What Is Trichoderma?

Trichoderma (also called Trich or green mold by some) is infamous in the mushroom growing community. Whether the green mold is in your grow is in your substrate or on your grain spawn, it's known as a pernicious problem for some growers. So, what is it?

Simply put, Trichoderm is a fast‑growing filamentous fungus. It's responsible for the classic “green mold” that attacks mushroom cultures and substrates. It usually starts as white mycelium and then turns a bright, powdery green as it sporulates across grain, compost, or bulk substrate. In mushroom cultivation, Trichoderma is considered a major pathogen because it directly competes with and can chemically attack mushroom mycelium, leading to stalled colonization, reduced yields, and full crop loss. Home growers most often encounter it in grain spawn, monotubs, grow bags, and on casing or bulk substrates during colonization or early fruiting.

Why Green Mold Appears

Trichoderma spores are everywhere, unfortunately. They're on clothes, tools, dust, soil, and even in house air, so contamination happens when conditions favor the mold more than the mushroom. Common triggers include under‑sterilized or poorly pasteurized substrate, dirty grow spaces, weak or contaminated spawn, and overly wet, stagnant microclimates. If you focus on keeping clean and balanced then Trich will be less likely to take root.

Once Trichoderma spores land on a nutrient‑rich, moist surface at a suitable temperature, they germinate quickly and can overrun a tray, bag, or monotub within 48–72 hours. Since sporulation releases vast numbers of new spores into the grow room, a single neglected tub can seed recurring green mold outbreaks across multiple future grows. Basically, it can kill your whole set up really fast.

Avoiding Trichoderma

With Trichoderma being such a pernicious issue, it's important to take these strategies whenever you're growing mushrooms. This advice is regardless of variety of mushroom or the 'strain' so these are useful things to know and memorize for future use.

The High‑Risk Stages In A Grow

Trichoderma can strike at any point, but some stages are especially vulnerable. Grain jars or bags are high risk if grain is under‑cooked, under‑sterilized, or inoculated with dirty culture, since they offer dense nutrition in a confined space. Bulk substrates and monotubs are also common points of failure because they expose a large nutrient surface to air and handling during spawning and mixing.

In addition to this, grow bags and trays in incubation can hide contamination until it suddenly breaks through the surface as green mold, particularly when there are wet pockets, anaerobic zones (low air circulation), or uncolonized substrate left sitting too long. Early fruiting is another window where excess humidity, poor fresh air exchange (FAE), and puddling water can push the balance in favor of Trichoderma instead of mushroom mycelium.

Clean Spawn And Substrate

Starting with clean, vigorous spawn is another line of defense against Trichoderma. Good spawn should be fully colonized, bright white, and free of wet, slimy, or discolored patches that signal bacterial or mold issues. Any jar or bag showing green, gray, or stalled “wet” areas should be discarded rather than mixed into bulk substrate, since one contaminated unit can spread spores through an entire grow room. It's better to be safe than sorry!

Substrate treatment is equally critical: research on green mold in lignocellulosic substrates shows that proper hot‑water or alkaline treatments significantly reduce Trichoderma growth during spawning. For bulk materials like straw, coir, and sawdust, reliable options include pasteurization around 60°C for at least 30 minutes, hot‑water immersion, or soaking in an alkalinized solution long enough to raise pH above mold‑friendly levels.

Sterile Technique During Inoculation

Inoculation is where many “mystery” Trichoderma problems actually begin. Opening sterile grain or substrate in a dusty room, talking over open containers, or reusing unclean tools gives mold spores an easy entry point. A simple still air box or laminar flow hood, combined with disinfected work surfaces and tools, dramatically lowers contamination risk in grain transfers and monotub spawning.

Before each sterile session, surfaces should be wiped with isopropyl alcohol or a suitable disinfectant, tools flame‑sterilized or alcohol‑wiped between jars, and fans or HVAC vents turned off to minimize moving air over open vessels. Hands should be washed, gloves and a mask are recommended, and pets or bystanders should be kept out of the room while spawn, agar, or liquid culture is exposed.

