Safety and scope
Cultivation is low-risk compared with most hobbies that involve heat and biology, but the risks it does have are concentrated in a few places worth being explicit about.
What this site covers
Cultivation of culinary and functional mushroom species — oysters, shiitake, lion's mane, king oyster, wine cap, reishi, turkey tail, cordyceps militaris and similar. Growing them, diagnosing what goes wrong, and the equipment involved.
What it does not
- Foraging and wild identification. Nothing here should be used to decide whether something found outdoors is safe to eat. Several deadly species closely resemble edible ones, and the margin for error with amatoxins is zero. Learn wild identification from local experts, in person, with specimens in hand.
- Psilocybin-containing species. Out of scope.
- Medical advice of any kind. See functional mushrooms for how research is described here and why no claims are made.
The real risks in cultivation
Pressure cookers
The most genuinely dangerous object in this hobby, and the one people are most casual about. A pressure vessel failing at 15 psi is a serious injury event.
- Check the gasket for cracking before every run.
- Keep the vent pipe clear — inspect it, don't assume it.
- Never force a lid. If it won't open, it's still pressurised.
- Do not modify the safety valve. People do this to hold higher pressure. It is the single worst idea in cultivation.
- Don't run one unattended overnight, and don't run one in a room where someone might reach for the handle without knowing what it is.
Mold spores
Contaminated substrate is a respiratory hazard, and two contaminants deserve real caution rather than routine care:
- Rhizopus and Aspergillus — capable of causing serious infection in immunocompromised people, and potent allergens in everyone.
- Trichoderma — a respiratory irritant, and heavy exposure is worth avoiding.
Wear an N95 when handling contaminated material. Seal containers before moving them, open them outdoors, and change clothes afterwards. If you are immunocompromised, pregnant, or asthmatic, hand this job to someone else — this is not an area to be stoic about.
Spore load from healthy mushrooms
Not dangerous in the acute sense, but chronic exposure to heavy spore drops causes sensitisation over time, and growers who develop it generally don't lose it. Oysters in particular produce enough spores to visibly coat a room.
Harvest before caps flatten and start dropping, ventilate the grow space, and wear a mask during harvest if you are running volume.
Allergies to the mushrooms themselves
Shiitake in particular can cause shiitake dermatitis — a distinctive whip-like rash — from eating it raw or undercooked. The compound responsible, lentinan, breaks down with proper cooking. Cook shiitake thoroughly.
More generally: cook cultivated mushrooms. Raw mushrooms are hard to digest, and several species that are perfectly good cooked cause gastrointestinal upset raw.
Chemicals
- Hydrated lime for cold pasteurisation is caustic. Eye protection and gloves, and add lime to water rather than water to lime.
- Isopropyl alcohol is flammable, and people use it next to open flames when flame-sterilising tools. Cap the bottle and move it away before lighting anything.
- Bleach and peroxide should never be mixed with each other or with ammonia-based cleaners.
Eat what you grew, not what you think you grew
Cultivation removes the identification problem almost entirely — you inoculated a known culture into a sterilised substrate — which is a large part of why it is so much safer than foraging.
The exception is outdoor beds. Wine cap beds, wood chip patches and log cultivation are open systems, and wild fungi will also fruit in them. If something appears in an outdoor bed that doesn't look like what you planted, treat it as a wild mushroom of unknown identity, which means don't eat it.