I found a mushroom farm place that has compost which it gives out free to the community. Is mushroom compost good? Here's an excerpt from their website

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Often referred to as "spent mushroom substrate" (SMS), Mushroom Compost is the composted result of a rich growth medium for mushrooms. It is made from agricultural materials, such as straw, straw horse bedding, cottonseed meal, nut shells, and gypsum. Sphagnum peat moss adds to the organic nature of the substrate, providing a consistent, formulated and homogeneous product.

After the mushrooms are harvested, the Mushroom Compost is steam treated prior to removal to eliminate any pest, pathogens and weed seeds resulting in a PDA accepted fertilizer product. Mushroom compost has high water and nutrient holding capacity and exhibits no nitrogen draw down problems. As a fertilizer and organic soil amendment, Mushroom Compost supports plant growth in a variety of applications to the lawn and landscape and inhibits Artillery Fungus.

Our mushrooms are Pesticide FREE and USDA Certified Organic (by Where Food Comes From Organic Inc). However, our compost is not certified USDA Organic, but we use all organic materials for our mushroom growing; zero pesticides.

How would you plan to use it?
I thought I've read it can be a bit high in salts. That is said in the link below..

RHS article says it can be slightly alkaline
https://www.rhs.org.uk/soil-co...

Free?
They usually charge high dollar for that stuff.
I'd get all they would let me have.

My experience with mushroom compost is that it varies a lot.
some batches have a high carbon content, some batches give better manure content.

I'd probably experiment with it, and mostly just top-dress the soil with it.

I just top dress my fruit trees, flower plants twice a year, spring and fall. Right now I buy G&B Soil Building Conditioner every year to do that.

Here's the breakdowns of their mushroom compost

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Compost Composition
Compost ingredients used may include:
Straw
Straw horse bedding
Cottonseed meal
Peat moss
Pistachio shells or almond shells
Gypsum
May contain wood chips/sawdust

pH 6.62
bulk density 574.73 lbs./cubic yards

Relative Value of Compost to Commercial Fertilizers
Numbers are calculated from a wet volume basis.
1 ton MC (equivalent to 3.5 cubic yards)
Nitrogen = 22.27 lbs./ton
Phosphate = 13.29 lbs./ton
Potash = 24.70 lbs./ton
Approximate weight: 30-35 lbs per cubic foot. 810-945 lbs per cubic yard

It's more on the alkaline side, but other than that pretty comparable to normal green waste compost.

I'd try and track the origin if manure was used, since some herbicides just pass through herbivore guts and might affect your plants (stunted/dead)...
Other than that, worst case scenario: you have mushrooms growing amongst your roses.

I love mushroom compost, though most of the oddball mushrooms don't sprout except occasionally, still, the mycelium part of the mushrooms is exceptionally good for plant roots when they do grow. It is usually really rich if not aged, so use sparingly if you think it will burn the plants.

My dad gets a load every year for his garden and it always does phenomenally. I'd jump on that offer if I could.

swear by it. Yeah the first load they dump smells but I like that manure-ish odor. Everything does well even with a top dress.

Hi Andy. Wanted to bring this thread to the top of the pile.

I'm in SoCal too (10b) & just scored a huge free haul today. It came looking like fire starter logs which surprised me because I was expecting to have to shovel it into containers to drag to my pickup. Have you learned any new info since this posted?

I've read it's high in salt & shouldn't be used to start seeds so just mix in & top dress my established beds, I guess. At that price I'll figure it out. 😂

Anything you read may be subject to the location and type of mushrooms being grown - they have to get the chemical mixes right or they mess up the shrooms, chuckl. If it is composted, it is well mixed and diluted, I use it the same as the other bagged stuff I throw in my beds or on the ground, 50/50 or roughly same and haven't had any issues. Logged compost, wow, gotta go see who imagined that into existence ( maybe accommodating a commercial machine)