🍄 Spawn Run to Harvest

You spawned the bag. Now nothing appears to happen for two to four weeks. This lesson is about what is actually going on in that time, how long it should take, and how to tell a normal slow batch from a batch that is failing.

What is happening is colonisation, also called the spawn run. Mycelium from the spawn grows out of each grain and through the whole substrate mass, secreting enzymes that digest the straw or sawdust externally and then absorbing what it has digested. It converts loose, damp substrate into a solid, white, bound block. You can see it happening from the outside: white threads spreading out from each spawn grain, joining up, and eventually covering everything.

Remember what you are actually growing. You are not growing a mushroom. You are growing mycelium, and later you will harvest its fruit. Everything you do at this stage is a decision about mycelial health.

What conditions does the spawn run want? Warm and dark. The Botswana production guide gives 25-30 degrees C and complete darkness, with the bag covered in black plastic. MushWorld gives 25 degrees C. The Nigerian Akure trial ran colonisation at 26 plus or minus 1 degree C. Room humidity barely matters, because the substrate is inside a sealed or lightly vented bag holding its own moisture. High carbon dioxide inside the bag is fine and even helpful at this stage. Leave the bags alone. Do not open them to look. The only handling they need is a routine visual check from the outside for green, black, pink or orange patches.

Now the timings, and there is real disagreement between the sources, which you should understand rather than ignore.

• Botswana production guide: 14-35 days, average 28 days.
• MushWorld handbook: 12-15 days to substantial colonisation, 20-21 days until the mycelium has spread completely through the bag.
• Ethiopian trial at Hawassa: 14 days on cotton seed hull and paper waste, the fastest, out to 19.67 days on sawdust, the slowest.
• Nigerian trial at Akure: 14.3-25.0 days depending on species and substrate.

The spread across those four sources runs from 12 to 35 days, and that spread is real. It is not one source being wrong. It reflects genuine differences in substrate, spawn rate, ambient temperature and strain. Notice in particular the Ethiopian result: cotton seed hull colonised in 14 days and sawdust took 19.67 days in the same trial under the same conditions. Substrate choice is itself one of the biggest levers on how fast your spawn run finishes.

So how do you use these numbers? Not as a deadline. Use them to build your own baseline. After three or four batches you will know what your substrate, your spawn and your room normally do - say 18 days, or 24. That personal figure is worth more than any of the four published ranges, because it is measured on your own operation.

And then use your baseline as an alarm. A batch running unusually slowly compared with your own past experience is an early warning sign worth investigating, not something to simply wait out. The likely causes, in the order worth checking: weak or old spawn, substrate moisture wrong, temperature too low, or substrate nutrition poor for the species. All four are things you can check against your records from the day you prepared that batch, which is exactly why you keep records.

One more thing to watch for as colonisation finishes. A bag can look white on the outside while the centre is not yet fully colonised. If you move a bag to fruiting conditions too early, you get weak pinning, a poor first flush, and an opening for contaminants into a substrate that has not been fully claimed. When in doubt, give it a few more days. Mycelium that has finished colonising and is holding is far safer than mycelium rushed into fruiting.

Spawn is usually the most expensive input in a mushroom batch, so how much of it you use is a real business decision, not a technicality. The sources disagree, and the disagreement is instructive.

What the sources actually say:

• Botswana production guide: 5-10 percent spawn by weight of substrate, which is 50-100 g of spawn per kilogram of substrate. The same guide states a wider range of 2-10 percent depending on grower preference and budget.
• MushWorld handbook: 2 percent on a wet-weight basis.
• Kenyan golden-oyster trial: 5 percent.
• Nigerian Akure trial: reported in absolute terms, at 300 g of dry substrate per bag, rather than as a percentage in the detail retrieved.

That is a spread from 2 percent to 10 percent - a fivefold difference in the amount of your most expensive input. No source in this course's reference material settles it, and this course will not pretend otherwise by handing you one "correct" percentage it cannot defend.

