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.

Coffee Ground Mushroom Spawn

There is a fine line between a medium that is used for mushroom spawn (that is, to transfer to another medium) and one that is used as a growing medium. Some, like cardboard, are more structurally suited to transfer and may not have enough nutrition to take the mycelium all the way to a bountiful flush of mushrooms. Others, like straw, which is messy and difficult to fully sterilize, are more suited to fruiting and less good for production of spawn. Coffee grounds is one that is good for both. The granular nature of the grounds makes for quick and easily colonization by the mycelium. The process of making coffee out of the grounds conveniently sterilizes the growth media, limiting the opportunities for contaminants. The woody nature of the seed pod of the coffee bean also provides good woody material as well as abundant nutrition for the mycelium. Another nice feature is that most coffee filters are made of paper, which is also readily digestible by mycelium.

The first trick is to find a suitable mushroom to grow on coffee grounds. I have had great luck with both Pleurotus ostreatus (pearl oyster mushrooms) and Hypsizygus ulmarius (elm oyster mushrooms). I am currently attempting it with Agrocybe aegerita (pioppino/black poplar mushrooms), but my stem butt was small and it hasn’t made much progress yet. I suspect that there are other mushrooms that would do well in this medium as well, but not being a coffee drinker, I don’t have too much opportunity to try out new combinations. Also, I prefer to start my coffee ground cultures with stem butts from fresh mushrooms. If you are a one-pot-a-day household, this method works really well.

The method for growing mushrooms on coffee grounds is really easy. Wait until your coffee grounds are cool enough that they are no longer steaming, but not quite cold and put one pot worth of grounds, including the filter, in a bag or jar. Nestle the stem butt (or a little sawdust spawn, or whatever spawn you are using) into the center of the coffee grounds. In about two days, the spawn will recover from the transfer and will have visible signs of growth, in the form of a white, fuzzy coating. From there, you can add more coffee grounds at the rate of about one pot a day. Again, the coffee grounds should still be warm, but not warm enough to burn your hand. You add coffee grounds as the mushroom grows. If you start to get too far ahead of the mushrooms, as evidenced by a lot of uncolonized grounds in your container, stop adding for a few days until the mycelium catches up. The mycelium should more or less colonize the grounds after they have been in there just a day or two. If it takes much more than that, contamination can become a problem.

Moisture is another issue. Often coffee grounds have residual liquid in them. Mycelium can’t really colonize substrate that is under water. If I am using a gallon Ziploc bag, I will just pour the liquid out as it accumulates. In a glass jar, however, the liquid can be used for another purpose. Glass jars have less air flow than a bag that can be fully opened. When the jar is full, you can get fresh air down to the mushrooms if there is a little liquid in the bottom by just turning it upside down. As the liquid travels through, the pores in the material will be filled with air, which naturally has to be drawn from other areas. Just open the jar to get a little fresh air in the top, then turn it over and let it sit a few hours. Then turn it over again. Just don't do this before the jar is full as it will disturb the mushroom too much.

Overall, the container should be opened once a day to give the growing mushrooms a source of air. Usually this is accomplished when you open it to add the coffee grounds for the day. You can also give the mushrooms air flow by using a canning jar and replacing the sealing portion of the lid with a coffee filter (unused) or a piece of fabric.

Just keep the jar in a cool, dry location while it is growing. Once the jar is full and the mycelium has fully colonized it, as evidenced by the fact that it is all cottony-white and no longer smells like coffee, it can be used as spawn to transfer to another medium or it can be just fruited. To fruit it, give it another week or so to grow, and then open up the jar. Put it out in the light, but don’t put it in direct sun. Put a plastic bag over it as a tent, but punch a few holes in it for air flow. Then spray it a couple of times a day. Personally, I know a lot of people like to try to force the process, but I like to let the mushroom tell me when it is time. When, in the process of your daily airings, you see primordia, tiny baby mushrooms that look like pinheads, you will know it is time to fruit the mushrooms. You should get two or maybe three good fruitings out of a jar and maybe more out of a bucket.

Once the medium is done fruiting, you can still use it as spawn to start another kit. You can mix it with more coffee grounds, or just compost it again and start with another stem butt.