and no water should drip out at all if not squeezed.If it is below field capacity, water will not drip out when squeezed. If water is dripping out without any squeezing at all then you have over-saturated the substrate.

Pasteurizing Bulk Substrates[]

Bulk substrates are pasteurized rather than sterilized. Pasteurization allows certain beneficial bacteria to survive in the substrate, which prevents harmful bacteria or mold from growing.

To pasteurize a substrate it must be kept at a temperature of 160-180F for 1-3 hours. Going any higher than 180F will kill the beneficial bacteria and greatly increase your chances of contamination.

There are many different methods by which a substrate can be pasteurized such as:

• Filling a pillow case with substrate and soaking in hot water. Then removing the pillow case from the water and allowing it to drain and cool. Pillow Case Pasteurization Tek

• Filling a plastic "oven bag" with substrate and baking in an oven at 160-180F for 2-4 hours.

Spawning Grain to Bulk Substrate[]

Once your grain spawn is fully colonized it is ready to be spawned to the bulk substrate (note that the word "spawn" is used as a noun when referring to the colonized grain, and also a verb when referring to the act of mixing it with the bulk substrate).

• Step 1: Put your pasteurized substrate in a container in which it can be mixed up with the spawn. This may be the intended fruiting chamber, another large plastic tub, or even the bag in which the substrate was pasteurized.
• Step 2: Shake spawn jars so that the colonized grain is broken up and is no longer in large clumps.
• Step 3: Mix in the spawn with the substrate as evenly as possible. If the spawn is not evenly distributed within the substrate, colonization of the bulk substrate may be uneven, causing it to take longer thus allowing more time for contaminants to grow.
• Step 4: Place substrate in the fruiting chamber and put in a dark place so that it can colonize. Depending on how much spawn is used, colonization may take 5 days to 2 weeks. The more spawn used the faster the bulk substrate will colonize. Recommended spawn ratios are usually no less than 20% (1 part spawn to 4 parts substrate).

Notes:

• Some cultivators choose to cover the uncolonized substrate with a layer of plastic wrap or tin foil after spawning. This is done to keep moisture in the substrate, block out contaminants, and limit airflow so that higher CO2 levels simulate the conditions of the underground stage of the fungus' life cycle in nature. This is of course completely optional, and the advantage it may have can certainly be debated.
• Since your substrate has been pasteurized, it is much more resistant to contamination than a sterilized substrate would be (ex. grain jars, or PF Jars). Spawning can be done in open air in a room that would not be clean enough for inoculation. The fact that cleanliness does not have to be so strict is a major advantage of using pasteurized substrates. However, any measures you take to ensure that spawning is done in a clean environment can ONLY decrease your chances of contamination.

Fruiting Bulk Substrate[]

After the substrate is totally colonized it is ready to be put in fruiting conditions.This requires fruiting chambers suited for bulk growing such as a monotub or double tub. You can also use a tarp outside .