Grow mushrooms the EZ way.

Bulk Substrate for growing mushrooms.

Bulk Substrate Recipe


If you are planning to grow mushrooms, chances are you will need a bulk substrate. A bulk substrate is simply a mixture of ingredients that can be used to grow mushrooms.

There are many different recipes, but all of them have the same goal: to provide the mushrooms with nutrients and water to grow. In this blog post, we will discuss the basics of bulk substrate.

If you are looking for a recipe or guide post checkout how to prepare mushroom substrate.

What is a bulk substrate?

It is a medium that contains all of the necessary nutrients for mushroom growth. It is typically made up of organic materials, such as straw, sawdust, and manure. These ingredients can vary depending on the type of mushrooms you are trying to grow.

For example, oyster mushrooms can thrive on straw substrate whereas Lions mane mushroom would prefer a hardwood sawdust substrate.

Mushroom substrates can be seen in a similar fashion as soil is to a plant, the grain spawn is sown (known as inoculation) into the substrate where the mycelium expands at an exponential rate, eventually producing mushrooms.

Mushroom substrate isn't sterilized unless you are using supplementation in the mix, instead you should pasteurize it.

Regardless, it is probably a good idea to buy a pressure cooker anyway as you can use it for pasteruization too, checkout my post on pressure cookers here.

Why use a bulk substrate?

Substrates are used because they provide a very large surface area for mycelium to colonize.

This surface area is important because it allows the mushrooms to produce more fruit bodies (mushrooms), the larger the surface area the more nutrients and water the mycelium can use when producing mushrooms.

In addition, they are typically cheaper and easier to find than other types of substrates such as grains.

Most Common Bulk Substrates

In this section I will discuss the most common mushroom substrates I have used during mushroom grows these are:

  • Hardwood
  • Straw
  • Coco Coir
  • Manure
  • Hardwood


Hardwood substrate can come in many forms such as hardwood fuel pellets, sawdust or logs. I have used all three forms with great success but my favourite is hardwood fuel pellets.

This is because the pellets take up less space and make less mess than something like sawdust(before it is hydrated that is).

Hardwood fuel pellets are made from 100% hardwood with no fillers or binders.

They have been pressed into small pellets normally used for fueling fire or smoking food but are perfect for mushroom cultivation.

If you are buying sawdust spawn then the following are common types of hardwood you will be able to purchase easily:

  • Beech
  • Oak
  • Aspen

Common mushroom species grown on straw substrate are:

  • Oyster/King Oysters.
  • Shiitake.
  • Enoki.
  • Nameko.
  • Maitake.
  • Chicken of Wood.
  • Lions Mane.

Here are some photos of what the different hardwood bulk substrates I have look like.

Hardwood Fuel Pellets HWFP Bulk Substrate
Aspen bulk substrate
Hardwood oak bulk substrate


Straw is one of the more popular mushroom substrates for gourmet mushrooms.

It is often used to grow Oyster Mushroom as it has the perfect nutrient profile for encouraging growth without increasing the chance of contamination.

Alongside this, straws is cheap, easy to find and easy to work with.

Some common forms of straw used for a bulk substrate recipe while growing mushrooms are:

  • Wheat straw.
  • Oat straw.
  • Barley straw.

Common mushrooms species grown on straw substrate are:

  • Oyster / King Oyster.
  • Shiitake.
  • Nameko (although more likely to contaminate than on hardwood).
  • Enoki.
  • Wine caps.
  • Lions Mane.

Here is a picture of a few kilos of straw I bought. You can see you need significate room to store a bale like this, although you'' get plenty of grows out of this.

barley Straw Bulk Substrate

Coco Coir

Coco Coir is a substrate made from the husks of coconuts. 

It is a popular substrate for mushrooms because it is pasteurized before sale, easy to find, and holds a lot of water. 

Coco Coir is not very nutritious for the mushroom mycelium and so it is often used in conjunction with supplements like manure, coffee grounds or vermiculite. 

However some mushrooms will grow perfectly well from just coco coir.

Try to get Coco Coir which is not enriched with trichoderma however (coco coir for plants), instead get Coir which is prepared for reptile bedding. I usually buy this from hardware stores and pet shops.

If you can only get plant/garden Coco Coir don't worry I have used this before and it normally just means you have to be thorough with your pasteurization techniques.

The product comes in bricks which is cheap if you look in the right places. I found coir bricks in a pound shop once and bought 8-9 bricks at once and now have more than i know what to do with!

