Introduction

The monotub is a very popular mushroom cultivation method, especially among beginner indoor growers. It is simple to make, fast, and requires neither sophisticated ventilation systems nor complex humidifiers. The principle is based on a perforated plastic bin equipped with filters to ensure air exchange while maintaining optimal ambient humidity. These conditions favor colonization, pinning, and mushroom fruiting.

Mushroom cultivation in monotub

Why grow in a monotub?

Growing in a monotub allows creating an ideal microclimate for mushroom fruiting, with good humidity levels and sufficient ventilation. It is a simple, economical, and effective method, widely used to produce mushrooms in quantity, especially Psilocybe cubensis. A single perforated plastic bin equipped with filters is enough to start cultivation on several kilos of substrate. The system requires little maintenance and offers good yields. Its main drawback: in case of contamination, the entire bin can be lost.

Disclaimer : Although this technique is often associated with the cultivation of psilocybin mushrooms (such as Psilocybe cubensis), it is important to note that growing these is illegal in many countries. This article does not promote it. We rather recommend cultivating edible mushrooms like oyster mushrooms, namekos, and piopinos. These wood-loving species are ideal for experimenting with this method, simply by adjusting the substrate according to the types of mushrooms you want to grow. This article is for informational purposes and aims to show how these mushrooms can be cultivated with simple and accessible techniques.

Necessary Equipment

Here is the necessary equipment to build and use a monotub:

• Transparent plastic container. A 60-liter container roughly corresponds to dimensions of 60 x 40 x 35 cm. This provides enough space for a substrate 8 to 12 cm thick and good aeration.
• Drill with bits to drill 2.5 cm and 5 cm holes.
• Microporous tape or filters to cover holes and limit contamination.
• Sterile substrate, suitable for the type of mushrooms you want to grow (wood-loving substrates or CVG substrate).
• Colonized or sterile grains (grains available here).
• Spray bottle to maintain humidity.
• Plastic sheet to create a liner at the bottom of the container.
• Isopropyl alcohol to sterilize equipment and work surfaces.
• Nitrile gloves for handling sterile materials.

Substrate Choice

The choice of substrate directly depends on the type of mushrooms you want to grow:

• Wood-loving mushrooms: like namekos or piopinos. Use a substrate based on wood chips/sawdust such as our optimal substrate. For oyster mushrooms, organic straw pellets can work well.
• Tropical mushrooms with coprophilic affinity : like psilocybes and coprins. Use a CVG substrate (Compost-Vermiculite-Brown rice cake) or an enriched mix based on manure, coconut, and vermiculite.
• Coprohilic mushrooms: such as Agaricus. Use a substrate based on composted manure.

Mushroom cultivation in monotub

At Mycosphere, we offer organic sterile substrates suitable for wood-loving mushrooms as well as sterile grains for inoculation.

Monotub Assembly

To build an effective monotub, here are the key steps:

1. Drill the holes: Most monotubs use Tupperware-type containers. You can customize the size and location of the holes depending on the mushroom species you are growing. Generally:
   • Large holes (5 cm): Six holes are recommended, two on each long side and one at each end, about 20 cm from the bottom.
   • Small holes (2.5 cm): Positioned about 4 to 5 cm above the planned substrate level. These holes ensure good air circulation.

   To avoid cracks, start by marking the hole locations, then drill a small pilot hole with a fine bit before using an appropriate hole saw. A tip is to melt the holes using a drill in "reverse" mode. This limits plastic chipping and creates cleaner edges. You can also heat a blade to melt the plastic.

   Make sure to work in a well-ventilated area and wear a mask to avoid inhaling plastic fumes.

2. Clean: Sterilize the inside and outside of the container with 70% isopropyl alcohol, as well as all your work equipment (scissors, spatulas, etc.).
3. Add a liner: Use a thick, opaque black plastic sheet to cover the bottom of the container. This reduces the tendency of mushrooms to grow on the sides of the container and makes cleaning easier. Cut the sheet so it perfectly fits the bottom dimensions, with a slight overlap on the sides.
   

Substrate Preparation

The substrate you will use depends on the species you want to grow. It can be a mix of coconut coir fiber and vermiculite, straw pellets, wood shavings, etc.

In any case, you need to moisten your substrate with the right amount of water (between 60% and 75%) and then sterilize or pasteurize it.

Example: If you have 1 kg of a coconut coir and vermiculite mix that you want to moisten to 75%, you need to add 3 kg of water for a total of 4 kg of moistened substrate. Note that the base substrate may contain a certain percentage of moisture, and it's better to add a little less water at first, then add more later if it's too dry.

