Spawning to Monotub

Combining your colonised grain spawn with bulk substrate and starting the colonisation phase on your controller.

Before You Begin

Make sure you have the following ready before spawning:

Fully colonised grain spawn — jars should be 100% white with no visible uncolonised grain. Using partially colonised spawn increases contamination risk.
Prepared bulk substrate at field capacity — CVG, pasteurised straw, or masters mix, cooled to room temperature. See the Substrate Preparation guide.
Clean monotub — wipe the inside of your tub with isopropyl alcohol (70%) and let it dry.
Clean gloves — nitrile gloves sprayed with alcohol.
Your controller — powered on and connected, with the correct strain profile selected.

Warning: Do not spawn in a dirty or dusty room. While this step does not require a SAB (the substrate is not sterile, only pasteurised), you should still minimise exposure to airborne contaminants. Close windows, turn off fans, and work in a clean area.

Spawn-to-Substrate Ratio

The ratio of grain spawn to bulk substrate by volume affects colonisation speed and contamination resistance. More spawn means faster colonisation but uses more grain.

Ratio (Spawn : Substrate)	Colonisation Speed	Best For
1:1	Very fast (5–7 days)	When you have plenty of spawn and want fastest results. Overkill for most situations.
1:2	Fast (7–10 days)	Recommended for beginners. Good balance of speed and efficiency.
1:3	Moderate (10–14 days)	Good balance for experienced growers. Standard ratio for most grows.
1:4	Slower (14–18 days)	Maximises substrate volume per jar of spawn. Higher contamination risk for beginners.
1:5+	Slow (18+ days)	Not recommended. Contamination risk is high due to slow colonisation.

Tip: For your first grow, use a 1:2 ratio. This typically means 2–3 quart jars of grain spawn for a 54–66 qt monotub. The faster colonisation gives contamination less time to take hold.

Mixing Method (Recommended)

The mixing method distributes grain spawn evenly throughout the substrate. This creates the most inoculation points and results in the fastest, most even colonisation.

Add a base layer of substrate. Spread a thin layer (2–3 cm / 1 inch) of bulk substrate across the bottom of the tub. This ensures there is no exposed grain touching the bottom of the tub.
Break up your grain spawn. Open your colonised grain jars and break the colonised grain into individual grains or small clumps. You can do this by shaking the jar first, then using a clean spoon or your gloved hands.
Combine spawn and substrate. In the tub or in a separate clean container, mix the grain spawn and remaining substrate together thoroughly. Make sure the grain is evenly distributed — no large clumps of grain in one area.
Spread evenly in the tub. Distribute the mixed spawn and substrate evenly across the tub. Press down gently to create a flat, level surface. The total depth should be approximately 7–10 cm (3–4 inches). Thinner than 5 cm dries out too easily; thicker than 13 cm colonises unevenly.
Smooth the top. Use clean, gloved hands to gently smooth and level the surface. You want a flat, even surface for uniform pinning later.

Layering Method (Alternative)

The layering method alternates layers of substrate and grain spawn. Some growers prefer this because it keeps spawn concentrated in horizontal bands, which can produce a more even pin set.

Add a 2–3 cm base layer of substrate.
Sprinkle a layer of broken-up grain spawn evenly across the surface.
Add another 2–3 cm layer of substrate.
Add another layer of grain spawn.
Finish with a final 1–2 cm layer of substrate on top (no visible grain on the surface).
Gently press down and level the surface.

Tip: Both methods work well. The mixing method is generally faster to colonise because the spawn is more evenly distributed. The layering method can produce a slightly more even pin set on the surface. For beginners, mixing is easier and more forgiving.

Casing Layer (Optional)

A casing layer is a thin layer of non-nutritive material applied on top of the spawned substrate. It helps maintain surface humidity and creates a humid microclimate that encourages pinning.

When to Use a Casing Layer

Cubensis: Optional. Many growers get excellent results without a casing layer. If your monotub has good humidity control (which the controller provides), you may not need one.
PE (Penis Envy) and APE: Strongly recommended. These varieties benefit significantly from a casing layer.
Gourmet species: Generally not used for side-fruiting species. Not needed for oysters.

Casing Layer Materials

Pasteurised CVG — same as your substrate, just a thin layer on top.
Peat moss + vermiculite (50/50) — adjust pH to 8–9 with hydrated lime.
Bubble tek (vermiculite + water) — a simple casing of just hydrated vermiculite.

Apply the casing layer 1–2 cm thick over the surface after spawning. Do not pack it down — keep it loose and fluffy. Some growers apply the casing layer at spawning, while others wait until the substrate is fully colonised (just before triggering fruiting conditions).

Starting Colonisation on the Controller

Once your tub is spawned and sealed, it is time to start the Colonisation phase on your controller.

Close the tub. Put the lid on firmly. During colonisation, you want minimal air exchange — the mycelium needs CO2-rich conditions to colonise aggressively.
Open the controller dashboard in your browser.
Select the Colonisation phase. Navigate to your tub's controls and switch to the Colonisation phase. If you used the Setup Wizard and selected a strain profile, the correct settings will be pre-configured.
Verify settings. Typical colonisation settings for cubensis are:
- Temperature: 24–27°C (75–80°F)
- Humidity: 90–95%
- FAE (fans): Minimal — short bursts every few hours to prevent CO2 buildup from becoming excessive
Click Start. The controller will now maintain these conditions automatically.

The Waiting Game

After spawning, the hardest part is being patient. The mycelium needs time to colonise the substrate undisturbed.

Danger: Do not open the tub for at least 7–10 days after spawning. Every time you open the lid, you introduce fresh air and potential contaminants. The mycelium needs this undisturbed time to establish itself throughout the substrate. Resist the urge to peek.

What to Expect

Timeframe	What You Should See
Days 1–3	No visible change. Mycelium is recovering from being broken up and establishing in the new substrate.
Days 3–5	White mycelium visible on the surface, growing outward from grain pieces.
Days 5–7	Mycelium patches connecting and forming a network across the surface.
Days 7–10	Surface should be 70–100% colonised. Dense white mycelium covering the substrate.
Days 10–14	Full colonisation. The controller will prompt you to switch to Fruiting conditions (or auto-transition if configured).

Tip: You can check colonisation progress through the clear walls of the tub without opening the lid. Look at the sides and bottom to see how the mycelium is spreading. The controller's sensors will also show you the conditions inside the tub in real time.

Transitioning to Fruiting

When the substrate surface is 75–100% colonised with white mycelium, it is time to switch to Fruiting conditions on the controller. The controller will adjust temperature, humidity, and FAE to trigger pinning. See the Harvesting and Multi-Flush guides for what comes next.