Propagating Mushrooms

Mushrooms are hardy organisms. The mycelium of a mushroom producing fungus is capable of living for hundreds of years, perhaps more. For example, there is a patch of Armillaria mushrooms in Oregon that is believed to be over 2,000 years old. However, most of these magnificent organisms rarely live more than a few years. This is because of fungus’s way of eating. It grows into its food source and lives there until the food is gone. Unless it has another nearby source of food to grow into, it will starve to death and die. The art of propagating mushrooms is primarily the art of transferring the mycelium from one food source to another to keep it going as long as possible.

There are several ways to propagate mushrooms. In commercial production, they work under sterile conditions and take a sample of mycelium, either from the center of a fresh mushroom or a stored mycelium, and grow it onto agar in a petri dish. Then they transfer it onto sterilized rye grains (sometimes more than once) and then transfer it to pasteurized straw or wood chips for the final production of mushrooms*. However, in most people’s homes, mine included, sterile conditions are a bit hard to come by. So I will talk a bit about methods you can use that don’t require sterile conditions.

What we are going to be making is called spawn. Spawn is a growing medium for mushrooms that is used to expand a sample taken from living mycelium in preparation for making something larger for producing mushrooms. There are many kinds of mushroom spawn, and selection of such depends on what you have on hand and what you are hoping to transfer mushrooms onto. For example, mushrooms that are going to be transferred onto a log might be cultivated in a different form than mushrooms that are going to be transferred to a wood chip bed. Below are some common kinds of mushroom spawn out there and a brief description. I will cover some of them in detail later in individual posts.

Plug spawn – Plug spawn is made from wooden dowels that are grown through with mushrooms and then hammered into logs.

Coffee ground spawn – Coffee ground spawn takes advantage of the fact that coffee grounds are small, easily colonized and pre-sterilized.

Cardboard spawn – Cardboard spawn makes a nice surface to sandwich between two layers and makes an ideal growth medium for mushrooms.

Bunker spawn – A large mass of myceliated material covered in a protective cloth coating is good for helping mushrooms leap off in less-than-ideal conditions.

Wood chip spawn – Wood chips give an easy medium on which to grow and expand mushrooms.

*Note that this is how most gourmet mushrooms, such as oyster and shiitake, are grown. Button mushrooms have different requirements and are grown on composted, pasteurized steer manure.

A Strategy for Growing Mushrooms

Imagine, if you will, a huge table in the forest. On this table, Mother Nature has laid out every kind of food you can possibly imagine. Meats, fruits, and vegetables of all kinds are all laid out and waiting to be eaten. Plants make their own food, so they have no need to come to the table. Animals have the great advantage of mobility and are the first to arrive at the feast. The animals hit the easy to digest, high energy foods, like fruits and meats, first. But they also take most of the vegetables and just about everything that is readily digestible. By the time the animals have finished, all that is left is scraps. The bacteria and the molds come next. Actually, they were always there as they are always everywhere in nature. They have limited abilities of movement, but their real advantage is their ability to multiply rapidly. However, by the time they reach sufficient numbers, the table is all but clean. No matter, the bacteria move in and consume the scraps left by the animals.

The very last diner to the table is the fungi perfecti, the mushroom producing fungus. They come in blown by the wind or they grow to the table through the soil. Either way, it takes them a week or more to get to the table and amass any appreciable size where they can really take advantage of the food. By this time, though, even the scraps are gone. This doesn’t really bug the mushrooms, though. They just settle right in and eat the table.

This mental image is what drives my designs for mushroom habitats. When growing a plant, you want to create the optimum conditions for that plant to grow, thrive, and out-compete whatever competition it will have. The same thing goes for growing mushrooms, remembering that their principal competition will be bacteria and molds. To do that, you need to control some key environmental factors to give the mushrooms the competitive edge.

Temperature

Bacteria typically grow best in warm conditions. That is why your refrigerator is cold. It inhibits the growth of bacteria. The same goes for molds. Tropical mushrooms, like pink oyster and paddy straw mushrooms need warm conditions to grow properly as well. However, most temperate mushrooms are well adapted for cooler temperatures. In nature, they live on the cool forest floor. Many, especially the enoki mushroom (Flamulina velutipes) are so well adapted to the cold that they will continue to grow in any temperature short of actually frozen. It is a strategy that serves them well. Mushrooms that can continue to grow in cooler temperatures can continue to grow and survive when their principal competition has gone dormant. Growing your mushrooms in cooler conditions (though not actually in the fridge) can help them out-compete bacteria and molds.

Moisture

One of the advantages of being a multi-cellular organism is the ability to transport nutrients from where you have them to where you need them. Now fungus isn’t as good at this as us vascular animals, but it can transport water small distances. It can also survive through fairly dry conditions (though complete desiccation will probably kill it) and come back to life when water is again available. Keeping your mushroom just a little damp, but not overly wet, will allow the fungus to grow without giving the bacteria the upper hand.

