CVG – Easy, Effective Beginner Substrate for Dung-Loving Mushrooms
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CVG — coco coir, vermiculite, and gypsum — is the most reliable, beginner-friendly bulk substrate for dung-loving mushroom species. It pasteurizes with nothing more than a kettle of boiling water, holds moisture exceptionally well, resists contamination, and produces flush after flush when prepared correctly. This guide gives you the exact ratios, the boiling water pasteurization method, the field capacity test, and a step-by-step monotub setup so you can get your grow running the same day.
What Is CVG Used For?
CVG is the standard bulk substrate for dung-loving species — primarily Psilocybe cubensis and related coprophilous fungi. It is not used for oyster mushrooms, shiitake, or other wood-loving gourmet species, which require sawdust or straw. If you are growing gourmet wood-lovers, see our CVG recipe guide for general bulk substrate, or our species-specific grow guides for substrate recommendations.
What Is CVG?
CVG stands for Coco Coir, Vermiculite, and Gypsum — three inexpensive, widely available materials that combine into an ideal mushroom substrate:
| Ingredient | Role | Where to Buy |
|---|---|---|
| Coco coir | Primary bulk material; holds moisture, resists contamination, provides structure | Garden centers, Amazon — compressed bricks or loose bags |
| Vermiculite | Improves aeration, creates air pockets, buffers moisture release | Garden centers, hardware stores — medium to coarse grade |
| Gypsum | Prevents substrate from compacting; adds calcium; improves texture | Garden centers — powdered agricultural gypsum (calcium sulfate) |
The appeal of CVG over more complex substrates like manure-based mixes is its simplicity and low contamination risk. Coco coir has a naturally low pH (~5.5–6.5) and contains antimicrobial tannins that make it inhospitable to most bacterial and mold contaminants — you can pasteurize it with boiling water alone, no pressure cooker required.
The CVG Ratio
The standard ratio for a monotub-ready CVG mix is:
Standard CVG Recipe
- 8 quarts coco coir (about half a 650g brick, fully hydrated)
- 8 quarts coarse vermiculite
- 1–2 tablespoons gypsum (powdered)
- Boiling water to field capacity (see below)
This makes approximately one standard 66-quart monotub layer (4–5 inches deep substrate).
The 1:1 coir-to-vermiculite ratio by volume is the most widely used and produces excellent results. Some cultivators use a 2:1 coir:vermiculite ratio for denser moisture retention, or add a third part field capacity-adjusted grain spawn — but for beginners the 1:1 is the reliable default.
Pasteurization with Boiling Water
CVG does not require a pressure cooker. The naturally inhospitable chemistry of coco coir combined with boiling water pasteurization (not full sterilization) is sufficient to produce consistently clean grows. Here's the process:
Expand the coco coir brick
Break your coco coir brick into a large bucket or tote. Boil a full kettle of water (or multiple kettles) and pour it directly over the coir. Use enough water to fully expand the brick — a 650g brick typically requires 4–5 liters. Break up clumps and mix thoroughly until fully expanded and evenly wetted. Let it sit 15 minutes to absorb fully.
Add vermiculite and gypsum
While the coir is still hot, add the measured vermiculite and gypsum directly to the tub. Mix thoroughly. The hot coir will pasteurize the vermiculite as they combine. Stir until uniform — the gypsum should be distributed evenly throughout, and the vermiculite should be fully integrated (not in clumps).
Cover and let it cool
Cover the tub with a clean lid or foil (not airtight — just to keep debris out) and allow to cool to room temperature. This typically takes 4–8 hours. Do not inoculate hot substrate — temperatures above 90°F will kill your mycelium. Overnight cooling is ideal. The substrate should feel warm to the touch, not hot, before you proceed.
Check field capacity
Before using your substrate, test field capacity (see below). Adjust moisture if needed, then proceed to monotub setup.
The Field Capacity Test
Field capacity is the ideal moisture level for mushroom substrate — the maximum amount of water the substrate can hold while still maintaining adequate air pockets. Too wet and you'll get anaerobic conditions and contamination. Too dry and colonization will stall.
How to test field capacity:
- Grab a handful of substrate and squeeze it firmly in your fist.
- Count the drops that fall from your hand.
- 0 drops: Too dry — add water in small amounts, mix, and retest.
- 1–3 drops: ✓ Perfect field capacity. Proceed to monotub setup.
- 4+ drops / stream of water: Too wet — spread substrate out to air-dry for 30–60 minutes, then retest.
