Mushroom Growing Chambers:
SGFC, Monotub & Martha Tent Guides

Tote Size Selection

Monotub Setup — Step by Step

• 1Choose your tote and drill FAE holes before anything else. See Section 04 for the correct hole configuration. Clean the tote with 70% isopropyl alcohol and allow to dry completely.
• 2Prepare bulk substrate to field capacity. For CVG (coco coir, vermiculite, gypsum): mix 1 brick coco coir + 2 qt vermiculite + 1 tbsp gypsum, hydrate with 2 qt boiling water, allow to cool. For straw: pasteurize at 160–185°F for 1–2 hours, drain thoroughly, and cool to room temperature. Test field capacity: squeeze a handful — 0–5 drops of water means correct hydration.
• 3Inoculate with colonized grain spawn at 10–20% by volume. Mix thoroughly — grain spawn should be evenly distributed throughout the bulk substrate, not layered on top. Work in a cleaned area with gloves and mask.
• 4Fill tub to 3–4 inch substrate depth, level the surface, and cover with the lid. During colonization, keep the lid mostly closed — the tub maintains its own internal humidity. Store at 70–75°F in a dark location.
• 5Wait for full colonization (white mycelium covering all visible substrate surface — typically 7–14 days for oyster, 14–21 days for other species). Do not disturb during colonization.
• 6Initiate fruiting: Move to your fruiting temperature range, crack or remove the lid as appropriate for your FAE configuration, and begin 2–3 daily mistings of the tub walls. Pins typically appear within 5–10 days.

What Is Field Capacity?

Field capacity is the point at which substrate holds maximum moisture without pooling — the correct hydration for both colonization and fruiting. Test by squeezing a handful firmly: 0–5 drops = correct. No water = too dry. Stream of water = over-saturated. The feel should be like a wrung-out sponge — damp throughout but not wet. Substrate that is too wet will compact, restrict gas exchange, and promote bacterial contamination. Adding water after colonization has begun is difficult and disruptive — get field capacity right before inoculation.

Approach Comparison

Tek-Style Build — Specific Instructions

• Hole size: 1.5–2 inches — large enough for adequate gas exchange; small enough that polyfill stays packed without falling through
• Location: upper third of all four side walls — 2–4 holes per side, positioned above the substrate surface level so air exchange happens above the growing medium
• Polyfill packing: stuff firmly but not compacted — loose polyfill allows air to move freely while catching most airborne particles; over-packed polyfill restricts FAE
• Lid position during fruiting: partially cracked or removed — the top of the tub needs air exchange too; many growers remove the lid entirely and place a layer of polyfill on top of the substrate after pinning begins

Component List

Martha Tent Workflow

• 1Colonize blocks separately in a separate incubation area at 70–75°F. The Martha tent is not used during colonization — only for fruiting. Colonize in grow bags, filter patch bags, or covered trays until fully white.
• 2Set humidity controller setpoints: lower setpoint 85% (humidifier activates below this), upper setpoint 93–95% (fan activates above this). This creates automated oscillation between 85–95% RH.
• 3Load fully colonized blocks onto shelves with X-cuts or openings facing inward toward the tent interior. Space blocks so air can circulate around all sides.
• 4Monitor for the first 48 hours after loading — verify hygrometer readings match setpoints, check for any blocks showing contamination that may have been missed, and ensure the fan cycles are providing adequate FAE.
• 5Run a rotating production cycle: as blocks finish their final flush and are removed, replace with newly colonized blocks from your incubation area. A well-managed Martha tent can run continuously year-round.

Humidity Targets by Growth Phase

How to Automate Humidity in a Martha Tent

A two-stage humidity controller (Inkbird IHC-200 is the standard home cultivation choice) operates two separate outlets based on a single RH sensor reading. Plug your ultrasonic humidifier into the lower outlet and set it to activate when RH drops below 85%. Plug your small fan into the upper outlet and set it to activate when RH exceeds 93–95%. The controller creates an automated oscillation between 85–95% — when humidity gets too low, the humidifier runs; when it gets too high, the fan runs (which also provides FAE simultaneously). The probe should be positioned at mid-tent height at the level of your fruiting blocks — not near the ceiling where RH reads higher than the actual growing zone.

Why FAE Matters

Mushroom mycelium continuously produces CO₂ during both colonization and fruiting. In a sealed chamber, CO₂ accumulates and reaches concentrations that suppress normal cap development — mushrooms elongate toward the source of fresher air (openings, vents) rather than developing broad caps. Adequate FAE keeps CO₂ below approximately 1000 ppm in the fruiting zone, allowing normal development. The symptom of poor FAE is always the same: long, thin stems and small or misshapen caps.

FAE by Chamber Type

The Three Purposes of Ventilation

• CO₂ removal: The primary functional purpose — removes metabolic CO₂ that inhibits normal fruiting body development
• Contamination prevention: Moving air prevents stagnant humid pockets where mold spores settle and germinate; good FAE is one of the most effective contamination prevention measures
• Humidity regulation: When paired with a humidity controller, the fan provides humidity correction (removing excess moisture) simultaneously with FAE — two functions from one device

Passive Convection Positioning

For passive vent positioning: place lower vents near the bottom and upper vents near the top of the chamber. Warm, CO₂-rich air naturally rises and exits through upper openings while cooler, denser fresh air enters through lower openings — a natural convection loop that works without a fan. This principle applies to SGFC holes, monotub hole placement, and Martha tent vent positioning.

