CVG Substrate Calculator
Coir, Vermiculite & Gypsum
Calculate water needed to reach field capacity for monotub and bulk coir-based grows.
Typical 650g brick
2000 ml ~ 200g dry expanded vermiculite
Target moisture: 67% — Field capacity (squeeze test: 1-3 drops)
Method: Pour boiling water over ingredients in a sealed bucket. Wait 2-4 hours until cooled to room temperature.
Results are estimates. Actual values vary by ingredient brand and moisture content.
When to Use This Calculator
Use the CVG calculator whenever you are preparing bulk substrate for monotub grows, shoebox tek, or any coir-based fruiting setup. CVG (coco coir, vermiculite, and gypsum) is the most popular bulk substrate for beginners because it only requires pasteurization — no pressure cooker needed. This calculator ensures you hit field capacity every time by accounting for the existing moisture in each ingredient, so you never end up with a soggy or dry tub.
Tips for Best Results
- •Always use boiling water when hydrating your CVG mix — this pasteurizes the substrate and kills competing organisms without a pressure cooker.
- •Seal your bucket with a tight lid and let it sit for 2-4 hours. The trapped steam completes pasteurization while the substrate cools to a safe temperature.
- •Always perform the squeeze test after cooling: grab a handful and squeeze firmly. You should see 1-3 drops of water — no more. If water streams out, the substrate is too wet.
- •Coir brands vary significantly in moisture content. Compressed bricks from different manufacturers may need more or less water, so adjust the moisture slider if you know your brand runs wetter or drier.
- •Only add spawn once the substrate has cooled to room temperature (below 27°C / 80°F). Adding spawn to hot substrate will kill the mycelium.
- •Vermiculite adds both water retention and air pockets to the substrate, improving moisture regulation and gas exchange throughout the colonization period.
- •Gypsum (calcium sulfate) serves two purposes: it prevents the coir from clumping into dense mats, and it provides calcium that supports healthy mycelial growth.