Manure-Based Substrate Calculator
Get exact composted-manure, coir, vermiculite, gypsum, and water amounts for any dung-loving species batch.
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How the formula works
Manure-based substrate is the standard bulk mix for dung-loving species. The math is by volume — manure replaces roughly half the substrate that coir would normally fill in a CVG-style mix:
- Manure volume = total volume × manure %
- Coir volume = total volume × coir %
- Vermiculite volume = total volume × vermiculite %
- Gypsum = total volume × gypsum g/L
- Water = total volume × hydration ratio
Manure, coir, and vermiculite percentages must add to 100. The big difference vs a plain coir-vermiculite-gypsum (CVG) mix: manure replaces ~half the substrate volume and brings the high-nitrogen, partially-digested cellulose environment that dung-loving species evolved on. Coir and vermiculite still pull their usual jobs — moisture retention and air gaps — but the manure is what makes the substrate actually selective for these species.
Worked example
Target: 10 L of dry manure substrate at the standard 60/30/10 ratio (manure / coir / vermiculite), 30 g/L gypsum, 1.5× hydration.
- Manure: 10 L × 60% = 6 L
- Coir: 10 L × 30% = 3 L
- Vermiculite: 10 L × 10% = 1 L
- Gypsum: 10 L × 30 g/L = 300 g
- Water: 10 L × 1.5 = 15 L
That fills a standard 6-quart monotub comfortably. Pasteurize the dry mix in a sealed bag or container at 65–74°C for 60–90 minutes, cool to room temperature, then spawn at 1:2 to 1:3 (grain spawn to substrate by volume). Cased with another centimeter of pasteurized coir, dung-loving species typically pin in 7–14 days post-spawn under warm fruiting conditions.
When to use this calculator
Use this calculator any time you're prepping bulk substrate for dung-loving species. Panaeolus cyanescens, the Copelandia group, and several Psilocybe species (including P. cubensisin some recipes) evolved on grazing land — cattle, water buffalo, and horse pastures — and their mycelium depends on partially-digested cellulose plus the nitrogen and minerals that survive a ruminant's gut. A coir-only mix will fruit some of these species but yields are a fraction of what a proper manure substrate produces, and pinning is unreliable.
Composted only — never fresh.Fresh manure carries ammonia, weed seeds, and aggressive bacteria that out-compete mycelium and stall colonization for weeks. You want it aged at least 6 months, ideally a year, until it smells earthy rather than barn-y. If it still smells like ammonia, it's not done.
Horse vs cow vs goat: horse manure is the community favourite — drier than cow, fewer weed seeds (horses are less efficient digesters than ruminants, but the seeds tend to be less viable), and easier to source clean from stables that compost their own. Cow works but tends to be wetter and weedier. Goat is excellent if you can find it — small dry pellets, low ammonia — but local supply is hit-or-miss.
Pasteurize, don't sterilize. Manure substrates use the same pasteurization profile as CVG: 65–74°C for 60–90 minutes, in a sealed container or insulated cooler with hot water. Sterilization (15 PSI / 2.5 hours) wipes out the beneficial thermophilic bacteria that keep the substrate selective and actually makes contamination worse, not better, for bulk mixes.
Where to source: bagged composted horse manure from garden centers (look for OMRI-listed, no added fertilizer or herbicides), or local stables that compost their own — many will give it away free if you bring buckets. Avoid manure from pastures treated with persistent herbicides like aminopyralid, which can survive composting and inhibit fungal growth.
Frequently asked questions
Where do I get clean horse manure?
Local stables that compost their own bedding are the best source — most will give you composted manure for free if you ask and bring buckets. Look for stables that don't treat pastures with aminopyralid or other persistent herbicides. As a backup, bagged composted horse manure from garden centers works (look for OMRI-listed, no added fertilizer). It should smell earthy, not barn-y or like ammonia.
Can I use bagged composted manure from a garden center?
Yes, if it's fully composted (not "steer manure compost blend" with a bunch of fillers) and free of added fertilizer or herbicide. OMRI-listed bags are safest. Sift out any large chunks, pasteurize as normal, and you're good. Skip anything labelled "humus" or "manure compost" without a clear ingredient list — that's usually a soil amendment with too much filler to fruit on.
Why pasteurize manure substrates?
Pasteurization (65–74°C for 60–90 minutes) kills the molds and aggressive bacteria that would out-compete mycelium, while leaving the beneficial thermophilic bacteria that keep the substrate selective. Sterilization makes the substrate too rich for selectivity — anything that lands on it from the air will take over before mycelium can. This is the same logic as CVG and straw substrates.
Does this work for non-dung-loving species?
Not well. Wood-loving species (lion's mane, oyster, shiitake, chestnut) want a hardwood-based substrate — see the Master's Mix calculator. Tropical species and most gourmets do well on plain CVG — see the CVG calculator. Manure substrate is specifically for species that evolved on grazing land.
Related resources
- CVG substrate calculator — For tropical species and most gourmets.
- Coir hydration calculator — Hydrate coir bricks before mixing.
- Spawn-to-bulk calculator — Match grain spawn weight to your batch.
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