What Light Actually Does for Mushrooms

Unlike cannabis or most plants, mushrooms don't photosynthesize — they have no use for light as an energy source. Light serves two functions in mushroom cultivation: it provides a directional cue (mushrooms grow toward light, which results in caps orienting toward the light source) and it acts as a weak environmental signal indicating the mycelium has reached an above-ground, open-air position suitable for fruiting body development. The specific light-to-dark ratio is not critical — what matters is providing consistent, indirect illumination so mushrooms don't grow sideways toward your room's only window.

Practical Lighting Recommendations

• Ambient room light is sufficient for most grows: If your fruiting chamber is in a room that gets normal daylight or has standard ceiling lighting used for 10–16 hours daily, no supplemental lighting is needed
• For chambers in dark closets or basements: A T5 fluorescent or LED shop light (6500K color temperature) provides appropriate indirect illumination; a simple plug-in timer for 12–16 hours on is adequate
• Position for uniform indirect coverage: Light from the side or above; avoid positioning lights so they create a strong directional gradient (mushrooms will lean noticeably toward a single-sided light source)
• Low intensity preferred: Mushrooms don't need and aren't helped by high light intensity — a 40W equivalent LED providing general illumination is more than adequate; grow lights designed for cannabis or plants are unnecessary and will dry out your chamber faster from the heat they generate

Prevention Checklist

• Sterilize high-nutrition substrates completely: Grain and supplemented sawdust require 250°F/15 PSI pressure cooking for 2.5+ hours — inadequate sterilization is the most common Trichoderma entry point
• Clean the chamber before loading: Wipe all surfaces with 70% isopropyl alcohol or an Effectant solution and allow to dry before placing any blocks
• Inspect blocks before loading into a Martha tent: A contaminated block loaded into a shared chamber will spread spores to every other block on the next fan cycle — inspect each block individually before placing it in the tent
• Maintain FAE: Stagnant, humid air pockets are where contaminant spores settle and germinate; consistent FAE is one of the most effective passive contamination controls
• Wear clean gloves and minimize physical contact: Skin oils and the natural bacteria on hands are contamination vectors; nitrile gloves during any substrate handling reduce this risk significantly

Safe Contamination Removal — The Containment Protocol

• 1Before touching the contaminated block, have a clean plastic bag ready. Do not touch the block, move it, or examine it closely before the bag is available — Trichoderma releases spores when physically disturbed.
• 2Place the clean bag over the contaminated block while it is still on the shelf or in the chamber — slide the bag down over it rather than lifting the block toward the bag. The block should be inside the sealed bag before it leaves its position.
• 3Seal the bag and carry the contained block out of the grow space immediately. Do not set it down inside the chamber, next to other blocks, or on any surface that will contact future substrate.
• 4Dispose of the sealed bag outdoors. Do not open the bag to examine the contamination or compost the contents indoors.
• 5Clean and sanitize all surfaces the contaminated block contacted with 70% isopropyl or Effectant solution — the shelf surface, any walls it may have touched, and your gloved hands.

Sanitation Products

• 70% isopropyl alcohol: Standard surface sterilizer; use in spray bottle or as wipes; allow to dry completely before placing substrate (wet IPA can inhibit mycelium)
• Effectant disinfectant: Mushroom-safe broad-spectrum disinfectant; dilute per instructions; leaves no harmful residue after drying; recommended for chamber interior surfaces
• Avoid bleach solutions inside grow chambers: Bleach off-gassing in an enclosed environment can inhibit mycelium; use only for cleaning external surfaces and equipment between grows, not inside an active fruiting chamber

Reuse Potential by Species and Substrate

Chamber Maintenance Between Cycles

• 1Remove all spent substrate, stubble, and organic debris from the chamber interior. Any organic matter left behind is a contamination seed for the next cycle.
• 2Wipe all chamber surfaces with 70% isopropyl or Effectant. For Martha tents, wipe down all shelf surfaces, the tent interior, and the humidifier housing. For monotubs, scrub the interior with soap and water, rinse, then wipe with IPA.
• 3Allow to dry completely before loading the next batch — wet IPA or residual moisture creates an unfavorable surface for mycelium.
• 4Inspect all equipment: clean humidifier water tank and nozzle (mineral buildup reduces output), check fan blades for residue, replace hygrometer batteries if low, and inspect polyfill in monotub holes for compression or contamination.

Cold Shock Protocol

• 1Wait for the block to fully colonize and "set" — fully colonized shiitake blocks turn brown and harden. This hardening is the final stage before fruiting readiness. Do not initiate cold shock before the block is fully brown and firm.
• 2Submerge the block in cold water (35–50°F / 2–10°C) for 12–24 hours. Use a cooler with ice packs if your tap water isn't cold enough. The temperature drop mimics seasonal transition and is the primary fruiting trigger for shiitake.
• 3Move to fruiting conditions immediately after cold shock: 55–65°F, 85–95% RH, strong FAE, indirect light 12–16 hours. Pins typically emerge within 5–7 days.
• 4If no pins appear after 10–14 days — repeat the cold shock. Multiple cold shock cycles are normal for subsequent flushes on the same block.