Mushroom Substrate Calculator
Select a substrate recipe and container size. Get exact ingredient amounts scaled to your grow, with preparation instructions and spawn ratio guidance.
Field Capacity: The Most Important Variable
Regardless of recipe, your substrate must be at field capacity before mixing with spawn. Squeeze a handful firmly — a few drops of water should drip out, but not a steady stream. Over-wet substrate is the most common cause of contamination and failed grows.
- Too wet: water streams freely when squeezed → add dry vermiculite or coir
- Correct: 1–5 drops drip out, substrate holds shape
- Too dry: no water expressed, crumbles → add small amounts of water and retest
Full substrate guide → | Monotub Tek guide → | PF Tek guide →