Monotub Substrate Calculator
Calculate substrate ratios, grain spawn amount, and tub capacity for monotub mushroom cultivation.
Covers CVG and manure substrates for oyster and cubensis.
A monotub is a large plastic tub used for bulk mushroom cultivation. The substrate fills the tub to a depth of 3–5 inches and consists of colonized grain spawn mixed with a bulk substrate (typically pasteurized coir, straw, or manure-based mixes).
Core Formula: Total Substrate Volume = Tub Length × Tub Width × Substrate Depth
Spawn-to-Substrate Ratio: The ratio of colonized grain spawn to bulk substrate significantly affects colonization speed and contamination resistance.
| Ratio (Spawn:Sub) | Colonization Time | Contamination Risk | Spawn Cost |
|---|---|---|---|
| 1:1 | 7–10 days | Very low | High |
| 1:2 | 10–14 days | Low | Medium |
| 1:3 | 14–21 days | Moderate | Low |
| 1:4 | 21–28 days | Higher | Lowest |
| 1:5 | 28+ days | High | Minimal |
The recommended ratio for beginners is 1:2 (one part spawn to two parts bulk substrate by volume). Experienced growers can stretch to 1:3 or 1:4.
Bulk Substrate — CVG Recipe (Coir-Vermiculite-Gypsum): Per 1 quart of substrate:
- Coco coir: 1 brick (650 g) makes ~8–9 quarts hydrated
- Vermiculite: 2 quarts per brick of coir
- Gypsum: 1 cup per brick of coir
- Water: 3–4 quarts per brick (field capacity)
Worked Example — 66-quart monotub, 4-inch depth, 1:2 ratio:
- Tub interior: ~24" × 16" = 384 in²
- Substrate depth: 4 inches
- Volume: 384 × 4 = 1,536 in³ ÷ 57.75 = 26.6 quarts total
- Spawn (1:2): 26.6 / 3 = 8.9 quarts grain spawn
- Bulk sub: 26.6 × 2/3 = 17.7 quarts CVG substrate
- Coir needed: ~2 bricks
- Vermiculite: ~4 quarts
- Gypsum: ~2 cups
Yield Expectations: A well-colonized monotub typically produces 1–3 flushes. First flush is the largest. Expected yield for oyster mushrooms: 1–2 lb per flush. For cubensis-type: 1–3 oz dry per flush from a 66-qt tub.
Substrate Depth Guide:
- 3 inches: faster colonization, lower total yield
- 4 inches: balanced (recommended)
- 5 inches: higher yield potential but slower colonization and increased contamination risk
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.