Monotub Method

Larger-scale cultivation in plastic tubs with bulk substrate for higher yields. More setup, more harvest.

Advanced · 5-8 weeks to harvest

The monotub method scales up production using bulk substrate (coco coir, vermiculite, gypsum) colonized by grain spawn. It requires more preparation and sterile technique but yields significantly more mushrooms per grow cycle—typically 1-3 oz dried per tub.

Equipment & Supplies

• Large plastic storage tub (50–66 qt)
• Colonized grain spawn (2–4 quarts)
• Coco coir (1 brick, 650g)
• Vermiculite (2 quarts)
• Gypsum (1 cup, optional)
• 5-gallon bucket with lid
• Polyfill or micropore tape
• Drill or soldering iron (for holes)
• Spray bottle
• Digital thermometer/hygrometer
• Isopropyl alcohol (70%)
• Nitrile gloves

Step 1: Overview and Planning

A monotub is a large plastic storage tub (50-66 qt) modified with holes for air exchange. You fill it with a mix of colonized grain spawn and pasteurized bulk substrate, let it colonize, then fruit directly in the tub. One tub can yield 1-3 oz of dried mushrooms. Plan for 5-8 weeks total: 2-4 weeks for grain colonization, 1-2 weeks for bulk colonization, and 1-2 weeks for fruiting.

Step 2: Prepare Grain Spawn

Start with sterilized grain (rye berries, whole oats, or millet) in quart jars or spawn bags. Pressure cook grain at 15 PSI for 90 minutes. Once cooled, inoculate with a spore syringe or liquid culture (1cc per jar). Let colonize fully (2–4 weeks). Shake jars at 30% colonization to speed up the process and ensure even growth. Fully colonized grain—completely white with no visible grain—is your spawn.

Step 3: Prepare Bulk Substrate (CVG)

The most common bulk substrate is CVG: coco coir, vermiculite, and gypsum. Mix 650g coco coir (1 brick), 2 quarts vermiculite, and 1 cup gypsum (optional but improves structure). Pasteurize by placing in a 5-gallon bucket and pouring 4 quarts of boiling water over it. Close the lid and let sit overnight. Proper field capacity means the substrate holds moisture but doesn't drip when squeezed firmly.

Step 4: Prepare the Monotub

Drill or melt 2-inch holes in your tub: 2 holes on each long side (4 total) about 4-5 inches from the bottom, and optionally 2 holes near the top for additional FAE. Stuff holes with polyfill or cover with micropore tape. Clean the tub thoroughly with isopropyl alcohol before use.

Step 5: Spawn to Bulk

In a clean area, break up your colonized grain spawn and mix with bulk substrate at a 1:2 to 1:4 ratio (spawn to substrate). More spawn = faster colonization but higher cost. Mix thoroughly or layer (spawn-substrate-spawn-substrate). Level the surface and optionally add a thin casing layer of pure CVG on top. Close the lid and tape over all holes during colonization.

Step 6: Bulk Colonization

Keep the tub in a warm, dark place (75–80°F) for 7–14 days. The surface will turn white as mycelium colonizes the substrate. Don't open the tub during this phase—CO2 buildup is fine and actually helps colonization. The substrate is ready for fruiting when the surface is 75-100% colonized with white mycelium.

Step 7: Fruiting Conditions

Once colonized, introduce fruiting conditions: remove tape from holes (or flip/crack the lid for more FAE), provide indirect light (12/12 cycle or ambient room light), and maintain humidity by misting walls if the surface looks dry. Temperature can drop slightly to 70-75°F. Pins (tiny mushroom primordia) should appear within 1–2 weeks.

Step 8: Harvesting and Flushes

Harvest when veils begin to tear by twisting gently at the base or cutting with a clean blade. Harvest the entire flush at once for best results. After the first flush, rehydrate by pouring water on the surface and draining after 6-12 hours (or float the substrate). Subsequent flushes will be smaller but can continue for 3–5 cycles. Total yields of 1–3 oz dried per tub are common.

Tips & Common Mistakes

Pro Tips

• Master PF Tek or grain spawn before attempting monotubs.
• Use a spawn-to-substrate ratio of 1:2 for faster colonization.
• Patience during colonization prevents contamination and weak pins.
• Don't open the tub during colonization—trust the process.
• Harvest entire flushes at once for best subsequent yields.

Common Mistakes

• Attempting monotubs before mastering basic sterile technique
• Using contaminated or partially colonized grain spawn
• Opening the tub during colonization (introduces contaminants)
• Substrate too wet or too dry (should be at field capacity)
• Insufficient FAE during fruiting (causes fuzzy feet and weak pins)
• Not rehydrating between flushes (drastically reduces subsequent yields)

Frequently Asked Questions