How to Make a Monotub: The Complete Monotub Tek Guide for Growing Mushrooms

There are many ways and materials you can use to make a monotub. Most frequently large Tupperware style containers are used. Though we used two sizes of holes for our build, there is flexibility with hole placement and size depending on which species you're going to be growing in your tub. We designed our tub with flexibility and airflow optimization in mind for growing the widest range of mushroom species. But for growing one certain variety of medicinal mushroom you can get away with just the two inch holes.

You will be drilling a total of six 2 inch holes around the perimeter of your tub: two holes on each long side and one hole on each end about 8 and a half inches from the base of the tub. Then, you will drill 1 inch holes positioned approximately 4 and a half inches from the base. Ideally, the smaller holes should be just above the top of your substrate. The bin we used is roughly 20 inches wide, so our 1 inch holes are positioned at 5 inches, 10 inches, and 15 inches across.

Start by measuring out and marking where your holes will be. Then, use the drill and small bit to drill pilot holes in the centers to avoid cracking.

Using your 1 inch and 2 inch hole saw bits, create the holes, being sure to drill in reverse. Drilling forward rips at the plastic and can cause cracking, while reverse is easier and melts the plastic (drilling in a well-ventilated area and wearing a mask are not bad ideas!).

Finally, clean up the rough plastic edges of the holes using your knife.

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 Eden Shrooms.*

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.

As a reminder, liquid culture is composed of live mycelium suspended in a sterile nutrient broth, and culture syringes offer a clean and convenient way to introduce your favorite edible and medicinal mushroom mycelium directly onto grain, supplemented bulk substrate or all-in-one bags like our ShroomTek. Spore syringes, while convenient for some projects, offer a genetic grab bag of strains with the potential for unwanted traits and qualities. Compared to spore syringes, liquid culture exhibits more rapid colonization once introduced as the mycelial fragments do not require germination.

To inoculate your 3lb injection port grain bag, simply inject 2.5 - 5cc of spore syringe or liquid culture through the port in a sterile (or at the very least impeccably clean) location like our NocBox. Make sure to sterilize your hands, the syringe needle, injection port bag, and inoculation surface with rubbing alcohol. And always wear nitrile or latex gloves. Additionally, make sure to inspect the bag for any micro tears or contamination. Any tear in the bag will compromise its sterility.

If you've ordered a sterilized grain bag online, it is best practice to wait at least one week before injecting it to make sure that it wasn't damaged in transit. If it shows any signs of contamination (usually green mold) discard the bag. (If it's from North Spore, just reach out to us for a replacement!) Allow your bag to colonize in a cool location out of direct sunlight. The temperature for incubation shouldn't exceed 75 degrees F or dip below 55 degrees. After a couple weeks or so, you should start to see mycelium growing on the grain. 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.

Inoculating a grain bag in a NocBox.

Liquid culture is a method of propagating mycelium within a nutrient-rich liquid medium and our Liquid Culture Kit gives growers the power to turn a spore syringe into liquid culture or to expand a single culture syringe into 30 times more liquid culture. Liquid culture can be used to inoculate sterile substrates like sterile grain bags, grain jars, and all-in-one grow bags, saving you time and money producing as many mushroom flushes as you desire from a single culture or spore syringe. Spore germination and mycelium cloning is swift, within just 7-14 days, and liquid culture can be refrigerated for up to 4 months. Liquid culture can be a far easier tool for making spawn than myceliated agar plates or master grain spawn as its use doesn’t necessarily require a laboratory or clean space, just a simple NocBox will suffice.

We recommend our Boomr Bag substrate 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.

This is a very very important step! You want to make sure you give your mushroom culture every advantage possible. Put some rubbing alcohol into a spray bottle and sterilize your entire tub. Spray your hands, your working surface, any scissors you might use to cut your spawn bag open etc.

Spray the outside of your spawn bag and your bulk substrate bags and rub the alcohol around the entire bag.

Make sure the room that you are inoculating in is clean! If you have pets make sure the room has been recently vacuumed (although not so recently vacuumed that there may be air turbulence or particulate matter floating around). Better yet, if you have access to a still air box such as our NocBox for mycology work, this would be a great time to use it!

Close windows. Close doors. Be paranoid about contamination.

A note on side-pinning - this is when the substrate cake shrinks into the bin over time, creating a microclimate between your cake and the side of the bin where mushrooms want to grow. As your mushrooms mature, they will be difficult to harvest, become particularly dirty with substrate or casing, or stop growing altogether due to low oxygen levels. One way to avoid this situation is to use a liner. This goes at the base of your tub and contains all of your substrate. We used 3.5 mil plastic sheeting. Liners are completely optional, but the addition of one may ease cleanup, ease harvesting, and increase total yield.

To make your liner, cut a square of plastic sheeting and measure it 3 to 4 in away from the base of the tub. Cover the bottom of the tub with even overhang on each side. Fold each corner and secure it with duct tape.

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. Again, this is a great time to make use of your still air box.

You want to start by adding a thin sprinkling of grain spawn into your sterilized monotub, or in the liner if you're using one.

Then add about an inch of sterile substrate followed by more spawn. Keep sandwiching spawn in layers of bulk substrate until you've reached your desired depth. 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 you fill your tub.

Boomr Bins showing the stages of cultivation (inoculation, colonization, and fruiting).

Next, add a humidifier to maintain the necessary ambient humidity levels, ideally between 80-90%, which are crucial for mushroom growth. Attach the humidifier hose to the side of the monotub by removing a filter patch and position the humidifier below the tub to manage excess moisture. A humidity controller with a sensor should be used to automate the humidity levels inside the tub. This controller will monitor the ambient humidity and activate the humidifier as needed to maintain the ideal conditions for mushroom fruiting.

Finally, if you are growing mushrooms in a dark space, incorporate full-spectrum or adjustable LED lighting to ensure proper mushroom development. Light is important for vegetative growth, primordial formation, and the production of compounds like vitamin D. These modifications will give you better environmental control, enabling successful cultivation of various mushroom species. By carefully managing temperature, humidity, fresh air, and light, you can expand the types of mushrooms you can grow in a monotub and achieve better overall results.