Place here sells it too, I'd also be interested, esp. as it's more expensive than the "regular" compost.

DH and I have talked about getting some. I think mushroom compost should be good, and if you go up there and get a pick up load ...well I haven't done the math, but it seemed reasonable when I last priced it.

Mushroom compost is highly variable and how helpful it is will depend a great deal on what sort of soil you already have. Spent mushroom substrate, aka fresh mushroom compost, is made by each mushroom grower's own formula, so its quality can var, and by the time they are selling the compost to the gardener, they've already used it and depleted some of the nutrients in it. It also tends to be alkaline here in this state and often high in phosphorus. So, if your soil already is high in phosphorus, it might not work well for you. One complaint about it in the past is that it tends to be high in soluble salts, which isn't good if you have native soil that is naturally high in salts, like I do. It usually is a blend of ingredients, including (in Oklahoma), wheat straw, composted cottonseed meal, poultry litter, and maybe some other ingredients like gypsum. Some companies use soybean meal instead of or in addition to composted cottonseed meal.

Keep in mind that the mushroom compost is added to soil as a soil conditioner, not as a fertilizer since the mushrooms have already sucked up all the nutrients from the soil that they needed. You'll still need to add other amendments to your soil to get the nutrients your plants need. Most places, like J&M in Miami, OK, pasteurize their spent mushroom substrate before they sell it. That's probably a good thing.

I have used mushroom compost in a limited amount and liked the way it helped turn red clay into fluffy soil, but I don't use it any more and haven't used it in quite a few years now. As long as you add it to soil and don't add too much, I think you'll be happy with the results. I wouldn't use it for sprouting seeds. For some reason, seed germination often is poor if someone is trying to use pure mushroom compost as a seed-starting mix. If you go to pick up a truck load, please understand it usually comes out of the mushroom growing facilities wet and heavy so be prepared for that.

That was a very thorough and accurate response!! Okiedawn knows her stuff. And the comments are not just specific to OK - the attributes described are common to mushroom compost from pretty much any source.

Among other horticultural topics, I teach classes on soils, composts, fertilizers and amendments so it is a subject I am pretty familiar with and the thread subject line just caught my eye.

I use it all of the time and I have great soil, but I also ad chicken manure every winter as well, and tons of leaves. It is fresh when you get it and is very heavy. The first years I got it, it smelled like horse manure, but in the last few years it seems to have more poultry manure which isn't surprising with all of the commercial chicken houses around. One year that gave us a copy of the ingredients, so I guess it is available. I think it is good stuff. I would never start seeds in it however.