Grow Room Hygiene & Layout

A clean, well‑planned grow space is at the heart of preventing recurring Trichoderma contamination. Dedicated “clean” zones for lab work or inoculation should be kept separate from “dirty” zones where bulk substrate is mixed, waste is stored, or fruits are harvested. Regular cleaning of walls, benches, shelving, and floors with disinfectant or mild bleach solution keeps spore loads down and prevents mold from establishing hidden reservoirs.

Outdoor clothing, potting soil, compost, and houseplants are all common sources of Trichoderma and should be kept away from the grow room to avoid constant re‑introduction of spores. Equipment such as humidifiers, fans, and filters needs periodic deep cleaning, since biofilm and dust buildup on these devices can turn them into efficient mold spreaders.

Dialing In Conditions (Monotubs, Bags, Rooms)

Environmental control is where prevention meets performance. Trichoderma thrives in warm, stagnant, overly wet conditions, so the goal is to provide each species with its ideal temperature and humidity while avoiding standing water and poor airflow. For many common indoor species, colonization around 21-25°C and high but not dripping humidity during fruiting strikes a good balance between fast mycelial growth and reduced mold pressure.

In monotubs and grow bags, good FAE is essential: too little exchange leaves CO2 and moisture trapped, creating mold‑friendly microclimates, while harsh direct drafts can dry out substrates and blow spores around the room. Properly sized filter patches, synthetic filter discs, poly‑fill, or micro‑pore tape over vents help maintain air exchange while filtering out a large share of airborne Trichoderma spores.

Spotting & Handling Trichoderma Early

Early identification and aggressive containment often determine whether a Trichoderma incident is a minor hiccup or a full reset. Typical signs include white mycelium that turns dull and then bright green, especially in circular or patchy zones, often accompanied by a dusty look as spores form. A musty or earthy off‑odor, compared with the clean mushroom smell of healthy mycelium, is another warning that green mold may be present.

Once green spores are visible on a jar, bag, or monotub, the safest move is to seal it and remove it from the grow area immediately rather than trying “surgery” inside the room. Articles aimed at home growers consistently advise disposing of heavily contaminated units, then sanitizing nearby tools, shelving, and tubs with bleach or other strong disinfectants before starting a new cycle.

pH And Casing Strategies

Adjusting substrate and casing pH can make the environment less inviting for Trichoderma while remaining suitable for mushrooms. Green mold species tend to favor slightly acidic conditions in the pH 4-6 range, whereas many cultivated fungi tolerate more neutral or mildly alkaline substrates. Techniques such as soaking substrate in alkalinized water or using buffering agents to raise pH have been shown to reduce Trichoderma growth during spawning and colonization of lignicolous species.

For some setups, a non‑nutritive, pH‑adjusted casing layer based on peat and vermiculite can act as a physical and chemical barrier that holds moisture for the mushrooms while being less attractive to molds. Growers experiencing frequent green mold outbreaks sometimes “reboot” surface pH between flushes by adding a fresh, thin casing layer rather than scraping the old one, helping protect the underlying mycelium from new Trichoderma spores.

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When To Reset Your Grow

If multiple tubs, bags, or shelves go green in close succession, the problem is usually systemic: high spore load in the room, dirty equipment, or contaminated spawn or substrate batches. In these cases, isolating individual tubs is rarely enough; most experienced cultivators recommend halting production, discarding suspect materials, and performing a top‑to‑bottom cleaning before the next run.

A proper reset includes thoroughly cleaning or replacing filters and hoses, disinfecting walls and ceilings reachable in the grow area, and reviewing each step in the workflow. This means focusing on each step from culture to inoculation to fruiting, to pinpoint where Trichoderma is most likely entering. Pairing this with a known‑clean spawn source and carefully treated substrate drastically improves the odds that the next grow remains Trich‑free.

Trichoderma Prevention Checklist

• Spawn: Only use fully white, vigorous grain spawn with no wet, sour, or discolored spots; discard anything suspicious.
• Substrate: Pasteurize or otherwise treat straw, coir, and other bulk substrates using proven time/temperature or alkaline methods.
• Sterile work: Inoculate in a still air box or in front of a flow hood; sanitize tools and surfaces before and during use.
• Environment: Keep the grow room clean, control humidity and FAE in monotubs and grow bags, and avoid standing water or stagnant corners.
• Monitoring: Check grows daily for early white‑to‑green patches and off smells, isolate any suspect container immediately, and clean the surrounding area after removal.