How to Make a Monotub: The Complete Monotub Tek Guide

Step 1: Make or buy mushroom grain spawn

First off, you'll need to get your mushroom grain spawn colonizing so it can be used in your monotub. Grain spawn is sterilized grain that has been fully colonized with mushroom mycelium. (It's the equivalent of seeds for mushroom growers).

There are a number of different options for procuring mushroom grain spawn. If you are growing any common edible species of mushroom you can buy fully-colonized grain spawn. Just keep in mind that the substrate you'll put into your monotub will change depending on the species you choose.

If you plan to grow a dung-loving mushroom species that isn't commonly available, you will need to make your own.* To do that, you will need a sterilized grain bag with injection port.

Sterile grain bags (also called spawn bags, mushroom grow bags, or grain substrate) are filled with a blend of sterilized grains. (Ours features a blend of hydrated millet and wheat berries.) The bags feature a self-healing injection port meant to work in tandem with a spore or culture syringe. If you're looking for common edible mushroom species, North Spore offers gourmet liquid culture syringes. If you are looking for medicinal spore syringes, these can be purchased online from sites like Sporeworks.*

Be aware that although hallucinogenic mushroom spores are legal in most jurisdictions in the United States for microscopy use (studying them under a microscope) the millisecond they form hyphae and become mushroom spawn or mycelium or are used with intent to cultivate mushrooms they become illegal. Hallucinogenic mushroom spores themselves are illegal in a number of U.S states including the state of California. Be aware of the legality in your place or residence!

If you're looking for ready-made spawn, North Spore carries a wide variety of USDA certified organic colonized grain spawn.

You'll notice the white mycelium growing outward from the injection point. When it has grown three to four inches you should, without opening the bag, carefully break up the colonized grain and mix it into the uncolonized grain. This will dramatically speed up the colonization process.

When the bag is completely white with mycelium your spawn is ready to use. This may take a couple weeks to a month or more depending on the species and vigor of your culture.

We recommend our Boomr Bag product for any manure loving species. It's easy to use, already cooked and sterilized, and is a formulation perfected over many years of Agaricus trials. It will save you the hassle of tracking down your own ingredients and cooking horse poo at home...

If you decide to make your own manure substrate blend the easiest formulation is 50% coco coir and 50% horse manure. Coco coir can be purchased by the bag from most grow shops specializing in hydroponic or urban gardening. The best horse manure will have to be sourced from farms that board horses, offer riding lessons, etc. Best is manure that has been composted for at least 6 months.

At this point you can either pasteurize your bulk substrate by cooking it in an oven or steaming it. You'll need to mix the two ingredients together and hydrate the mixture to 'field capacity.' If you grab a handful of the substrate and squeeze it as hard as you can you should be able to get one or two drops of water to drip out. More than that and the mixture is over-hydrated: add more coco coir. If it is under hydrated add water little by little and continue to test it.

For the oven method just preheat it to 170 degrees and cook the bulk substrate on baking pans with a tinfoil cover for at least 2.5 hours.

To use the steam method, bag the substrate in filter patch bags and cook it in a pressure cooker or steam it until it reaches around 160-180 degrees F.

Allow your bulk substrate to cool completely before using it!

There are many ways and materials you can use to make a monotub. Most frequently large Tupperware style containers are used such as those made by Sterilite. If you choose to use this type of clear plastic container, we recommend using an opaque plastic bag as a liner for the bottom of your monotub to help prevent mushrooms from growing on the sides or bottom. The mushrooms that grow this way are nearly impossible to harvest yet will use up valuable nutrients and energy from from your substrate. Best to keep them from growing in the first place and allow the mycelium to put all its energy into creating mushrooms in easily harvestable parts of the tub.

Since first making this article and its corresponding video walk-through, we've learned that it is better to use a liner than to spray-paint the outside of your monotub. As your bulk substrate colonizes with mushroom mycelium, it will pull away from the sides of your monotub but still cling to your liner. This prevents the monotub from forming microclimates suitable to side pinning. Consensus is that light proofing the lower half of your monotub is not necessary, though we've found that it does marginally help prevent side pins.

Now for the fun part! The amount of bulk substrate and spawn you use will be dependent on the size of your monotub. You want to have 3-5 inches of substrate. One 3lb injection port bag should readily inoculate one or two moderate sized tubs.

You want to start by sprinkling about one inch of bulk substrate into your sterilized monotub, or in the liner if you're using one. Make sure your bulk substrate is still at field capacity (see if you can squeeze out a couple drops of water from it!) If it dried out during pasteurization you'll need to add sterilized water to the blend as your fill your tub.

Then add a thin sprinkling of colonized grain spawn. Add another inch of substrate followed by more spawn. Keep sandwiching spawn in layers of bulk substrate until you've reached your desired depth.

Step 6: Watch the monotub for signs that it's fully colonized

Check on your bin daily to watch it colonize. You'll see white spots start to expand from each point of grain spawn. Over time they will completely cover the surface of the bulk substrate. You should see small droplets of mushroom exudate. This is natural and a sign of proper hydration and a speedy colonization.

You want to look for the signs of pinning mushrooms. This usually looks like white hyphae growing pinning vertically from the surface of the substrate and forming little knots of dense white mycelium.

Tubs will take 2-3 weeks to fully colonize for most dung loving species. Wood loving species colonization rates will vary.

When you start to see hyphae knots or pins you'll want to case your monotub. You can now safely remove the lid from your bin.

Add a thin 1/2 to 1 inch casing of 100% coco coir to the bin and spray the bin with water until the casing is showing signs of being fully hydrated. Some growers recommend using vermiculite to case monotubs but new research into the connection between vermiculite mining and contamination from asbestos should give pause to this practice. Coco coir works equally as well and is a safe alternative.

Spray the tub daily with water and keep the lid of the bin slightly offset to allow a bit more oxygen flow to the tub. Make sure the bin gets some light to allow the mushrooms to grow in the correct direction. Although mushrooms don't photosynthesize like plants do, light still helps them grow healthy and in the correct direction!

Harvest your mushrooms at the stage you desire. For most species this is before the caps have flattened out.