Food Sources

This is the area where you can really stack the deck in favor of the mushrooms. Many of the best gourmet mushrooms are primary decomposers of wood. That means that they will move into a solid log and consume it. Raw, unprocessed wood is a complete food for mushrooms. Now you could probably get better and faster growth by adding all kinds of additives. Mushrooms like sugar as much as the next organism. However, the more other stuff you add to give it more energy, the more you open the door to other organisms to move in and compete. Keeping the meal as hard to digest as possible gives the mushroom the advantage.

Surface Area

Controlling the surface area of your food source is another way to cut down on contamination in your mushroom cultures. Consider a log vs. a pile of sawdust. The sawdust is much more accessible to the mycelium. The mycelium can grow through it in just a few days and then begin digestion in earnest. On the other hand, the bacteria and molds around can also do that. A fresh log, on the other hand, is a solid block of hard material. The mycelium uses a combination of digestion and hydrostatic pressure to push its way through, but doesn’t leave much room for others to slide in behind it. It may take 6 months for the mycelium to colonize the whole log, but provided it wasn’t contaminated to begin with, you have a good chance it won’t become so in that period of time.

So just consider the various factors that are within your control when you are setting up the growing conditions for your mushrooms. A little tweaking of the conditions could mean the difference between a successful culture and lots of yummy mushrooms and a contaminated failure that is only good for the compost bin.

Growing Mushrooms vs. Growing Plants

Someone once described war as “long periods of boredom punctuated by brief periods of terror.” Change “terror” in that sentence with “excitement” and you have a pretty good description of growing mushrooms. With a plant, the seed sprouts and then gets a little bigger every day until it reaches maturity. With a little careful observation and an eye for detail, you can see the daily difference. You get a little satisfaction every day.

Growing mushrooms is quite different. When you start a culture, say with a stem butt, it sits for a day or two. Then it gets a little fuzzy. After a few days of the fuzz getting a little longer, all of a sudden it starts growing rapidly. It covers the surface of the substrate in long strands at a rate of an inch or more a day under ideal conditions. Then, behind the leading edge, the webbing starts to fill out, claiming everything as its own. In just a few days, the surface is covered with a white blanket. Then it sinks in.

After the initial push, the white sort of goes away; it is like it dives down into the substrate to eat. At this point, nothing really happens for weeks to years at a time. If it is a log, it will take 6 months to a year or more before anything else happens. If it is something like sawdust spawn or coffee grounds, it will only take a month or so. During that period, it won’t change a bit. You can look at it all you want, but you won’t see any change.

Then, one day, something new appears. They are called primordia and they look like little pinheads on the surface. They show up overnight, sometimes by the dozens and start to grow. They expand in size and get taller. When they get about a quarter of an inch tall, they stop growing and dry up. I liken this step with testing the water. Maybe the first batch didn’t have the right mixture to survive in this environment, but in my experience, the first flush of primordia almost always abort. A day or maybe two later, a second batch will show up. This one has the right conditions. Pretty soon the primordia have grown into buttons and the buttons have grown into full grown mushrooms. The whole process, from primordia to full grown mushrooms usually takes about 5 days, sometimes less, occasionally more for large or woody mushrooms. It is very exciting. Sometimes you can come back and see noticeable growth after just a few hours. Talk about instant gratification! And when the process is done, you get to eat the results. You just can’t beat that.

A Compost Project

In addition to a trash dumpster and an oversized recycling bin, my neighborhood has a compost bin. It has two large bins that are big enough that one can be composting while the other handles waste from the entire neighborhood. It also has a central section with a roof that is used to store bales of straw that are to be mixed in with the kitchen waste to achieve the right mixture. It has slats on the front for easy extraction of finished compost and a sturdy wire mesh all the way around to keep the varmints out. All in all, it is a fantastic addition to the neighborhood. But it lacks one thing: maintenance. The neighbor who built it also takes care of it. The problem is that he lives elsewhere all summer, not arriving in town until mid-fall and leaving again mid-spring. That means that all summer, when the compost should be cooking like crazy, it never gets turned and rarely gets watered. In addition, the straw, which should get added when the compost gets smelly, gets added liberally with almost every addition of compost. So in addition to not getting enough oxygen or water, it has too much brown material. It seems to me that this is a problem I can fix. Since this is a blog about engineering with biology, we will tackle this as an engineering problem.

Problem Definition

The first step is to clearly define your problem. In this case, we will define it thusly: The compost bin only gets watered in the winter, has too much brown material and never gets turned.

