A working reference for mushroom growers: symptom-first contamination diagnosis, species profiles with real numbers, substrate and process guides.https://thethirdmark.com/en-gbhttps://thethirdmark.com/diagnose/bacterial-blotch/https://thethirdmark.com/diagnose/bacterial-blotch/Sunken brown lesions on caps, a slimy film, and a smell that's clearly wrong. Bacterial blotch is a surface-water problem, and the fix is drier air rather than a treatment.Sun, 23 Aug 2026 00:00:00 GMTdiagnosehttps://thethirdmark.com/diagnose/black-mold-rhizopus/https://thethirdmark.com/diagnose/black-mold-rhizopus/Tall grey fuzz topped with black pinheads, growing fast on wet substrate. Rhizopus is not salvageable and is a genuine respiratory concern — how to identify and remove it safely.Sun, 23 Aug 2026 00:00:00 GMTdiagnosehttps://thethirdmark.com/diagnose/cobweb-mold/https://thethirdmark.com/diagnose/cobweb-mold/Cobweb mold is grey, wispy and alarmingly fast — and unlike most contaminants it's usually treatable. How to identify it, treat it, and fix the humidity problem underneath.Sun, 23 Aug 2026 00:00:00 GMTdiagnosehttps://thethirdmark.com/diagnose/long-stems-small-caps/https://thethirdmark.com/diagnose/long-stems-small-caps/Leggy, pale, stretched mushrooms with undersized caps are a fresh air problem, not a light problem. What CO₂ does to fruiting bodies and how to fix it without drying the tub out.Sun, 23 Aug 2026 00:00:00 GMTdiagnosehttps://thethirdmark.com/diagnose/mycelium-stalled/https://thethirdmark.com/diagnose/mycelium-stalled/Growth that stopped without any visible contaminant. Seven causes worth checking in order, and how long to wait before concluding it's actually dead.Sun, 23 Aug 2026 00:00:00 GMTdiagnosehttps://thethirdmark.com/diagnose/neurospora-orange-mold/https://thethirdmark.com/diagnose/neurospora-orange-mold/Bright orange powdery growth that spreads through filter patches and plastic. Neurospora is rare, unmistakable, and the only contaminant that justifies clearing a room.Sun, 23 Aug 2026 00:00:00 GMTdiagnosehttps://thethirdmark.com/diagnose/pins-aborting/https://thethirdmark.com/diagnose/pins-aborting/Pins that go clear, yellow or grey and stop growing are almost always an environmental shock rather than a disease. The five causes, in the order worth checking them.Sun, 23 Aug 2026 00:00:00 GMTdiagnosehttps://thethirdmark.com/diagnose/contamination-mid-flush/https://thethirdmark.com/diagnose/contamination-mid-flush/A block that fruited cleanly and then went green between flushes. Why post-harvest contamination happens, whether the remaining flushes are worth chasing, and how to harvest so it doesn't.Sun, 23 Aug 2026 00:00:00 GMTdiagnosehttps://thethirdmark.com/diagnose/trichoderma-green-mold/https://thethirdmark.com/diagnose/trichoderma-green-mold/Green mold in a mushroom grow is almost always Trichoderma. How to tell it from healthy mycelium, whether the tub can be saved, and what caused it.Sun, 23 Aug 2026 00:00:00 GMTdiagnosehttps://thethirdmark.com/diagnose/fruiting-sideways-in-bag/https://thethirdmark.com/diagnose/fruiting-sideways-in-bag/Mushrooms growing horizontally, curling back on themselves, or fruiting into a sealed bag. Gravity, air and light all steer a fruiting body — here's which one is steering yours.Sun, 23 Aug 2026 00:00:00 GMTdiagnosehttps://thethirdmark.com/diagnose/wet-spot-grain/https://thethirdmark.com/diagnose/wet-spot-grain/Grey-brown gluey patches, a sour smell, and mycelium that stops at the edge of them. Wet spot is bacterial, it's not treatable, and it almost always means the pressure cooker.Sun, 23 Aug 2026 00:00:00 GMTdiagnosehttps://thethirdmark.com/diagnose/yellow-liquid-metabolites/https://thethirdmark.com/diagnose/yellow-liquid-metabolites/Amber droplets on healthy mycelium are normal metabolic exudate. Yellow liquid that's spreading, smells, or sits in a puddle is not. How to tell them apart.Sun, 23 Aug 2026 00:00:00 GMTdiagnosehttps://thethirdmark.com/species/blue-oyster/https://thethirdmark.com/species/blue-oyster/The species to start with. Fast, aggressive, forgiving of technique, and it fruits at room temperature on almost anything.Sun, 23 Aug 2026 00:00:00 GMTspecieshttps://thethirdmark.com/species/king-oyster/https://thethirdmark.com/species/king-oyster/Thick-stemmed, dense, and the closest thing to a scallop in the fungal kingdom. Fussier about CO₂ than any other oyster and worth the trouble.Sun, 23 Aug 2026 00:00:00 GMTspecieshttps://thethirdmark.com/species/lions-mane/https://thethirdmark.com/species/lions-mane/A toothed, cascading fruiting body with crab-like texture. Easy to colonise, fussy to fruit