How To Recycle Your Spent Mycelium Cakes

Published :

How To Recycle Your Spent Mycelium Cakes

There is more life left in your old mycelium cakes than you might think. Find out what to do with your old substrates with MushMagic.


If you loathe tossing your spent mycelium cakes in the dumpster, there are a couple of ways to recycle them for more flushes of your favourite fungus. The following suggestions are to help you decide whether to dispose of them outright, or reuse them in some way.

It won’t matter if things go wrong, because you made prints from the largest and healthiest mushrooms of the first flush to use for propagation—ensuring that ideal genetics are preserved and passed onto the next batch.

Substrates become spent either because there are minimal spores left to sprout into mycelium, or the nutrients are exhausted and there isn’t enough left to feed mycelium growth, let alone to produce fruits.

It’s one of those tough questions; fresh spores from prints will be far more vigorous than the dregs left over from two or three flushes. However, there is something satisfyingly frugal about getting the most out of every cake.

There is still much to understand about fungi and what makes them do what they do. Conventional thinking says the remaining spores didn’t burst forth in the first place because they were the least viable of the bunch. Radical thinking says the mycelium knew it was going to run out of room and signalled the remaining spores to remain dormant.

These suggestions aren’t do or die, and generally speaking, it is up to you what you do. The best results are always obtained from fresh, young mycelium that grows vigorously. As the mycelium mat ages, it becomes less virile, more crowded, and has less available nutrients for the ensuing flushes—yet it is not entirely useless.


When reusing spent substrates, two primary issues need to be considered: the principle of competitive exclusion, and senescence. Older cakes have the advantage of having “their own immune system”. The mycelium is the dominant species in the substrate and totally rules that territory.

When smaller pieces of the cake are used as an inoculant, the mycelium loses this advantage and goes into battle once more with any contaminants present. The advantage it does have in this instance is that it is already mycelium, and can start spreading immediately, rather than going through the process of spore incubation when the mycelium is at its most vulnerable.

Senescence is the same reason people get old. When genes make repeated copies of themselves, small mistakes are made, which accumulate over time. It’s like taking a photocopy of a photocopy of a photocopy. Eventually, it is unrecognisable from the original. People get wrinkles and other signs of ageing. Mycelium suffers genetic decay, loses vigour, and starts to produce odd fruits.


Spent substrate as an inoculant for a fresh substrate gives the reused mycelium a nutrient boost. When preparing a new substrate, crumble and mix the old one in with it. Incubate and fruit again. The downside being, the flushes aren’t as exuberant as a first run with fresh spores. Also, the old cake has had more time to acquire pollutants or other organisms that can affect the grow.

When using older cakes to inoculate new substrates, it helps to change the type of grain being used. This prevents the mycelium from becoming dependent on a particular nutrient source and stagnating. It’s kind of like changing up workouts so muscles don’t get used to doing the same exercises every day.

The bigger the piece of recycled substrate, the better. The more mycelium already present gives it a tactical advantage in the competitive exclusion race. It can spread through the new cake substantially before spores from competing contaminants have even come to life.


Recycling spent substrate in with a new batch of substrate is said to produce higher-quality shrooms. They are broken up and mixed in with the new material prior to the sterilisation process, so there is no cross-contamination.

The hypothesis is that the recycled mycelium breaks down into the types of essential nutrients that new mycelium require, while also supplying the tryptamine precursors used for psilocybin production. Ensuing flushes are more vigorous, with some anecdotal evidence that the effects are stronger as well.


Reuse the cakes by casing them. The casing, like mulch for standard plants, will provide a moist and humid layer to encourage more mycelium growth. Depending on what type of casing is used, it can add nutrients as well as boost humidity. The flush may not be as robust as those previous, and some mutant-looking fruits can appear.


If you have a yard with some spots that remain well-shaded, crumble the spent cakes up, spread them about, and mulch them with straw and leaf litter. Think about what a forest floor looks like. With regular watering and leaving a few fruits to mature until they naturally release their spores, you can have a successful seasonal outdoor patch. It will be subject to the whims of nature, but will produce what it can in its new home. Mycelium thrives—it is its nature. You don’t get to be around for hundreds of millions of years without being adaptable!


Great as a soil amendment or for mulching, vermiculite, grain husks, and other organic compounds help soils retain water while increasing friability for good drainage. This is true for outdoor and indoor plants.

Crumbling them up and putting them in your houseplants over time may produce more fruits. They will observably grow slower and nowhere near as dense, as they are no longer in a pampered environment. But the more the merrier, right?


Keep in mind, there is fungi senescence. Mycelium mats cannot produce forever and will eventually give up. However, it is unclear where this point is for psilocybin mushroom-producing mycelium. Some growers report reusing their cakes at least eight times before encountering any problems, while others run out of steam after two reuses. It probably has something to do with cleanliness and contamination, or genetic decay from spores from disreputable sources.