Once hydrated it puffs out to 10L of substrate, but the bricks are very compact and easy to store so be on the lookout.

If you are interested in using Coco coir as substrate checkout this recipe.

Common mushrooms grown on Coco Coir substrate are:

  • Oyster / King Oyster.
  • Lions Mane .
  • Reishi.
  • Turkey Tail.
  • Chestnut.

Here is a picture of the Coco Coir I found at the pound shop. You can see how easier this is to store than other substrates.

Coco coir substrate brick


This is a great substrate for mushrooms because it is high in nutrients (such as nitrogen) and water content.

It is important to note that you should only use manure from herbivores (animals that eat plants), as carnivore (animals that eat other animals) manure can contain harmful bacteria for humans when handling.

You won't have to spend money to get the material either.

Instead, you can buy it from local farms or even gather it yourself in cow fields or where horses are walked (although you might look a bit odd roaming around picking up animal faeces).

Normally it's a good idea to mix manure with coco coir as it is very nutritious and thick this helps to break it up a bit.

Common mushrooms grown on Manure substrate are:

  • Shaggy Mane.
  • Portobella.
  • Oysters/ King Oyster .

How long does it take for bulk substrate to colonize?

This will depend on a few different things like the age of your spawn, how you are storing it, what substrate you are using and the conditions you are growing in. 

However, in general you should start to see some mycelium growth within a week or two and completion within 4 weeks.

If I don't see a completely engulfed substrate which is all white within 4 weeks I will usually assume something has gone wrong. 

Often if I take a monotub or substrate out of its vessel and flip it or look around it I will find heavy contamination hiding somewhere.

What is the best bulk substrate?

For people just growing mushrooms at home as a hobby the best substrate is probably the one you can get lots of for cheap in your local area which the strain you are growing can cope with. 

This normally is one of the cereal straws mentioned in the straw section. 

Also take into consideration the amount of space you have storing 40L of coco coir is not the same as storing 5Kg of barley straw, checkout the photos in this post to understand why.

However, if we are talking about the actual best mushroom substrate i.e grow the largest flushes and provide the most nutrients then that would be masters mix.

Masters mix is commonly used by mushroom farms and consists of  equal parts of hardwood sawdust and soy hulls. Soy hulls provide a good source of nitrogen and essential trace minerals to the substrate, something mushrooms thrive on.

The main problem with masters mix are:

The cost, soy hulls like grains, cost quite a lot if used at scale.

High risk of contamination, because the mix is so nutritious you're going to need a laminar flow hood to work with it.

Personally I have never used Masters Mix as I have never felt the need to as I don't grow mushrooms to a commercial level. 

Where to buy them?

You can purchase substrate from loads of places such as: home & garden stores, pet stores, you can even pickup sawdust from furniture manufacturers who create it as waste (I think I got my oak sawdust from one of these on ebay cheap). 

Also check mushroom farms and stores online there are plenty of eCommerce stores selling mushroom growing items such as fuel pellets.

However, if you are feeling lazy here are a few amazon links for items discussed, I get a small commission for every sale:

Supplementing Mushroom Substrate

Once your substrate is fully colonized you might find that it doesn't fruiting as well as you want or the flushes are smaller than you'd like, this is normally where supplementation of the bulk substrate becomes relevant.

The following materials make good supplementation:

  • Coffee Grounds.
  • Manure.
  • Soy Hulls.
  • Vermiculite.
  • Gypsum.
  • Bran.

If you are going to add supplementation to your grows it could increase the chance of contamination so make sure you have non supplemented grows working before adding it.

Bulk Substrate Vs PF-Tek

The main difference between Bulk substrates and PF-Tek is that with substrates you are spawning your mycelium to a large amount of substrate at once, normally in a monotub. 

Whereas with PF-Tek you are spawning to smaller jars and then once colonized fruiting directly or transferring to a larger substrate (and using the PF-tek like grain spawn).

The main advantage of Bulk Substrates is that you can achieve much higher yields per tub/bag as you are providing the mycelium with a larger amount of substrate, nutrients and water.

The main advantage of PF-Tek is that it's much easier and less likely to contaminate as you're working with smaller volumes of substrate.

Wrap Up.

In my opinon main thing to consider is cost, species and space when buying a substrate.

I hope you enjoyed this post, hopefully you found what you are looking for.

If you have any questions feel free to leave a comment below.

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