well, and the most commercially valuable of the beginner-accessible species.Sun, 23 Aug 2026 00:00:00 GMTspecieshttps://thethirdmark.com/species/pink-oyster/https://thethirdmark.com/species/pink-oyster/The fastest mushroom you can grow and the only one that likes it hot. Spectacular colour, a two-week turnaround, and a shelf life measured in days.Sun, 23 Aug 2026 00:00:00 GMTspecieshttps://thethirdmark.com/species/reishi/https://thethirdmark.com/species/reishi/Grown for tea and for its appearance rather than for eating — it's too woody and bitter to be food. The one species where you choose its shape by controlling CO₂.Sun, 23 Aug 2026 00:00:00 GMTspecieshttps://thethirdmark.com/species/shiitake/https://thethirdmark.com/species/shiitake/The most demanding of the common gourmet species and the most rewarding. Long colonisation, a browning phase, and a cold shock — and then it fruits for months.Sun, 23 Aug 2026 00:00:00 GMTspecieshttps://thethirdmark.com/species/turkey-tail/https://thethirdmark.com/species/turkey-tail/Thin banded brackets found on dead hardwood worldwide. Easy to grow, impossible to eat, and the functional species with the most substantial clinical literature behind it.Sun, 23 Aug 2026 00:00:00 GMTspecieshttps://thethirdmark.com/species/wine-cap/https://thethirdmark.com/species/wine-cap/An outdoor species that grows in wood chip beds with almost no intervention. The lowest-effort mushroom there is, if you have a shaded patch of ground.Sun, 23 Aug 2026 00:00:00 GMTspecieshttps://thethirdmark.com/substrate/cvg/https://thethirdmark.com/substrate/cvg/The standard bulk substrate for monotubs. Cheap, consistent, nutritionally inert on purpose, and pasteurises with nothing more than boiling water.Sun, 23 Aug 2026 00:00:00 GMTsubstratehttps://thethirdmark.com/substrate/grain/https://thethirdmark.com/substrate/grain/Which grain to use as spawn, how they differ in practice, and why the choice matters less than getting the hydration right.Sun, 23 Aug 2026 00:00:00 GMTsubstratehttps://thethirdmark.com/substrate/hydration/https://thethirdmark.com/substrate/hydration/More grows fail on water content than on sterile technique. What field capacity means, how to test it in five seconds, and the target numbers by substrate.Sun, 23 Aug 2026 00:00:00 GMTsubstratehttps://thethirdmark.com/substrate/masters-mix/https://thethirdmark.com/substrate/masters-mix/Supplemented hardwood sawdust is the highest-yielding substrate for wood-loving species. The standard ratios, why soy hull works so well, and why it must be sterilised.Sun, 23 Aug 2026 00:00:00 GMTsubstratehttps://thethirdmark.com/substrate/sterilisation-vs-pasteurisation/https://thethirdmark.com/substrate/sterilisation-vs-pasteurisation/Which treatment a substrate needs, why, and the single rule that decides it: how much nutrition you've put in.Sun, 23 Aug 2026 00:00:00 GMTsubstratehttps://thethirdmark.com/substrate/straw/https://thethirdmark.com/substrate/straw/The cheapest bulk substrate that works, and the three ways to pasteurise it — hot water, lime bath, and cold ferment — compared honestly.Sun, 23 Aug 2026 00:00:00 GMTsubstratehttps://thethirdmark.com/process/culture/https://thethirdmark.com/process/culture/Every grow starts with a genetic starting point — a clone, a spore print, or something bought. The three routes differ enormously in how predictable the result is.Sun, 23 Aug 2026 00:00:00 GMTprocesshttps://thethirdmark.com/process/fruiting-conditions/https://thethirdmark.com/process/fruiting-conditions/Four variables — temperature, humidity, fresh air and light — and the fact that pinning is triggered by change rather than by any particular value.Sun, 23 Aug 2026 00:00:00 GMTprocesshttps://thethirdmark.com/process/agar/https://thethirdmark.com/process/agar/Growing mycelium on a clear plate is the only stage where you can actually see contamination before it costs you anything. It's also how you isolate a strain worth keeping.Sun, 23 Aug 2026 00:00:00 GMTprocesshttps://thethirdmark.com/process/grain-spawn/https://thethirdmark.com/process/grain-spawn/Sterilised grain colonised by mycelium — the multiplier that turns one culture into enough inoculum for a room of substrate. Also the stage most grows die at.Sun, 23 Aug 2026 00:00:00 GMTprocesshttps://thethirdmark.com/process/harvest/https://thethirdmark.com/process/harvest/Timing, technique, and why harvesting slightly early is almost always better than slightly late — for yield, for storage, and for the block's next flush.Sun, 23 Aug 2026 00:00:00 GMTprocesshttps://thethirdmark.com/process/colonisation/https://thethirdmark.com/process/colonisation/Two