Extending 'mushroom kits'

[Mark Rand]

Mushroom growing kits are decidedly on the expensive side. I'm not sure if they are actually economic compared with buying mushrooms when you need them. Is it simple to take the expiring compost/hyphae and add it to newly made up compost to keep things going? If so, what sort of compost does one use? Sawdust, cardboard, sterilised garden compost, manure or other?

[ameno]

Growing mushrooms isn't easy. And those mushroom kits are certainly not economical. They are very much a gimmick.

I grew mushrooms quite a bit a few years back (doing it all myself from scratch, not buying the kits), so I know a fair bit about it. I gave up because it was a lot of time-consuming work and fiddly work in a glove box, and because I developed an allergy to oyster mushroom spores.

Anyway, using the block of mycelium you get from one of these kits to inoculate a larger substrate is definitely possible, but there are three major problems with this.
One, mushrooms do poorly against competition. This means the new substrate needs to be pasteurised. Not sterilised, but pasteurised. If you sterilise it, then it will very quickly be colonised by airborne bacteria, and the fungus will be out-competed. But if you do nothing you will also find it colonised by bacteria and moulds you don't want.
Two, it must be hydrated to the correct level. Too wet, and it favours bacterial growth and goes putrid. Too dry, and the fungal mycelia will struggle to colonise it.
Three, the bulk substrate is primarily just a source of carbohydrates. But mushrooms also need nitrogen to grow. In the blocks you can buy, the source of protein is the grain that the mushroom mycelia were originally grown on. But this won't last them indefinitely. Sooner or later they will exhaust it. But adding nitrogen sources (like more grain, manures, coffee grounds, etc.) to the bulk substrate is very risky, as a higher nitrogen content brings with it a far higher chance of rapid colonisation by things you don't want. For this reason, high nitrogen substrates (like the grain used to initially grow the mycelia on) are usually used only in completely sterile conditions, which on a large scale is impossible to achieve at home.

If you still want to try, then which substrate you use will depend on the type of mushroom.
For button, chestnut or field mushrooms, you use manure mixed with chopped straw, usually amended with powdered limestone to adjust the pH. This is a difficult mixture to get right at home, and more difficult still to pasteurise it properly and get the moisture level right. I would suggest not bothering.
For shiitake, sawdust amended with extra nitrogen is used. Again, very difficult to get right at home, and usually needs growing in actual sterile conditions.
For the various types of oyster mushrooms, and also for lion's mane, usually you would use chopped straw, but you can also use shredded cardboard (it's not as good and is more difficult to get the moisture right, though).
You can pasteurise your straw either with hot water, keeping it at 70-80c (no higher) for 40 minutes. Or you can give it a high pH bath, with means soaking it in a cold water solution of calcium hydroxide (builders lime) for 12 hours. You should stuff all the straw into a clean pillowcase or mesh bag prior to pasteurising.
After pasteurisation, the straw needs to be hung up to drip somewhere so that the excess water runs out. Once it is no longer dripping (it may also need squeezing a bit) it is ready to use.
You then need a large-ish lidded clean container (a lidded bucket is good), into the sides of which you should drill several 1cm holes. It is from these holes that the mushrooms will grow at a later date (1cm is plenty large enough). About quarter fill the bucket with the pasteurised straw, then break up your original mycelium block into golf-ball sized pieces, and scatter a about a third of them on top of the straw. Then do another quarter of the straw, then more of the mycelium block. Then another quarter, then some more. Then the final quarter of the straw. Then lid the bucket, put it in a plastic bag, and leave somewhere warm.
After the straw is fully colonised (usually 2-3 weeks if things went well), removed from the bag and place the tub somewhere it gets plenty of air and a decent amount of natural light, but which is also humid. Humidity can be increased artificially by spraying the holes with clean water. If it's a temperate climate oyster mushroom (normal or blue), then you may also need to lower the temperature slightly. Putting it outside somewhere shady is a good option, but beware of slugs. After a while, mushrooms should start sprouting from the holes.
The tub can often be re-used once or twice more. After it finishes cropping, allow it to rest somewhere warm for about 2 weeks, then soak it for 12 hours in cold water, then repeat the above process for inducing fruiting. This will usually trigger a second (smaller) crop, and sometimes you can get a third the same way.

See, it's a lot of work.

[Snoop Puss]

Really useful thread, Mark. And thanks for such a lengthy reply, ameno.

I've been pondering growing mushrooms these last few days after really enjoying some king oyster mushrooms at an outrageous price. But no way can I provide the conditions you're talking about ameno. Saved me a lot of thankless effort!

Many thanks again.

[Mark Rand]

Thanks for the heads up. I had wondered about the economics of it all. I'll carry on letting the shops provide the mushrooms.