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The Best DIY Monotub Substrate Recipe!

The Best Monotub Substrate
Updated on 09/01/22

Are you looking for the best monotub substrate to turn your gourmet mushroom spawn into a vast and never-ending forest of caps and stems—all without using stinky manure?

If so, stray no further!

This is the absolute best and easiest bulk substrate recipe that is guaranteed to take your monotub yield to the next level!

Let’s waste no more time and get into it!

What is Monotub Substrate?

Coco Coir - Bulk SubstrateSo before we jump into our monotub substrate recipe, let’s first briefly cover what monotub substrate is and why we as mushroom growers use it!

To start, monotub substrate—more commonly referred to as “bulk substrate”—is nothing more than a nutritious growing medium that we can use to significantly increase the yield from our mushroom spawn.

By simply mixing our mushroom spawn with a bulk substrate in specific quantities, we can more than double—sometimes quadruple—the colonized growing surface for our mushrooms.

Pretty cool huh?

So let’s get into the substrate recipe and start bulking up your mushroom yield!

The Best DIY Monotub Substrate Recipe!

Alright, let’s waste no more time. The best monotub substrate is Coco Coir mixed with vermiculite and gypsum.

But why these ingredients and in what proportions? Let’s jump into the directions and then briefly discuss each ingredient’s purpose and necessity so you can custom your DIY substrate to your needs and climate.

Supplies Needed:

Why Use These Ingredients?

So before we jump into the directions on how to prepare your bulk substrate, let’s quickly cover the characteristics of each ingredient and why they help make the best medium for growing mushrooms!

Why Coco Coir?

Coco Coir Brick - Mushroom SubstrateCoco Coir is a relatively cheap material made from the husk of coconut shells. It makes the perfect mushroom growing medium as it retains water very well and is highly resistant to contaminants such as bacteria and mold.

Because of this natural resistance to contaminants, it is a very forgiving material, which makes it great for those just beginning their mushroom cultivation journey or for those who just want a low-maintenance substrate!

This material works so well that you could skip the other ingredients on this list and make a 100% Coco Coir substrate. However, I would still recommend using the other ingredients as you’ll soon learn why.

I highly recommend Plantonix Coco Coir Bricks. They are 100% organic and come in packs of 5 bricks that store easily for when you need them!

Why Vermiculite?

Vermiculite - Bulk Mushroom SubstrateMushrooms require a lot of water during the fruiting stage, and vermiculite is a non-nutritious material that is really good at retaining moisture.

Now the necessity of vermiculite truly depends on your climate.

If you live in an area with higher humidity—such as on the coast—you’ll be okay skimping out on this ingredient, but I still recommend always using it.

However, if you live in the desert or anywhere with a drier climate, for the sake of your sanity, please include vermiculite!

Remember, dry substrate = sad mushrooms.

Why Gypsum?

Gypsum—also known as calcium sulfate—is a common material found in drywall. As a matter of fact, if you have some old drywall laying around, you can crumble it up and use it in place of gypsum if you wish.

Gypsum not only adds minerals for your mycelium to feast on but also acts as a PH stabilizer by adding calcium carbonate (alkaline) and sulfur (acidic) to your substrate!

This is a very optional ingredient as you will easily find success without it.

However, if you can, it only helps to throw it in!

Monotube Substrate Directions

With the ingredients out of the way, let’s finally throw it all together and make our bulk substrate in three easy steps!

Step One: Prepare The Water!

Okay, so our first step is to boil some water for pasteurizing our substrate. Pour 4 quarts of filtered water into a pot and turn the heat on high until it comes to a rolling boil. While you wait, you can move on to the next step!

Step Two: Mix Everything Together!

While you’re waiting for your water to boil, add your 8 quarts (or 1 brick) of Coco Coir, 2 quarts or vermiculite, and half a quart of gypsum into your 5-gallon bucket. Once your water has come to a nice rolling boil, pour it into the bucket as well.

Step Three: Close It Up and Wait!

With all of your materials in the bucket, throw the lid on, and let it sit for an hour. After which, open it up, give it a good stirring, and close it back up again. Let it sit and pasteurize for at least 6 hours and perhaps a little longer to cool before adding it to your monotub!

That’s all there is to it!

Note: Before adding your spawn, you absolutely need to make sure that your bulk substrate has sufficiently cooled. Anything above 90°F degrees could be hot enough to kill your mycelium. Remember, growing mushrooms is a game of patience—at every step.

What is the Best Spawn to Monotub Substrate Ratio?

Alright, so you’ve got your monotub substrate all mixed and ready to go, but how much substrate do we mix with our mushroom spawn?

Sadly, this isn’t a simple answer and completely depends on your own risk to reward tolerance.

You see, the more bulk substrate you use to mushroom spawn, the slower your monotub will colonize and the greater chance you have of your tub becoming contaminated. However, the upside of using more bulk substrate is you will have more total substrate to spawn mushroom—which means more mushrooms!

On the flip-side, using more spawn per bulk substrate will decrease the chances of contamination; however, your mushroom yield will also be smaller.

I recommend one of these three ratios:

1:1 Spawn to Bulk Substrate

This is going to give you the lowest mushroom yield; however, it will also give you the lowest probability of contamination.

1:2 Spawn to Bulk Substrate

This ratio will give you a 50% greater mushroom yield; however, you will also increase your chances of contamination.

1:3 Spawn to Bulk Substrate

This ratio will give you a 100% greater mushroom yield; however, it will also give you the greatest chance of contamination of these three choices.

Note: I have successfully grown mushrooms using this tek with ratios as insane as 1:5. However, I wouldn’t recommend it unless you have a clean and somewhat sterile environment, such as a mushroom grow tent.

There you have it! The best bulk mushroom substrate for your monotub! Making your own DIY substrate doesn’t have to be complicated nor expensive, and you seriously can not go wrong with any of these ingredients.

I hope you enjoyed this little guide and consider checking out our other mushroom cultivation guides.

Also, be sure to leave us a comment below and let us know how this recipe worked out for you!

Have a fruitful harvest!