weeks of leaving it alone in the dark. What's actually happening, what to check, and why opening the tub to look is the main risk at this stage.Sun, 23 Aug 2026 00:00:00 GMTprocesshttps://thethirdmark.com/process/spawn-to-bulk/https://thethirdmark.com/process/spawn-to-bulk/Mixing colonised grain into a low-nutrition bulk substrate. Ten minutes of work that determines whether the next three weeks go well.Sun, 23 Aug 2026 00:00:00 GMTprocesshttps://thethirdmark.com/process/spent-substrate/https://thethirdmark.com/process/spent-substrate/What to do with a finished block. Some of it is genuinely useful, some of it is a way of spreading contamination around your garden, and the difference matters.Sun, 23 Aug 2026 00:00:00 GMTprocesshttps://thethirdmark.com/process/subsequent-flushes/https://thethirdmark.com/process/subsequent-flushes/Getting a second and third harvest from the same block — rehydration, timing, and the point at which chasing another flush stops being worth the risk.Sun, 23 Aug 2026 00:00:00 GMTprocesshttps://thethirdmark.com/process/liquid-culture/https://thethirdmark.com/process/liquid-culture/Mycelium suspended in sterile sugar water. Fast to inoculate with, easy to multiply, and the one stage where contamination can hide completely until it's expensive.Sun, 23 Aug 2026 00:00:00 GMTprocesshttps://thethirdmark.com/setups/pressure-cooker/https://thethirdmark.com/setups/pressure-cooker/The one piece of equipment you cannot substitute, and the most genuinely dangerous object in the hobby. Sizing, timing, and the safety points that are not optional.Sun, 23 Aug 2026 00:00:00 GMTsetupshttps://thethirdmark.com/setups/grow-kit/https://thethirdmark.com/setups/grow-kit/A pre-colonised block in a box. Realistic yields, what it does and doesn't teach you, and how to get a second flush out of one.Sun, 23 Aug 2026 00:00:00 GMTsetupshttps://thethirdmark.com/setups/sab-vs-flow-hood/https://thethirdmark.com/setups/sab-vs-flow-hood/When a $20 plastic tub is genuinely enough, and the point at which a laminar flow hood stops being a luxury. Most growers buy one too early and the other too late.Sun, 23 Aug 2026 00:00:00 GMTsetupshttps://thethirdmark.com/setups/small-commercial/https://thethirdmark.com/setups/small-commercial/Separating clean, dirty and fruiting into three spaces, and the honest arithmetic on what a small operation actually produces and costs.Sun, 23 Aug 2026 00:00:00 GMTsetupshttps://thethirdmark.com/setups/shotgun-fruiting-chamber/https://thethirdmark.com/setups/shotgun-fruiting-chamber/A perlite-filled tub drilled with dozens of quarter-inch holes. Cheap, effective for small grows, and largely superseded by the monotub — here's when it still makes sense.Sun, 23 Aug 2026 00:00:00 GMTsetupshttps://thethirdmark.com/setups/monotub/https://thethirdmark.com/setups/monotub/The standard bulk setup: a plastic tub with holes. Build dimensions, hole spacing, substrate depth, and the mistakes that turn a good tub into a CO₂ trap.Sun, 23 Aug 2026 00:00:00 GMTsetupshttps://thethirdmark.com/setups/martha-tent/https://thethirdmark.com/setups/martha-tent/A wire shelving unit in a zip-up greenhouse cover, with a humidifier and a fan on timers. The step where fruiting stops being a daily chore.Sun, 23 Aug 2026 00:00:00 GMTsetupshttps://thethirdmark.com/start/farmers-market/https://thethirdmark.com/start/farmers-market/The step where a hobby becomes a small business. Production planning, pricing, what actually sells at a stall, and the regulatory line you must not cross.Sun, 23 Aug 2026 00:00:00 GMTstarthttps://thethirdmark.com/start/first-grow-kit/https://thethirdmark.com/start/first-grow-kit/Start here if you've never grown anything. Two weeks, no equipment, and it answers the only question that matters at this stage: do you enjoy this?Sun, 23 Aug 2026 00:00:00 GMTstarthttps://thethirdmark.com/start/first-monotub/https://thethirdmark.com/start/first-monotub/Bought spawn, your own substrate, a tub with holes in it. This is where you actually learn to grow — and you still don't need a pressure cooker.Sun, 23 Aug 2026 00:00:00 GMTstarthttps://thethirdmark.com/start/grain-spawn/https://thethirdmark.com/start/grain-spawn/Making your own spawn drops your cost per tub by most of it — and introduces the pressure cooker and sterile technique. The biggest step in the progression.Sun, 23 Aug 2026 00:00:00 GMTstarthttps://thethirdmark.com/start/agar/https://thethirdmark.com/start/agar/The stage where you stop buying genetics and start keeping them. Cleaning up contaminated cultures, isolating strains, and cloning a mushroom worth repeating.Sun, 23 Aug 2026 00:00:00 GMTstart