Monday, January 31, 2011

Cardboard Mushroom Spawn

One of the great things about growing mushrooms is that growing materials are often free. Sometimes they even save you from throwing things away. Using cardboard as mushroom spawn is one such example. Cardboard is made of raw, unbleached paper, which is a good growing material for mushrooms and the corrugations are held together with a glue that is also very digestible by mushrooms. The channels in corrugated cardboard give the mycelium an easy channel to run down and travel quickly.

Personally, I find that mushrooms produced on cardboard tend to be kind of anemic. The open structure, while ideal for travelling mycelium, isn’t really dense enough to produce lots of mushrooms. However, the sheet form that cardboard comes in makes for easy transfer from one medium to another. If you are making a wood chip mushroom bed, you just lay down a layer of wood chips, then cover it with your cardboard spawn and then add another layer of wood chips, for a total of about 6” thick. You can use cardboard spawn for making mushroom logs as well. You take a chainsaw and cut a wedge in the log, line it with your cardboard spawn and hammer the wedge back in. When making a mushroom block out of wood chips or coffee grounds, you can just tear up the cardboard and mix it in. It will spread from the cardboard.

Making cardboard spawn is really easy. The first thing to do is find a good source of cardboard. Something that has already been through the mail is fine, as long as it isn’t covered in grease or other such toxic or unidentifiable chemicals. Cardboard spawn is best grown rolled up, so a container that will fit a roll of cardboard, like a glass jar or a bucket, works nicely. Then cut the cardboard to fit your container.

The next step is to clean the cardboard to remove potential contaminants. The nice thing about cardboard is that it is a pretty hostile environment, so you don’t need to worry about too many contaminants unless it has bee sitting outside for a long time. The biggest thing you need to worry about is mold spores. You will need to get rid of those. There are two basic ways to do that. The first is with boiling water. Put your cardboard in its container and fill it with boiling water and put on a lid if it has one. Let it sit about an hour. That will kill almost all mold and bacteria. The problem is, it also dissolves the glues, destroying the structure of the cardboard.  Fortunately, there is a second method involving hydrogen peroxide.

As many mushrooms grow, they naturally want to claim territory that they occupy as their own. One major source of possible competitors is spores of other fungi. Most mushrooms produce various peroxidase compounds as they grow. These compounds destroy the spores without harming the mycelium. Hydrogen peroxide is a very similar compound to what the mycelium produces and has much the same effect. So I will put some hydrogen peroxide in a spray bottle (or just transfer the spray nozzle to the peroxide bottle) and spray the cardboard down. I don’t dilute or anything. The hydrogen peroxide will break down into water pretty quickly and won’t harm the mycelium in small amounts.

Once the cardboard is treated, you can just layer your previous spawn on top. Wood chips from a spent mushroom block is a good medium of transfer. I also find stem butts particularly effective for transfer onto cardboard. Either way, you lay it on top and then roll it up as tightly as you can. Then put it somewhere and keep it moist. It is ready to transfer when the entire surface is covered with white, cottony mycelium and it no longer smells like wet cardboard.

Oh, and when you are finished transferring it to its new home, consider setting aside one sheet of cardboard. You can roll it in a fresh sheet of cardboard to make all new cardboard spawn.


  1. Great post! I have recently started making cardboard spawn from stem butts. My question for you is: do you ever have problems caused by senescence? My thought is that if i continue to fruit, then make stem butt spawn from that, then fruit, then make stem butt spawn and so on then I will eventually start seeing problems due to senescence. An obvious solution is to always start stem butt spawn from wild stem butts but they are not always available.

  2. It is my understanding that senescence isn't really an issue. There is one Armillaria individual in Oregon that is thought to be about 2200 years old. Generally mushrooms are killed by their food source running out and their inability to move to a new source. Commercial mushroom production involves finding a particularly productive strain and then cloning it and putting it in cold storage and maintaining it under ideal conditions for years or even decades. When they need to start a new batch, they take a small sample and grow it out. They will keep the same individual fungus going for decades. I really think of the propagation process more as feeding your mushroom than as cloning your mushroom. I have found that the limiting transfer issue in my case is contamination. I will transfer with coffee grounds / cardboard / wood chips / logs as long as I can, until contamination becomes a problem. Then I will take a stem butt and start over fresh.

  3. Thanks for the information Edmund. Others have cited the Oregon Armillaria in similar discussions I've had. In Mycelium Running, which has inspired my cardboard spawn pursuits, Paul does not mention senescence and simply states that when dealing with mycelium one must "move it or lose it."

  4. I really like your blog. Some of the biological stuff is too complex for me to understand, but I'm prepared to learn.

  5. pskept - Yeah, I agree with the "move it or lose it" concept, though in my case I think of it as feeding the mycelium. It is just that you have to take the mycelium to the food, not the food to the mycelium.

  6. b-a-g - I just found your blog today and I like what I see so far. I still have more to read. It is good to see a fellow engineer taking up gardening.