If your CVG is too dry after cooling, simply add small amounts of room-temperature water (50–100mL at a time), mix thoroughly, and retest. If it's too wet, spread it across a clean surface in a thin layer and allow excess moisture to evaporate — this takes 30–90 minutes depending on how wet it is.
Monotub Setup with CVG
A monotub is a large, clear plastic storage tote (typically 56–66 quarts) used to colonize and fruit dung-loving mushrooms in a single uninterrupted container. CVG is the ideal substrate for monotub grows. Here's how to set one up:
Prepare your tub
Use a 56–66 quart clear or translucent storage tote. Drill 4–6 holes (about ½ inch diameter) on each long side, positioned about 3–4 inches up from the bottom — these are your fresh air exchange (FAE) ports. Stuff each hole loosely with dry polyfill (pillow stuffing) to filter incoming air without allowing contaminants. Wipe the interior with 70% isopropyl alcohol before use.
Layer spawn and CVG
Add cooled, field-capacity CVG substrate to the tub to a depth of 4–5 inches. Your colonized grain spawn (typically 1–2 quarts per tub) can be mixed throughout or layered — mixing produces faster, more even colonization. A 20–30% spawn-to-substrate ratio by volume is standard. Level the surface with a gloved hand.
Optional: casing layer
Some cultivators add a thin (½ inch) casing layer of plain coco coir on top of the inoculated substrate. The casing protects the surface, retains moisture, and can improve pinning uniformity. It is optional — many successful monotub grows skip the casing entirely.
Colonization environment
Close the lid loosely (not airtight — allow some gas exchange via the polyfill holes). Place the tub in a dark, warm location: 75–80°F is ideal for most dung-loving species. Expect full colonization (white mycelium covering the substrate surface) in 7–21 days depending on spawn vigor, temperature, and inoculation rate. Do not open the tub or disturb the substrate during colonization.
Trigger fruiting
Once the substrate surface is fully colonized, introduce fruiting conditions: raise humidity to 90–95% (mist the walls 2–3 times daily with a spray bottle — never mist directly onto the substrate surface), lower temperature slightly to 72–76°F, and increase fresh air exchange by lifting the lid briefly 2–3 times per day. Pinning typically occurs within 5–14 days of introducing fruiting conditions. Indirect ambient light or a simple LED (12 hours on/off) helps cue pinning.
Troubleshooting
| Problem | Likely Cause | Fix |
|---|---|---|
| Green mold on surface | Substrate too wet; spawn too slow; contaminated grain | Reduce moisture at field capacity next time. Isolate and discard if mold spreads past one spot. |
| Slow or patchy colonization | Cold environment; substrate too dry; low spawn rate | Move to warmer location (75–80°F). Increase spawn rate to 30% next run. |
| No pins after full colonization | Insufficient FAE; humidity too low; too warm | Fan the tub 3–4 times daily. Mist walls to raise humidity. Lower temp to 72–75°F. |
| Substrate cracking or drying out | Excess FAE; low ambient humidity | Mist the walls (not the substrate surface directly) more frequently. Reduce FAE slightly. |
| Fluffy aerial mycelium ("overlay") | Too high CO₂; insufficient FAE during colonization | Increase FAE aggressively. Fan the surface gently. The overlay can be broken up by scratching lightly with a gloved, sterile hand. |
Quick Reference Checklist
CVG Monotub Checklist
- ✓ Gather coco coir, vermiculite, gypsum, and colonized grain spawn
- ✓ Boil water and pour over coir — expand fully, let sit 15 minutes
- ✓ Mix in vermiculite (1:1 ratio) and gypsum (1–2 tbsp) while hot
- ✓ Cover and let cool to room temperature (4–8 hours or overnight)
- ✓ Squeeze test: 1–3 drops = perfect field capacity
- ✓ Prepare monotub: drill FAE holes, stuff with polyfill, wipe with IPA
- ✓ Layer or mix spawn into substrate at 20–30% by volume; level surface
- ✓ Close lid (loosely); place in warm (75–80°F), dark location
- ✓ Wait 7–21 days for full surface colonization — do not disturb
- ✓ Trigger fruiting: mist walls, add FAE, lower temp to 72–76°F
- ✓ Harvest at veil break; rehydrate and repeat for subsequent flushes
Ready to Start Your Grow?
CVG is one of the most forgiving substrates in mushroom cultivation — a great first substrate for beginners and a reliable workhorse for experienced growers.
Learn How to Make Liquid Culture →