What it can give you is the reasoning, which is more useful anyway. A higher spawn rate means more separate starting points for the mycelium inside the bag. More starting points means the mycelium has less distance to travel to claim the whole substrate, so colonisation finishes faster. And faster colonisation means a shorter window during which a contaminant could establish itself in unclaimed substrate. Remember what contamination actually is: a race between organisms, not a chemical problem. Spawn rate is you giving your organism a head start.

Against that, spawn costs money, and every extra percentage point is money out of the batch before you have sold anything.

So the trade-off is genuinely this: spawn cost against colonisation speed and contamination risk. If you are losing bags to green mould, raising the spawn rate is one of the levers worth trying. If your bags colonise cleanly and reliably at the lower end, you are probably paying for spawn you do not need and could trial dropping it. Change one thing at a time and record what happened.

Now the arithmetic you must be able to do before you place a spawn order, using only sourced physical quantities and no invented prices.

The Botswana guide recommends 2-3 kg of substrate per bag, and a spawn rate of 5-10 percent, or 50-100 g of spawn per kilogram of substrate. Put those together and a single bag needs between 100 g and 300 g of spawn, depending on which rate and which bag size you choose within those recommended ranges.

Work a real order. You plan 50 bags for a first trial cycle, at the lower 5 percent rate and the smaller 2 kg bag size.

1. Spawn per bag: 2 kg substrate multiplied by 50 g of spawn per kg equals 100 g of spawn per bag.
2. Spawn for the batch: 50 bags multiplied by 100 g equals 5,000 g, which is 5 kg of spawn.

Now run the same 50 bags at the top of the range - 3 kg bags at 10 percent - and the requirement becomes 300 g per bag, or 15 kg for the batch. Three times the spawn. That is the size of the decision you are making, and you can see it before you spend anything.

A note on bag size while you are choosing. The Botswana guide's 2-3 kg per bag and the Nigerian trial's 300 g of dry substrate per bag are both workable - the second is research scale. Bag size is a scale choice with a real trade-off: larger bags mean fewer bags to handle for each kilogram of substrate, which saves labour, but a contamination event inside one large bag destroys more substrate at once. A grower still learning their hygiene should lean toward smaller bags, because each failure costs less and each success is easier to attribute.

One last practical rule that matters more than the percentage you pick: mix the spawn evenly through the substrate in layers rather than dumping it at the top or bottom. Even distribution is what actually delivers the many starting points that the spawn rate is supposed to buy you. A 10 percent spawn rate all sitting in one place is a 10 percent rate you paid for and did not receive.

Colonisation is finished. The block is white and solid. Now you have to persuade the organism to stop feeding and start reproducing. That switch is called pinning, and it does not happen by itself just because time has passed.

The trigger is a combination of four things arriving together:

1. Full colonisation of the substrate. The mycelium will not usually fruit until it has claimed its food supply.
2. A drop in temperature relative to the spawn-run temperature. MushWorld gives the general principle that pins form roughly 10 degrees C below the mycelial growth temperature; the Botswana targets are 25-30 degrees C for spawn running and 20-26 degrees C for fruiting.
3. Exposure to light, after darkness during colonisation.
4. A large increase in fresh air, which brings carbon dioxide down sharply.

All four together say the same thing to the organism: the food here is used up and the outside world is available. That is when a fungus makes spores, and the mushroom is the structure it builds to release them.

Now the timings, and here is where more learners get confused than at any other point in the cycle. The sources report pinning from two completely different starting points, and if you mix them up you will wrongly conclude your crop is late.

Clock one, from full colonisation. MushWorld gives 4-5 days from full colonisation to visible pins. The Botswana guide then gives a further 3-4 days from pinhead to mature mushroom, with the mushroom roughly doubling in size daily during that window.

Clock two, from the spawning date. The Ethiopian trial measured days to first pinning from spawning: cotton seed hull 17 days, sawdust 29 days, wheat straw 32.66 days. The Kenyan trial did the same: maize cobs 19 days, sawdust 22 days, coconut fibre 23 days, against a 28-day control substrate. The Nigerian trial gives primordia at 18-25 days from spawning.

