CVG Substrate Calculator
Get exact coir, vermiculite, gypsum, and water amounts for any CVG bulk substrate batch. Adjust the ratio and hydration to match your tek.
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How the formula works
CVG stands for coir, vermiculite, gypsum. It's the most common bulk substrate for gourmet and tropical mushroom species because it's clean, holds water well, and is selective enough to resist mild contamination. The math is volumetric:
- Coir = target dry volume × coir %
- Vermiculite = target dry volume × vermiculite %
- Gypsum = target dry volume × gypsum addition rate (in g per liter of substrate)
- Water = target dry volume × hydration ratio
Coir and vermiculite percentages must add to 100%. Gypsum is a small additive (typically 30 g per liter, roughly 5% of the substrate weight) that buffers pH and adds calcium for the mycelium. Hydration ratio of 1.6 is standard field capacity — squeeze a handful and you should get a few drops of water, no more.
Worked example
Target: 10 L of dry CVG at the standard 50/50 coir/vermiculite ratio, 30 g/L gypsum, 1.6× hydration.
- Coir: 10 L × 50% = 5 L
- Vermiculite: 10 L × 50% = 5 L
- Gypsum: 10 L × 30 g = 300 g
- Water: 10 L × 1.6 = 16 L
That fills roughly two 6-quart monotubs to a 4-inch substrate depth. Total wet weight will be around 21 kg.
When to use this calculator
Use this calculator any time you're prepping a fresh bulk substrate batch — whether you're running a single monotub or scaling up to multiple totes. The defaults (50/50 ratio, 30 g/L gypsum, 1.6× hydration) are the community-standard CVG recipe used by most cultivators today.
Common variations:some growers prefer 60/40 coir/vermiculite for slightly faster colonization, or 40/60 for better water retention in dry climates. If you're running a 2:1 spawn-to-bulk ratio you can typically skip gypsum entirely; the spawn carries enough buffering. The hydration ratio assumes unhydrated coir and dry vermiculite — if your coir is already partially hydrated from a brick, reduce water proportionally.
Common mistakes: not letting the coir fully expand before measuring (compressed coir bricks expand 5–7×; use the coir hydration calculator to figure out how many bricks to soak), measuring gypsum by volume instead of weight, or pasteurizing at too high a temperature and breaking the substrate down into mush.
Frequently asked questions
Do I need to pasteurize CVG?
Yes. The standard approach is hot-water pasteurization at 65–74°C (150–165°F) for 60–90 minutes, or oven pasteurization at 80°C (175°F) for 2.5 hours. Sterilization (autoclave at 15 PSI) is unnecessary for CVG and tends to make it too clean — beneficial microbes get killed off, leaving the substrate vulnerable to any stray contamination.
Can I use this for grain spawn?
No — CVG is a bulk substrate, not a grain. For grain spawn, see our grain hydration calculator.
What spawn-to-bulk ratio should I use with CVG?
1:2 (spawn to bulk by weight) is the sweet spot for most species — fast colonization, low contam risk. Use the spawn-to-bulk calculator to scale this against any bulk weight.
Why gypsum?
Gypsum (calcium sulfate) does three things: buffers pH against mycelial acidification, adds calcium that mycelium uses structurally, and slightly stiffens the substrate so it holds shape when colonizing. You can omit it for a single grow without obvious loss, but at scale it's cheap insurance.
Related resources
- Coir brick hydration calculator — Figure out how many coir bricks to soak before mixing.
- Spawn-to-bulk calculator — Match grain spawn weight to your CVG batch.
- How to set up a monotub — End-to-end tutorial that uses this exact substrate.
- Species database — Find species that fruit well on CVG.
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