A bucket of oyster mushrooms on straw: step by step, from pasteurising to harvest

We have often named it in earlier pieces as the logical second step after a grow kit: a bucket of straw with spawn. Cheap, big harvest, and it teaches you how growing really works. But it is also the method where things most often go wrong, almost always at one of four moments. Here is the complete method, with those four moments marked.

What do you need?

• An 80 gram pouch of oyster mushroom spawn. For a 10 to 15 litre bucket one pouch is plenty; more spawn means faster colonisation and less risk of contamination.
• Straw, about two kilos dry. Wheat straw from a farmer, stables or pet shop, cut or chopped into pieces of five to ten centimetres.
• A clean 10 to 15 litre bucket with a lid, and a drill to make holes in it.
• A large pan, boiler or drum to pasteurise the straw in hot water, plus a thermometer.
• Clean hands, a clean workspace, and an afternoon.

Step 1: prepare the bucket

Drill holes of 8 to 10 millimetres in the side of the bucket, in a diamond pattern every ten to fifteen centimetres, and a few in the bottom for drainage. The mushrooms will come out through those holes later. Then clean the bucket with hot water and a splash of vinegar or alcohol, and let it dry.

Step 2: pasteurise the straw

Failure point 1. Straw is full of mould spores and bacteria that will beat your spawn if you do not knock them out first. Pasteurising does that without the straw needing to be sterile. Heat water to 65 to 75 degrees, no hotter, because boiling also destroys the useful micro-organisms that protect your oyster mushroom. Push the straw, in a net or pillowcase, under that water for an hour, keep the temperature between 65 and 75 degrees, then lift it out.

Step 3: drain until just right

Failure point 2. Straw that is too wet is the most common cause of a sour, stinking bucket. Let the straw drain and cool to hand-warm, at least an hour, then do the squeeze test: grab a handful and squeeze hard. A few drops may come out, not a trickle. If water runs out, drain longer. If nothing comes out, it is too dry and can take a splash of clean water.

Step 4: mix and fill

Failure point 3. Everything that touches the straw now must be clean. Wash your hands up to the elbows, work on a wiped-down counter, and keep pets and houseplants away. Break the spawn into pieces and mix it evenly through the cooled straw. Fill the bucket in layers, pressing each layer down firmly so no large air pockets remain, and make sure straw with spawn sits against every wall with holes. Lid on.

Step 5: colonise

Put the bucket somewhere around 18 to 22 degrees, out of the sun, where it can sit undisturbed for two to three weeks. No light needed yet. After a week you will see white mycelium appear through the holes, after two to three weeks the straw is white right through the holes. Smell it now and then: fresh and forest-like is good, sour or alcoholic means too wet or too warm, see the smell piece. A single green spot at a hole can be removed; green throughout the bucket is lost and traces back to step 2 or 3.

Step 6: fruit

Failure point 4. Once the bucket is white, it wants the opposite of what it had so far: cooler, brighter and much more humid. Move it to 12 to 18 degrees, daylight without sun, and mist the bucket and its surroundings two to three times a day. Leave the bucket where it colonised, warm and dark, and you get nothing or only long stems. Within one to two weeks pinheads push through the holes, and five to seven days later you harvest.

Step 7: harvest and repeat

Harvest the fans while the cap edges still curl slightly downward, by twisting them off at the base. A bucket this size easily gives half a kilo to a kilo in the first flush, then two smaller flushes two to three weeks apart. Keep misting in between. When the bucket is spent, light and dry, the straw goes into the garden as soil improver or under the wine cap.

The four moments once more

Pasteurise between 65 and 75 degrees. Drain until the squeeze test is right. Work clean when mixing. And move to cool and bright as soon as the bucket is white. Get those four right and you will not have a failed bucket, and if you miss one, you now know where it went wrong. The second bucket is always better than the first, and the third is routine.