So when someone tells you "pins in five days", ask which clock. Five days from what? Your own records should always use clock two, the spawning date, because that is a date you know exactly, whereas "fully colonised" is a judgement call. Record both if you can: spawning date, colonisation-complete date, first-pin date.

Notice what the substrate does to this. In the Kenyan trial, maize cobs pinned at 19 days against 28 days for the control - nine days earlier. If you are a grower whose main problem is how long your money is tied up before any cash comes back, a substrate that pins faster is worth real money even if its final biological efficiency is only moderate. That is a genuine commercial reason to choose maize cobs in a maize-growing area.

Now the failure case, because it is common. The block is fully colonised and it will not pin. Work through four causes in this order:

• Still too warm. You carried spawn-run temperature over into what you are calling the fruiting stage. Without the temperature drop the trigger is incomplete.
• Not enough fresh air, so carbon dioxide is still high. Open vents. This is the most commonly under-done step because the room feels fine to a person while being stale to a fungus.
• Not enough light. The bags are still in the dark corner they colonised in, or still covered.
• Not actually fully colonised. It looks white on the outside and the centre is not finished.

Check them in that order, change one thing, and write down what you changed and on what date. If you change three things at once and pins appear, you have learned nothing you can repeat.

One last practical point about the pinning window. Once pins appear they are the most fragile thing in your growing house. A draught blowing straight across them dries them and they abort. A sharp drop in humidity does the same. Handle the room gently for those few days: mist the floor and walls rather than the pins, ventilate briefly and often rather than by throwing a door open, and do not move bags about. Then, over the next three to four days, the mushrooms roughly double in size each day and you are into harvest.

A colonised bag does not fruit once. After you harvest a flush, the mycelium recovers and fruits again, at a reduced yield each time, until the substrate is exhausted. Understanding that pattern is what lets you plan a sales calendar instead of being surprised by your own crop.

The basic pattern. MushWorld reports that most growers take three flushes from a single substrate batch. The same source gives a 7-10 day interval between flushes - that specific interval figure is given for straw mushroom cultivation rather than oyster mushroom, so treat it as a guide to the order of magnitude, not a promise for your crop.

How sharply does yield drop? MushWorld gives a worked example of 2 kg from the first flush and 0.5 kg from the second. Read the caveat carefully, because it matters: that example is for straw mushroom, Volvariella, not oyster mushroom, and it must not be quoted as an oyster-mushroom figure. It is included here only to show you how sharply yield typically falls away between flushes - roughly a quarter of the first flush in that particular example.

Now the honest gap, which is a real one for your cash flow. The Ethiopian and Nigerian oyster-mushroom trials both measured yield across two flushes rather than three, and neither broke out the first-flush against second-flush split in the detail retrieved. So the specific proportion of total biological efficiency contributed by the first flush alone, for African-grown oyster mushroom specifically, is not available in this course's source material. This course will not invent it. Knowing that roughly half, or two thirds, or whatever the true figure is, comes in the first flush would be genuinely valuable for planning your income across a cycle - and you can measure it yourself in one batch by weighing each flush separately, which is exactly what the capstone asks you to do.

What you can safely plan on, because the principle is well supported even where the number is not: each successive flush is smaller than the one before, until the substrate is exhausted. Plan the growing-room schedule and the sales calendar around a front-loaded, tapering harvest, not an even one.

How do you know a bag is finished? Three signals, in combination: the mushrooms get smaller flush by flush, the interval between flushes stretches out, and eventually the bag stops pinning at all. At that point the bag is occupying shelf space and contributing nothing, and shelf space is the thing you paid to build.

That brings you to the commercial decision this lesson exists for. Every extra flush you wait for is free mushrooms from substrate you already paid for, which argues for patience. But every day that bag sits on the shelf is a day a fresh, fully colonised bag could be fruiting in the same space, which argues for clearing it. The right answer depends on your throughput. If you are short of bags and have spare shelf space, take the extra flush. If your shelves are full and you have colonised bags waiting, clear the exhausted ones. Write down which choice you made and what the last flush actually weighed, and after a few cycles you will know your own cut-off point.

