We recommend the default substrate as it comes out to be 25% Coco Coir, 25% Horse Manure, 25% Shredded Straw, 25% Vermiculite, plus the non-volume adding 5% Gypsum.

The default substrate is an ideal mixture that has been properly hydrated by bringing to field capacity, mixing, and then pasteurized. Comes in one filter patch bag. The coco coir is ideal for creating a fluffy substrate that has a better micro environment than horse manure alone.. The horse manure and straw increases the ash (minerals) and nitrogen content ensuring a higher biological efficiency than just coir. Vermiculite increases the water carrying capacity of the substrate along with making it more fluffy aiding to the micro-climate in the substrate.

Made the day you order and shipped as soon as possible.

About the substrate:

All variations of substrate has, by volume, 5% Gypsum (calcium sulfate) added.
All material is individually hydrated to field capacity before being mixed with the other substrate. It is done in this order to ensure that the substrate has the highest stable water content, which is important because it has been shown that available water during colonization and fruiting is one of the biggest factors when it comes to yield.

The individually hydrated substrates are ran through a trommel if appropriate and then mixed in the desired ratio using a cement mixture to ensure all substrate material is evenly distributed and that it is lose and fluffy, creating the ideal micro-climate for rapid colonization once the grain spawn has been added.

About the Coco Coir:
Coco coir is soaked in water for 24 hours. This long soak helps to ensure that it is properly hydrated. If it is not soaked for a long period, it can continue to absorb the water and become less than field capacity during shipping.

After the soaking it is ran through the trommel to ensure that it mixes properly with the other substrates and to remove any chunks of unwanted materials.

About the Shredded Straw:

The shredded straw is made from the smaller golden wheat straw and is processed to be approximately 1/2 inch in length. It is then brought to field capacity by soaking for at least 24 hours.

About the Horse Manure:
The horse manure is collected in a way to ensure that it is free of unwanted debris. It is aged outside in the sun with frequent watering to reduce ammonia and urea, and yield desirable nitrogen sources by growth of firefang (actinomycetes).

It is then ran through a 1/2 inch trommel to break it apart to ensure it mixes evenly with the other substrates.

Before it is mixed with the other substrate It is brought to field capacity by a long soak.

About the Vermiculite:

The vermiculite is Grade #2 from Therm-o-Rock. The size that is most suited for holding moisture and keeping the substrate loose and fluffy. It is brought to field capacity before being mixed with the other substrates.

Recommended Spawn Ratio:
3 lbs of grain spawn or 5 lbs of bulk substrate. You can buy sterilized grain in a filter patch bag with an injection port HERE

The 3lbs/5lbs ratio ensures a very rapid colonization rate and further increases the mineral and nitrogen content. By volume, this is about a 1:2 ratio. Any more spawn and the substrate structure starts to become less than ideal, and any less will of course result in slower colonization rates. you can use a 1/4 ratio without any risk of contamination, but colonization time and yield will be lower.

Note: If desired and requested by email first, we can also add Sphagnum peat moss to your substrate.

Buy Sterilized Grain HERE

Buy Casing Material HERE

Buy Complete Monotub Kit HERE

Buy Monotub Replacement Kit HERE
The monotub replacement kit comes with a 7 lbs bag of bulk substrate, & 3 lbs of sterilized grain.


Shipping time maybe up to 1 week. Do not order unless you are able to wait. This operation isn't Amazon Prime. Its a small business during a pandemic. We do not keep inventory to ensure product freshness. We make the grain to order.


SEE UPDATE July 8th 2020

Product Description

This sterilized hydrated grain is the perfect item for growing a bulk amount of mushrooms. We have taken all of the struggle, cost and work out of preparing the perfect grain substrate yourself and left the fun part for you.

Quickly getting perfectly made grain for spawn production for the new grower or the experienced but busy mycologist has never been easier or cheaper.

This milo grain is hydrated, sterilized, and is ready for inoculation. It comes in a sealed spawn bag with an injection port to make inoculation by liquid culture or spore suspension as quick and easy as it ever will be!

Important note about replacements

Occasionally the rigid corners of the bags get damaged during transportation. This can lead to contamination.
So if the bag contaminates before inoculation, we will replace it free of charge. Just send us a picture of the bag. Include the injection port in the image.