  7. One more engineer here :)
    Lovely blog thank you for the efforts.
    My question is how do you keep the cardboard damp? Do you spray it every day or you just keep the jar closed opening once a day for aeration?
    I am trying different media for spawn now and I get contamination on my ray grain :( it was going so well... :( but black pin head contaminated it (i guess because I was spraying the jar with water every other day)
    So I wander now how to keep the moisture in the jar without spraying water after inoculation. Can I just keep the jar closed and aerate it once a day?

  8. I do actually keep the jar closed and just open once a day. Sometimes I open every few days. Mushrooms are well adapted to live in low oxygen environments. They certainly need SOME oxygen, but really only need large concentrations of it to fruit. It is also possible to get filter fabric of some sort and that would also work, but the holes need to be small enough to keep spores out.

  9. Nice! That was a super fast and very helpful replay.
    And one more question if you don't mind. What happens if i take some mycelium from a jar that is not well colonized( it has just started the colonization) and try to start a new jar with it. Do I have a chance or I need to wait until the jar is fully colonized first.
    I'm asking that because this is my first attempt to grow mushrooms and I bought the spawn plug kit from fungi perfecti and I had several plugs left from the logs and I decided to try some stuff with them.
    So I'm using 3 plugs per jar. But one of my jars is gone due to contamination as I said. I want to take a plug that just started to spread in saw dust and start a new jar on cardboard and grain. Do you think that the mycelium that had already spread in the sawdust will continue to grow if I remove the plug?

  10. Fili - I am assuming that the plug you want to remove is not from the contaminated jar. If you remove the plug too early, it might slow the growth a bit. If you take the whole jar that isn't colonized yet and use it to colonize another jar, it will be very slow to grow out and may not work. If, though, as you say, the mycelium is growing out into the jar and you are just removing the plug to put in another jar, it should work pretty well and the mycelium left behind should continue to grow. Also, with the contaminated jar, depending on how contaminated it got, you might be able to save it. If the desired fungus got a hold of more than 3/4 of the substrate, you might be able to get some fruit from it, and if it fruits away from the contamination, you might be able to save the stem butt and use that to expand. What kind of mushroom are you growing?

  11. Thanks again for the help. I'm growing pearl oyster(Pleurotus ostreatus), shiitake(Lentinula edodes) and lion's mane(Hericium erinaceus) on logs. But experimenting only with the pearl oyster(Pleurotus ostreatus) as far as I know it is the most invasive mushroom and it should be the easiest to grow. I don't have a pressure cooker and am trying to sterilize the jars and the media in a pot, steaming them for 90 minutes.
    I'll try the hydrogen peroxide method. Do you damp the cardboard first in normal water or you use the water from the decomposition of the hydrogen peroxide?
    I already tossed out in the compost the contaminated jar(rye grain). The black pinhead developed so fast... And I read somewhere you can't save the jar and that it is bad to inhale the spores of the mold and it is recommended not to open the jar inside because the spores will spread and there will be future contamination. So this one is gone :)
    I'll give two more days to my sawdust jar to establish better mycelium and I'll take one plug from there to use on the cardboard.
    The goal is to produce enough spawn to be able to transfer and grow mushrooms on coffee grinds and to have some left to experiment with other media.

  12. Yeah, P. ostreatus is REALLY easy to work with. I really only have two problems with it - it doesn't work in my mushroom/plant pairings because it keeps killing the plants, and I use nematodes to keep fungus gnats down in my other pots, but it doesn't work in the P. ostreatus pots because the fungus eats the nematodes. Otherwise, it is quite vigorous in its growth. It sounds like you did the right thing with the contaminated jar if it was that bad. Hydrogen peroxide is mostly water anyway, so I use that to moisten the cardboard. It is only a 3% solution. Good luck with your transfer. I have some cardboard spawn that is taking a while to really get started, but I have a log fruiting right now and I'll use the stem butt from that to reinvigorate. Love this stuff.

  13. So when the mycelium is covering the cardboard, do you just take the cardboard and put it in with some fresh wood chips? and from there it'll start fruiting into pins and eventually mature mushrooms?
    and is it safe to eat?

  14. Chris - yep that's pretty much it. As for safe to eat, that depends on where you got your chips and your ability to identify your mushrooms. That is one of the reasons I recommend to people that they fruit their kits before expanding them. Not only is it more efficient and gives the kits a boost, but it also gives you a chance to observe the mushrooms as they grow and help you accurately identify them later.

  15. If I am after the stem butt am I going to want to pull the mushroom off. I've read a couple of sites that say to pinch the mushroom off or cut it, I don't think they plan on my spawning new mushrooms.

  16. I have been experimenting with Rishi/chi ling mushrooms using this method. I have noticed that as long as your samples are fresh it doesn't mater what part of the mushroom you use, the mycelium will grow as long as it is kept moist and in a dark environment. In my experience placing the mushrooms in the fridge over night prior to layering results in more vigorous growth.

  17. A really nice post. Ever grow magic mushrooms. I used too. The equipment I have now is about 5 years old