Recently, I came upon a method of soil-building called hugelkultur. The basic premise is that decaying wood harbors a great diversity of life. If you see a fallen log in the forest, it is covered with different organisms. The older the wood, the more life there is. So, according to hugelkultur, when building soil, you bury wood in the soil. The wood provides both shelter and food source for a wide variety of life. Over the course of several years, the wood will break down into a rich soil that is full of organic matter and many nutrients.
When a mushroom log is good and spent, the interior is spongy and soft. They are easily chopped up into smaller chunks with a large knife. When putting together a new pot full of soil, I like to put a layer of well-draining material on the bottom, like sand or rocks, and then a layer of roughly chopped spent mushroom logs on top of that. I mix it in well with some good compost and then make sure I have three to six inches of dirt on top of the wood. This gives new plants plenty of room to spread their roots without running into wood immediately. While a plant can push its roots through mostly rotted wood, it may have difficulty with some of the harder portions or if you use fresher wood.
Thus far, I have only found two difficulties with hugelkultur. The first is that rotting wood is low in nitrogen. This means that your soil will most likely be low in nitrogen, too, so other sources, such as blood meal, compost, and nitrogen-fixing plants are a good idea as your soil matures, especially if you are going to be growing plants that need lots of nitrogen, like fruits and vegetables.
The second problem is that wood is high in carbon, which mostly gets converted to carbon dioxide as it decomposes. This is good for your plants, providing a slow, steady supply right where they need it. However, that carbon all takes up space. This means that the level of your soil will slowly drop as time passes, sometimes by several inches. This is great for annual plants, as it gives you lots of room to add compost. However, it can be bad for perennials as they slowly get buried in the compost you have to add.
Overall, though, I really like it as a method for bulking up soil in a new bed or container. I especially recommend it for mushroom growers, like me, who have lots of spent logs laying around that they don’t want to throw away.