Over the past five years, I’ve gathered soil lab tests on various amendments, mixes, and composts, including both biological assays and elemental analyses. I'll be posting these numbers to this group as I continue to run tests, and I'd love to see anything you are experimenting with as well.
Most recently I ran an analysis of mushroom compost through two different labs (sending both the same material). This material (an unfinished compost) comes from a company that sells mushrooms to grocery stores around Texas, using spent material like mycelium and wood in thermophilic static piles.
I’d often heard that mushroom compost is high in salts, but I hadn’t seen data to back it up. I was curious since the chitin in mushrooms made them potentially appealing as a fungal influence in my vermicompost, but the results confirmed high salt levels and other elements of concern (mainly sulfur). Though a saturated paste test wasn’t done, the high salt content is still evident. This compost may be fine for top dressing, as salts can leach out with rain, but it’s not advisable for percentages in potting mixes or seed starting mixes, as an agronomist pointed out. While waiting for the labs, I decided to run a small test myself and mixed some of this compost with finished cow manure in a small vermicompost system. This also confirmed the material would not work for me. The worms were visibly distressed, staying on the surface and avoiding burrowing. Composts can vary greatly, so these materials could still work for you but I would just be cautious if you apply it to you worm bin. 