Shiitake SpawnJar™

Species: Lentinula edodes

Form: Colonised grain spawn, one quart jar

Typical spawn rate: Around 10 percent into bulk substrate (5 to 20 percent range)

Block colonisation: Around two to four months (shiitake is slow)

Fruiting temperature: Roughly 13 to 21C, humid, with fresh air

Fridge life: A month or two, often up to about four

For: Indoor sawdust or pellet blocks, not logs

A jar of living shiitake grain

The jar holds sterilised grain colonised by shiitake mycelium until the grain is bound into a solid white mass. Shiitake is a hardwood mushroom, so the grain is only a carrier to multiply the culture. The real fruiting work happens later, once you have moved it onto wood.

Healthy spawn looks evenly white and smells faintly of fresh mushroom or damp wood. Any green, grey, pink or black patches, or a sour or off smell, mean it has picked up a contaminant and should not be used. Check the jar before you open it.

Mixing spawn into substrate

The usual route is to inoculate a hardwood substrate, most often supplemented sawdust or hydrated hardwood pellet (a common recipe is around 80 to 85 percent sawdust to 15 to 20 percent wheat bran), hydrated to roughly 60 to 65 percent moisture. Work clean, ideally in front of a still air box or flow hood, since this is the point where contaminants get in.

1

Break up the grain

Shake or loosen the colonised jar so the grain separates into individual pieces. Each loose, mycelium covered grain becomes a new starting point in the substrate.

2

Mix through the substrate

Add the spawn to your sterilised, cooled substrate and mix until it is spread evenly. Spawn rates usually run from about 5 to 20 percent by weight, with 10 percent a sensible starting point. More spawn colonises faster and resists contamination better. Stretching it thinner is slower and riskier.

3

Colonise in the dark

Seal in a filtered grow bag or container and keep warm and dark. Shiitake is slow. A block usually takes around two to four months to colonise fully, then often turns brown and forms a firm leathery skin as it matures before it will fruit.

4

Fruit it

Once the block has browned over most of its surface, shiitake fruits in cooler, humid, fresh air conditions. Fruiting commonly runs in the region of 13 to 21C with high humidity and good fresh air exchange. Many growers trigger pinning with a cold shock, soaking the block in cold water or chilling it for 12 to 24 hours. Conditions vary by strain, so follow a shiitake guide for your block.

One quart of grain spawn goes a long way. As a rough guide, a few pounds of grain spawn can inoculate well over a hundred pounds of sterilised sawdust, so a single jar covers several home sized blocks.

Keeping the jar alive

If you are not using it straight away, keep the jar sealed in the fridge. Refrigerated grain spawn stays viable for a month or two, often up to about four months, but vigour drops over time, so fresher is better. Keep it sealed and cool until the moment you inoculate. Do not freeze it, as ice crystals damage the mycelium. Let a cold jar come closer to room temperature before mixing so you are not shocking it.

Not a grow kit, not for logs

This jar does not fruit on its own. There is no sawdust block, no bag and no fruiting tent in here. You supply the bulk substrate and the growing conditions.

Grain spawn is also not used for inoculating logs. Outdoor log growing uses sawdust spawn or plug spawn pressed or hammered into the wood. Use grain spawn for indoor sawdust or pellet blocks.