If the bag contaminates after you inoculate it, and you believe that it wasn't your fault, send us a picture and we will replace it for our cost. This will be $1.75 for the replacement bag, plus the shipping. To save on shipping we recommend buying more or having it replaced when you buy more as shipping one single bag costs $6.30, while shipping 8 bags only costs $2.07 per bag.


Simply inject some of spore syringe or liquid culture of your choosing through the provided injection port and wait for it to grow! We often see full colonization in one week.

Why Milo?

Milo is ideal for making mushroom spawn— We believe it is even better than rye for several reasons. Milo yields more inoculating points than other grain due to Milo's harder shell, and higher amylose starch, it is less sticky and breaks apart more easily allowing you to mix it thoroughly into your bulk substrate. Rye and other related grain has a starch in it that is stickier, which in addition to the rye seeds softer coating results in more difficulty breaking it up properly for ideal spawning.
Our Milo grain promotes rapid colonization, leaving contaminants with less opportunity to gain a foothold in your substrate.

We use it ourselves!

We use this product to make many of our oyster grow kits. We mix the colonized milo into shredded, hydrated and pasteurized straw, using just one pound of spawn for every fifty pounds of prepared straw. That means that your three pound bag can inoculate, at a two percent spawn ratio, one hundred and fifty pounds of prepared substrate, which can yield fifty pounds of oyster mushrooms! Many other mushrooms have a similar spawn ratio, though not all.

Technical specifications

The technical info below are approximations good enough for most mushroom grow operations.

Filter patch: 0.2 micron
Bag size: 5x4x19
Seal: Bag is sealed twice with a double sided heat sealer that is 10mm wide, yielding a total of 20mm (~0.8 inches) wide seal strip.
Moisture content: ~55%
Approximate protein content: ~5%
Grain: Red Milo Seeds (Sorghum bicolor, 615 grams)
Water: Municipal, 748mls
Additives: Gypsum, small quantities of pulverized coco coir, peat moss, sawdust, and straw.
LC/Spore Tolerance: Each bag can receive as much as 12ml of liquid culture or spore suspension without any issues. This assumes you allow the bag to expand and that it is shaken after inoculation. We recommend 0.5 to 3ml of liquid inoculate, but if time is an issue, more can speed up colonization rates.
Sterilization Method: 15 PSI for a minimum of 90 minutes.
Number of seeds (inoculation points) per bag: Average is approximately 17,000 seeds, but range is 15,990 to 18,750 seeds depending on grain size and weight added to bag

Volume including air gaps: ~1800ml - This volume is approximately 2.5 quart jars that are filled 75% full of grain.
Actual volume: 1300ml
The actual volume is useful for figuring out the volume when adding to substrate that is made of small particles such as coco coir, coffee grounds, or sawdust as the particles fill the gaps between the grain. In this case, adding 1800ml of the shaken grain to a fine particle substrate is likely to only increase the volume by 1250ml to 1350ml. If your bulk substrate is large and has gaps greater than the grain, such as is often the case with straw, the addition of grain may not cause a volume increase.

Inoculation & Colonization Service

You can also purchase fully colonized spawn bags with the species available, but this will result in at least a 2 week delay as we make it after it is ordered to ensure the quality of the product. If you are purchasing additional items from us in the same order, they will also be delayed by 2 weeks. You may find it is better to purchase the grain spawn in a separate order.

The grain in our grain spawn is as described above. It is then inoculated with liquid culture using a sterile needle in a clean room, under a biological grade laminar flowhood. Before sending it off, we examine it to ensure there is no bacteria or other fungi present.

We work hard on making it as easy as possible for you to grow mushrooms, so we also offer a service to inoculate and colonize the grain for you. After approximately two weeks, you'll receive fully colonized, ready to use spawn.

Custom Designed Grain

We realize that not all grain is perfect for all situations; you might want it to have a higher or lower moisture content depending on what you are doing - Just let us know, and we'll be happy to adjust the moisture content for your order. This service is free, but it may cause a delay.
In our experience

Ordering 2 Bags vs 3 Bags
The problem with ordering 2 bags is that mailmen will often forcefully shove the smaller 2 bags into the mailbox and we've had reports of this damaging our bags. They come in a padded envelope. If we use a larger box to alleviate this problem, it makes the shipping cost the same as shipping 3 bags, but then requires additional padding & labor of packaging the item. We prefer to send 3 bags instead, as this is a better deal for the customer, creates less waste, and is easier for us.