Parameters

The next thing you look at are the parameters of your problem. Cost is nearly always one of the parameters. For example, those 14’ long giant worms from Australia might be just the thing for this problem (but probably not), but it wouldn’t be reasonable (or legal for that matter) to import a few of them. We need to spend little to no money and use local materials as much as possible. The second parameter has already been mentioned: we will be using biological organisms to solve this problem. The third parameter is a request from the person who built the bins: “I’d rather not modify them any more than I have to; I like them the way they are.” And I agree with him.

Options

The next thing we want to consider is our options. The usual composting organisms sound like a good place to start.

Thermophilic bacteria are the biggest composters out there. They work quickly and could turn that entire pile into black gold in about two months. There is a big problem though, they need a steady supply of oxygen (usually supplied by turning the pile), lots of moisture (only available during the winter), and warm temperatures (not available during the winter).

Redworms are the second biggest composters out there. They also work quickly and would turn that pile into black gold in about 2 or 3 months, if added in sufficient quantities. If worms are added to a dry pile, they will seek moisture deeper in the soil, even if it means leaving a huge source of food behind. They are also slow to eat brown material and they tend to go dormant in the winter, retreating to the bottom of the pile and slowing down their metabolism. Now the pile is in a sunny location, so it will probably not freeze solid during the winter and it probably will thaw all the way out most days, but it will still be too cold to keep worms active.

Mushrooms are another organism that can be used in compost bins, but isn’t used frequently. The problem with mushrooms in compost is that they don’t like to be turned frequently, they prefer a mixture that is heavier on the brown material and lighter on the green material, and they are damaged by high heat. See where I am going with this? Mushrooms will work slower than bacteria or worms, but will do an excellent job of breaking down the brown material. They also have limited ability to transport things like oxygen and can continue to grow a little deeper in the pile than the aerobic bacteria. In addition, they are typically better adapted to cool conditions and can continue to grow in just about anything above freezing. In fact, many mushrooms use winter as an opportunity to get a leg up on the competition, expanding their range and collecting nutrients while the bacteria are dormant.

Choosing a Specific Material

Engineering is all about specifics. Saying mushrooms will work is not good enough. You need to select a mushroom. As I mentioned, cost is certainly an issue, so I will work with the mushrooms I already have access to and see if any of those will be acceptable.

It turns out that I have access to four different kinds of mushrooms: 3 that I am growing and one that I harvested wild from nearby recently.

The first candidate is the elm oyster mushroom (Hypsizygus ulmarius) which I am cultivating on a couple of logs. It might be a suitable mushroom, but neither log has fruited recently, so I have no access to stem butts to make spawn.

The second candidate is the black poplar mushroom (Agrocybe aegerita), which I am also growing on logs and fruited recently. I am attempting to propagate this mushroom currently. However, this mushroom has proven difficult for me to grow. It is a primary decomposer, so it prefers raw wood (not so available in the compost bin) and it has had some difficulty with my dry Arizona climate. I don’t think this is a suitable candidate.

The third candidate is the pearl oyster mushroom (Pleurotus ostreatus). I also have this growing on logs, and it also fruited recently. The pearl oyster mushroom is a primary decomposer, but it is also an aggressive decomposer of all things that used to be plants. It grows well on paper, straw, cloth, wood chips, and much more, including compost. It would rapidly decompose much of the compost, but wouldn’t break it down very far. It would also die out when it ran out of nutrients.

The fourth candidate is the shaggy mane mushroom (Coprinus comatus) I recently found a fresh wild fruiting of this mushroom and harvested both dried mushrooms (they dry quickly in our dry air) and stem butts, which I am currently trying to grow on cardboard. Shaggy manes are tertiary decomposers, meaning they live in dirt. They are also great restorers of disturbed land. They are adapted to decompose anything from sawdust and straw to manure and yes, they do well in compost. They will probably work more slowly on the compost than the oyster mushrooms, but they have the added benefit that they are native to this area. They are also a great addition to garden soil and would get added to the soil with the compost.

At this point, I am trying to decide between the oyster mushrooms and the shaggy mane mushrooms. I think that a sequencing of both mushrooms would probably be best in the long run, with oyster mushrooms added first, followed by shaggy manes a month or two later.. Also, adding worms in the spring would help the compost finish quickly, especially if the mushrooms have pre-digested much of the compost.

Over the next month, I will be propagating and expanding the mushrooms I have before putting them in the compost bin. I will be posting several articles on the different propagation methods I use for the mushrooms. I will also keep you all up to date on further details of my compost remediation project. Also, sometime in January I will be teaching an informal class on how to propagate mushrooms, using the mushrooms I have, so if you live in the Prescott, Arizona area and are interested, let me know.

Best Garden Blogs

For those of you who haven't heard of it, there is a site called Best Garden Blogs that collects and links to the Best Gardening Blogs on the internet. I highly recommend you check it out as they have found some really great blogs. I am also happy to announce that they consider my blog worth including in their list.