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Under-filled tubs dry out; over-filled tubs stall. Enter your container size below to get a scaled coir, vermiculite and gypsum recipe with the right spawn rate and an estimated water amount for field capacity.
Substrate amounts by container size
| Container | Dry coir brick | Vermiculite (dry) | Gypsum | Grain spawn (10–20%) |
|---|---|---|---|---|
| 6 qt shoebox (~2–3 in deep) | ~150 g | ~1.5 qt | ~2 tbsp | ~0.5–1 qt jar |
| 32 qt monotub (~3–4 in deep) | ~325 g (half brick) | ~3 qt | ~4 tbsp | ~1–2 qt jars |
| 66 qt monotub (~3–4 in deep) | ~650 g (full brick) | ~6 qt | ~8 tbsp | ~2–4 qt jars |
These follow the common 1 : 1 : small-gypsum style CVG ratio by volume, hydrated to field capacity (a squeezed handful drips a few drops). Higher spawn rates colonize faster and resist contamination but cost more spawn. Always pasteurize or sterilize according to your recipe’s method and let the mix cool before spawning.
FAQ
What spawn rate should I use?
10–20% grain spawn to wet substrate weight is standard. Use the high end for nutritious mixes and the low end for plain coir or straw.
How wet should the mix be?
Field capacity: squeeze hard and only a few drops appear. A steady stream means too wet — squeeze out or add dry vermiculite.
Do I need gypsum?
It adds calcium and structure and is cheap insurance, but coir and vermiculite alone still fruit. Keep it under about 5% of dry weight.
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