For sterilization:

• In the pressure cooker : Place the moistened substrate in a heat-resistant bag and sterilize it for 90 minutes at high pressure.
• By pasteurization : Pour boiling water over the substrate placed in a container cleaned with alcohol. Cover and let cool. This will pasteurize it enough to prevent contamination. This works very well with our organic straw pellets, for example.

Once your substrate is prepared, you can move on to the next step: inoculation.

Liquid Cultures and Sterile Grains

Liquid cultures are an effective method to introduce living mycelium into your substrate. They contain mycelium fragments suspended in a sterile nutrient medium, offering faster and more uniform colonization compared to spore syringes.

Advantages of liquid cultures:

• Faster colonization because the mycelium does not need to germinate.
• Ease of use with sterile grain bags equipped with injection ports.
• Reduced risk of contamination compared to spores.

Preparation and use:

1. Sterilization : Make sure your hands, the syringe needle, and the injection ports are well cleaned with isopropyl alcohol.
2. Injection : Inject 2.5 to 5 ml of liquid culture into a bag of sterile grains via the injection port.
3. Incubation : Place the bag in a clean, dark place at a temperature between 20 and 25 °C. After 1 to 2 weeks, you can see the mycelium start to spread. At this point, you can gently shake the bag, while keeping it well sealed, to distribute the mycelium throughout the grains and speed up the colonization process. The grain should be fully colonized in 2 to 4 weeks

The colonized grain bags are then ready to be integrated into your substrate in the monotub. Some simply use our sterilized grains as a fruiting substrate (not for wood-loving mushrooms) and fruit them using the monotub box as a fruiting tent. In this case, it is not necessary to use another substrate. You just need to open the plastic bag where the mushrooms start to grow, or possibly remove the plastic completely if it is obstructive. The box will help maintain humidity. For this option, you can skip the next step of substrate incubation.

Incubation

Place the monotub in a stable and temperature-controlled environment, ideally between 20 and 25 °C, for a period of 2 to 3 weeks.

Some use heating mats to maintain a slightly higher temperature if your room temperature is insufficient.

During this phase, check your container daily. You will notice white spots gradually spreading from the inoculated grains until they completely cover the substrate surface. This indicates healthy and active growth. Drops of exudate, an amber liquid naturally produced by the mycelium, may appear on the substrate, signaling good hydration and rapid colonization.

Also watch for signs of "pin" formation: small vertical white hyphae developing into dense knots, signaling imminent fruiting. During this period, make sure humidity and temperature levels remain constant. Condensation on the lid and substrate is a good indicator of adequate hydration.

However, be attentive to molds or unusual colors, which could indicate contamination. Proactive management ensures optimal conditions for the growth and health of your mushroom culture.

The Casing Layer

Once the mycelium starts to form knots or "pins" on the substrate, it's time to add a casing layer. This layer mimics forest leaves, creating an optimal environment for mushroom fruiting.

Commonly used materials:

• Coir (coconut fiber)
• Peat
• Vermiculite (ensure it is certified asbestos-free)

Apply a thin 1 to 2 cm casing layer on the substrate and lightly moisten it using a spray bottle. The layer should be well hydrated but without excess water. Leave the lid slightly ajar to improve air exchange and reduce CO₂ accumulated.

During this period, continue to spray water daily and expose the monotub to indirect light. Although mushrooms do not photosynthesize, light is essential to guide their growth.

Mushrooms generally reach maturity one to two weeks after adding the casing layer. Harvest them before their caps are fully open for better quality and flavor.

Fruiting

Fruiting is a key stage in the mushroom cultivation cycle. Once the substrate is fully colonized, expose the monotub to indirect light to encourage fruit formation. Maintaining high humidity, between 90% and 95%, is essential to support mushroom growth.

White button mushroom cultivation

Optimal conditions:

• Humidity: Regularly spray water inside the monotub to maintain humidity. Droplets on the substrate are a good indicator.
• Ventilation: Leave the lid slightly open or drill additional holes to improve air exchange and prevent CO₂ buildup.
• Light: Soft, indirect light for about 6 to 12 hours a day helps guide mushroom growth.

Monitor fruiting: Check daily for the appearance of "pins" or young mushrooms. The first signs include white hyphae thickening into dense knots. These "pins" quickly develop into mature mushrooms within one to two weeks.

Light condensation on the walls of the container is normal and indicates adequate hydration. However, watch for signs of contamination, such as green or black mold.

Harvest: Harvest the mushrooms when their caps are still rounded and before they fully open. This ensures better quality and flavor. 

With proactive management and attentive care, the fruiting phase will result in an abundant and high-quality harvest.