Between flushes, what should you actually do? Keep the conditions that made the first flush happen: fruiting temperature, high humidity, fresh air and light. Remove every stem stub and every piece of dead or aborted tissue from the bag surface promptly, because rotting mushroom tissue on a warm humid bag is a feeding station for exactly the bacteria and flies you spend the rest of this course avoiding. Then leave it alone and let the mycelium rebuild.

One scheduling point that ties back to the growing house. Because the harvest is front-loaded and tapering, a grower with a single room gets a lumpy income: a big week, a smaller week, a small week, then nothing while the next batch colonises. That is exactly the problem the Botswana guide's three-structure tier solves by staggering batches so there is a harvest most weeks. You do not need three buildings to start applying the idea, though. Spawning half your bags one week and half the next, in the same room, staggers your harvest at no capital cost at all - and a buyer who can rely on you weekly is worth more than one who cannot.

Biological efficiency, written BE and given as a percentage, is the single clearest number a grower has for whether their practice is improving. It is also the number most often calculated wrongly in the trade, and getting it wrong makes your own results look worse than they are and makes comparison with published figures meaningless.

The definition, exactly as used in the sourced literature: biological efficiency is the fresh weight of mushrooms harvested, expressed as a percentage of the dry weight of the substrate used to grow them. The Botswana production guide states the formula as:

BE percent equals fresh mushroom weight divided by the sum of dry substrate weight and dry spawn weight, all multiplied by 100.

Its worked example: a 3 kg bag yielding 1.8 kg of mushrooms gives BE of 60 percent. Check the arithmetic yourself - 1.8 divided by 3 is 0.6, times 100 is 60.

Now the mistake, and it is the whole reason this lesson exists. BE is computed against the dry weight of the substrate, not the wet, pasteurised, bagged weight. Substrate soaked to 65-70 percent moisture weighs far more wet than dry. If you divide your fresh mushroom yield by the wet weight instead, your BE will come out far too low and you will conclude you are a bad grower when you are simply doing the sum wrong.

So here is the habit that makes it possible: weigh your dry substrate before you wet it, and write that number down. That is the single most important record-keeping act in the whole production cycle, because that number cannot be recovered afterwards. Once the substrate is soaked, pasteurised and bagged, the information is gone.

One honesty note about the source. This course's reference could not fully verify from the Botswana guide's worked example whether the "3 kg" in it is dry or wet substrate weight. The definition line in the same source says dry substrate weight, and the definition is what you should follow. Where a worked example and a definition seem to conflict, use the definition - and record your own dry weight so the question never arises for your own figures.

Now, why do published BE figures sometimes exceed 100 percent? Because fresh mushrooms are 85-95 percent water, and BE compares a fresh weight against a dry weight. A substrate can and does produce a fresh mushroom weight greater than its own original dry weight. A BE of 148 percent is not an error and it does not mean matter was created from nothing - it means the mushrooms carry a great deal of water the dry substrate weight never counted.

Here are the sourced African figures, so you know what a real result looks like:

• Ethiopia: cotton seed hull 74.17 percent; wheat straw 35.88 percent; paper waste 34.22 percent; sawdust 9.73 percent.
• Nigeria: P. ostreatus on Terminalia ivorensis sawdust 48.83 percent; cotton 44.30 percent.
• Kenya: bean straw 106 percent; rice straw 92 percent; wheat straw 77 percent.
• Kenya, golden oyster on bean straw: 148 percent - the highest figure anywhere in this course's sources.

The Botswana guide separately frames greater than 60 percent BE as a target for farmers to maintain, with superior operations exceeding 75 percent. Treat that as one national guideline rather than a universal pass mark, especially since the bean-straw results above sit well beyond it.

