How much grain spawn do I need for a monotub?

A common ratio is 1 part grain spawn to 2–3 parts bulk substrate by volume. For a 66-litre tub you typically use 2–3 kg of colonised grain spawn mixed with 6–9 kg of prepared bulk substrate like coco coir and vermiculite.

How deep should the substrate be in a monotub?

Aim for a substrate depth of 10–15 cm (4–6 inches). Deeper substrate retains more moisture, supports more flushes, and produces bigger mushrooms but also increases contamination risk if not managed well.

Can I reuse a monotub substrate?

A well-managed monotub can produce 3–5 flushes before yields decline significantly. Between flushes, dunk the substrate in cold water for 12–24 hours to rehydrate, then resume fruiting conditions. After the final flush compost the spent substrate.

📏 Monotub Spawn Calculator

Calculate the perfect amount of grain and substrate

Tub Size (Quarts)

Spawn to Substrate Ratio Recommended: 1:2 for beginners.

Target Depth (Inches) Standard is 3-4 inches.

Grain Spawn Needed

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Substrate Needed

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Total Mix Volume

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📊 Visual Ratio:

Note: These are estimates. Tub dimensions vary by brand (Sterilite vs Rubbermaid). It's better to have slightly too much substrate than too little.

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