All guesses are appreciated!

Exactly! If your friend likes Las Vegas he is going to have a lot of fun - it is just a crap shot if it is generic. Wherever he got, if anyone can have any science-based specific opinion to your friend's soil fertility, it is the person who made the mushroom soil, which we commentors are assuming is spent mushroom substrate sold commercially as used soil byproduct of mushroom farms.

The opinions we can give are not science based since the range of the SMS can be a wonderful nutrient mix, aeration quality & pH, to a lousy one, and the residual fertilizers may be helpful or burn the plants. We have no way of knowing and my opinions is it is not quite a 50/50 bet and the house will usually win. Better to amend the soil, but with what? We honestly could not tell you if we would overdo an existing problem or correct a deficiency. So...soil analysis or soil specs from the vendor which something tells me, may not be available, or Las Vegas

But he is already planted out .... so his chips are on the table and the dealer has dealt. Let' see what's under the dealer's ace! I would not add much and observe the plants by the seat of my pants initially, correcting deficiencies or problems as them came up. I would water plenty to leach it with time and as soon as that had effect I would start on my normal fertilizer program, whether it were organic or miracle gro, etc. I would try to stay low on nitrogen initially.

That is why not many of us use spent mushroom soil - because it is an unknown and not usually formulated as a reliable potting mix.

Cheers

PC

Yeah I suppose it is possible if he is very lucky. But it definitely isn't recommended. No active soil bacteria, minimal nutrients and essentially no minerals, minimal root support, etc. Where does he think the plants will get the minerals and base nutrients they need to grow much less thrive?

If he had an actual soil test done rather than some home test kit the results would have told him its very likely a no-go. Sounds like one of the many "I read somewhere" ideas we often get asked why they didn't work AFTER it's done. ;-)

Tell him even organic gardening has guidelines to follow.

Dave

It's pretty much planting in compost. Some people do that. Not a good idea because, in addition to the lack of nutrients, it is so fluffy that roots don't offer stability to plants. It doesn't hold water as well as regular soil, either. So even planting in SMS and throwing fertilizer on is not a particularly good idea.

You may find this helpful: Plant nutrients and fresh mushroom compost.

From the article:

"For many years, mushroom compost was mislabeled
as “mushroom soil,” and the product was unfortunately treated like a soil. As a result,
Pennsylvania’s mushroom industry had to deal with the negative feedback of trying to explain
why their mushroom compost was not behaving like topsoil. Mushroom compost is not topsoil,
rather an excellent compost useful to improve soil health and plant growth."

An additional note: mushroom compost is usually steam treated. This means that, unlike regular compost, it's not going to contribute much in the way of soil flora.

In addition, I believe that salt is added to the medium that becomes spent mushroom substrate (SMS) to encourage growth of the proper variety of mushroom. That salinity is not good for most vegetables, though it does leach out eventually.

Given all our guesses matter little if he/she is not open to making changes if it isn't already too late, let him treat it as an educational experience, albeit a negative one.

Dave

It would be interesting to see what happens, but if things grow well, I'm inclined to believe they would have grown better if the stuff had been added as a soil amendment.