If you grow mushrooms for any amount of time, you are going to quickly find yourself with large heaps of spent substrate. This may lead you to wonder, “What do I do with my old mushroom substrate?”. The most common option for mushroom farmers is composting.
It can be mixed in with your existing compost pile. Or, you can build a compost pile simply by using a substrate, which will naturally decompose over time and turn into rich compost. If you get a garden, you can even mix used substrate directly into the soil. Some big commercial growers even recycle their mushroom substrates and sell them to home gardeners as compost. You can learn a few more ideas from a video we liked below:
If you are lucky, you might be able to snag some additional mushrooms flies off of your compost pile or your vegetable patch. Some species, such as oyster mushrooms, may even grow firmly and propagate, and you may end up with a few free mushrooms growing in your garden from year to year. Some of your spent substrates can even be used to inoculate a fresh batch of substrate.
This way, you do not need to purchase fungus starter cultures from vendors, and can have a really self-sufficient operation. This type of low-tech mushroom farm may still result in a somewhat higher incidence of contamination. If you are a grower with lots of space, it is easier to handle disposing of used substrates yourself. But what about those growing mushrooms in cities.
A lot of cities now have free composting programs. You can probably get your used bedding into a compost bin, which gets empty every week. Or, you may have to take your used substrate to the municipal landfill, which handles yard waste, compost, and other recyclables, and take it there yourself.
If your city does not offer any ways for your substrate to be recycled, you may be able to contact a neighboring farmer. They might be willing to add your used substrate to their compost piles, and they’ll let you toss it in for free. There has even been research into using mushroom substrates as a component of animal and livestock feed mixes.