The substrate in which mushrooms are grown contains pasteurized materials that include chicken manure, horse manure, hay, straw, peat moss, gypsum, corn cobs and other organic materials. These materials are ground, homogenized and sterilized, which makes them an ideal fertilizer and soil conditioner for vegetable gardens.
The sterilization of the mushroom compost after the mushrooms have grown creates a soil amendment that is pure and rich in nutrients making it a nutritious product for growing plants.
Every time I find something I think I'm going to like I always read something that I don't like
Here's an article I found about mushroom compost
Commercial mushroom growers in the Willamette Valley grow tons of mushrooms in an elaborate mixture that gardeners love - mushroom compost. Often sold at landscape supply houses, mushroom compost can help amend garden soil, but should be used with caution, according to John Hart, soil scientist with the Oregon State University Extension Service. Mushroom compost is rich in soluble salts and other nutrients and can kill germinating seeds and harm salt-sensitive plants including rhododendrons and azaleas.
i find the same thing..there are always positives and negatives..i have access to seaweed..and i have read that it is good for the garden,however it is full of salt..some write ups say it is fine to use it...some say rinse the salt off before using it..i still havn't found a negative on it ,however if i keep looking i am sure i will find one..lol..confusing.