One more thing worth walking through once, so you value your own results properly. BE compares fresh mushroom weight against dry substrate weight, and fresh mushroom is mostly water. Take the Botswana worked figure of 60 percent BE and the lower end of the water-content range, 85 percent water. Only about 15 percent of that fresh weight is dry matter. So the dry matter actually recovered is roughly 60 percent times 15 percent, or about 9 percent of the original dry substrate mass. That is not a criticism of BE - it is the correct standard metric used in every source here. It is a reminder that a BE of 50-100 percent is a genuinely strong biological conversion, not a modest one, and you should not undersell it by comparing it against numbers measured in different units.

Every grower loses batches. The difference between a grower who improves and one who does not is whether they can read the failure. This lesson gives you a diagnostic table built from the sourced material, and a method for using your own records to find the cause of a repeating problem.

First, the table. Symptom, then most likely causes.

Spawn run much slower than usual. Check substrate moisture; temperature too low; weak or old spawn; substrate nutrition poor for the species. Remember the sourced range is wide - 12 to 35 days across four sources - so "slower than usual" means slower than your own baseline, not slower than a book figure.

Green patches on the substrate surface during spawn run. This is Trichoderma, green mould, and it is almost always traceable to inadequate pasteurisation or sterilisation, contaminated spawn, or poor hygiene. There is no cure once it is established inside a bag. Remove the bag and dispose of it well away from the growing house, before it sporulates over the rest of your room.

Substrate fully colonised but will not pin. Still too warm, so the temperature drop never happened; not enough fresh air, so carbon dioxide is still high; not enough light; or not actually fully colonised despite looking white outside.

Pins form but abort and shrivel before maturing. Humidity dropped or swung sharply; a draught is blowing directly on young pins; the substrate surface dried out.

Long thin stems reaching upward, small caps. Carbon dioxide too high for the fruiting stage - not enough fresh air exchange.

Fruiting bodies discoloured, slimy, or caps showing water-soaked blotches. Bacterial blotch: caps stayed wet too long, or substrate moisture was below 62 percent at spawning.

Recurring contamination across many batches with the same pattern each time. This one is different from the others, and it is where records earn their keep. Trace back through your log to the spawn batch, the pasteurisation method, or a specific piece of equipment or hand practice common to the affected batches.

Now, two warnings about how to use that table.

First, it is a set of hypotheses, not diagnoses. No single source provided this table; it is a synthesis of separately sourced material assembled so you have one quick reference instead of scattered facts. Treat each row as something to check against your own records, not as an automatic answer. A symptom can have a cause the table does not list.

Second, and more important commercially: much of the pest and disease evidence behind these rows comes from US commercial mushroom literature, with essentially no African incidence data at all. This course's source material logs that plainly. The mechanisms are sound - a wet cap really does grow blotch bacteria, stale air really does produce legged mushrooms - but nobody has measured how common each of these problems actually is on African farms. Your own records are, genuinely, part of filling that gap for yourself.

Here is the method for a repeating problem, which is the hardest kind to solve. Take your last six batches. For each one, write down: spawn batch and supplier, substrate type and source, pasteurisation method and duration, spawning date, who handled it, which room it ran in, and what went wrong. Then look down the columns for what the failed batches share and the clean batches do not. If every failed batch used spawn from one delivery, you have your answer. If every failed batch was pasteurised on a day you were rushed, you have a different answer. This is why the record columns exist. Without them you are guessing, and you will usually guess the most expensive cause rather than the true one.

One discipline that makes all of this work: change one thing at a time between batches. If you switch substrate, raise your spawn rate and extend your pasteurisation in the same cycle, and the cycle works, you have three candidate explanations and no way to choose between them. You have bought a result without buying knowledge.

And one rule that is not about diagnosis at all but about your business: never sell a batch that shows contamination mixed in with clean product, even if only part of the harvest looks affected. Your customer cannot see the mould that was growing on the bag next door. A single reported illness or a visibly mouldy punnet damages a small grower's reputation far more than the value of the product you would have thrown away.