How to Make Mushroom Compost: Complete Recipe and Curing Process

Mushroom compost — a byproduct of commercial mushroom farming — is a premium soil conditioner. You can replicate it at home with patience and the right ingredients.

Ingredients (Makes ~1 Cubic Yard)

• Wheat straw — 4 bales (pre-soaked 3 days)
• Horse manure — 100 lbs
• Cow manure — 50 lbs
• Chicken manure — 10 lbs
• Cottonseed meal — 50 lbs
• Molasses — 1 gallon
• Blood meal — 1 lb
• Compost activator — 1 gallon
• Calcium carbonate — 10 lbs
• Super phosphate — 1 lb
• Gypsum — 1 lb (added later)

Process

1. Soak straw 3 days (submerged). Drain — keep damp, not dry (drying kills microbes).
2. Place in large bin (dark, 3–5 ft wide/tall, tapered top). Mix all ingredients except gypsum. Moisture: damp, not soggy.
3. Pile loosely for air pockets. Let stand 6–7 days.
4. Check core temp: 150–180°F = active curing. White fungus (Actinomycetes) = good sign.
5. When temp drops, turn pile, add water if needed, restack. Repeat until stable.
6. After ~1 week, add gypsum, mix thoroughly. Rest 5 days, turn again.
7. Final mix: blackish-brown, white fungus throughout, pH 7.0–7.5, earthy smell.
8. Pasteurize: 140°F for 4 hours in oven (covered). Cool covered. Uncover only when adding spawn.

Reality Check

This takes 3–4 weeks of active management. For immediate planting, buy bagged mushroom compost. But homemade lets you control inputs and learn the biology.