All of our grow kits and substrates are made from bio materials and natural sources, your spent mushroom block will make extremely rich compost if added to your compost heap.Sometimes you will even get more mushrooms growing from your compost heap! Remove the bag and dispose of it in general waste. Unfortunately the biodegradable mushroom bags just aren’t up to standard yet, as they degrade into millions of tiny micro plastic fragments, for this reason we do not use the biodegradable bags currently until they are developed further..