Growing Mushrooms

Ah, the fungus – beautiful, magical, mysterious, dangerous, and, most of all, misunderstood.  To most people, a fungus is a mushroom, but really the kingdom of Fungi includes yeast, molds, and a variety of other lesser-known fungi as well as the famous mushrooms.  Even the mushrooms themselves are only the tip of the iceberg of what they really are.  A mushroom is to a fungus as a flower is to a plant – simply a reproductive structure.  Just as the flower on a plant is supported by the roots and stems and leaves that make up the body of the plant, the mushroom that we see growing above ground is supported by the "body" of the fungus underground, a vast network of mycelium, or branching, thread-like hyphae that absorb nutrients from the environment.

Cool fungus on a tree in western Oregon

Fungi are decomposers who get their nutrition from breaking down dead and decaying animals, plants, and organic matter.  In this, their need for nutrition from outside themselves, they are more like animals than plants, and DNA comparisons have revealed that, indeed, fungi are more closely related to animals (yes, that includes humans) than they are to plants.  Needless to say that, after centuries of not seeing most fungi and viewing mushrooms as non-green plants, we are only beginning to understand how they operate.  In particular, figuring out how and when and under what conditions fungi reproduce has proven to be challenging for many species.  Until recently, an entire phylum, the Fungi Imperfecti, was reserved for those fungi who never appeared to reproduce sexually.  We don't know if or how they reproduce so we call them imperfect – talk about projection.

Yet not all fungi have proven to be so mysterious or difficult, and one species in particular, Agaricus bisporus, by virtue of its easy-to-initiate mushroom formation and reliable productivity, has become the mushroom that Americans grow, and buy, and eat, the most.  Agaricus bisporus, a native mushroom that can be found growing wild in parts of California, often in association with Monterrey Cypress trees, now accounts for 90% of mushroom production in the US.  There are two common strains of Agaricus bisporus – a white strain known as the button mushroom and a brown strain called the crimini mushroom (or baby 'bella) when harvested small, with closed caps, or the portabella mushroom when it is allowed to mature and harvested once the cap begins to open.

A few years ago, recognizing that I was a mushroom lover with grow-it-yourself tendencies, my mom sent me a button-mushroom-growing kit for Christmas.  The coldest months of the year turned out to be the best months of the year to grow mushrooms in central Texas, and I successfully harvested many mushrooms.  I also discovered that, just as a store-bought tomato can't match the flavor of a homegrown heirloom tomato, the ubiquitous button mushroom of the grocery store lacks the flavor and texture of a homegrown, freshly-picked mushroom of the same, humble variety.  Eaten raw in salads, fresh button mushrooms are sweet and juicy, with a texture just this side of crunchy.  Cooked in olive oil or butter, homegrown button mushrooms have the texture and meatiness of portabellas and are just as good with pesto.  Since that first year, the mushroom kit became something of a yearly tradition.

Homegrown mushroom pizza

This year, I received my mushroom-growing kit (from Pulpit Rock Mushrooms in southeastern Pennsylvania, the epicenter of US mushroom production) in mid December.  Inside the box was a large bag of compost with Agaricus bisporus mycelium growing throughout.  Agaricus bisporus is a secondary decomposer, meaning that it lives on compost that has already been broken down by bacteria and other fungi.  The compost in my mushroom kit was made from horse manure, with small amounts of nitrogen, gypsum, and water added.  The manure was composted for three weeks then spent a week in a high-temperature (140˚ F) room for sterilization.  Following sterilization, the compost was inoculated with mycelium from a white strain of the Agaricus bisporus mushroom, which was allowed to grow throughout the compost.

Also included in the mushroom kit were instructions for growing mushrooms and a small bag of peat moss.  Per the instructions, I poured the peat moss into a large bowl, added four cups of filtered water, and mixed until the peat moss was uniformly moist.  I spread the moistened peat moss over the surface of the compost.  This step, of adding a surface layer of peat moss to the compost, is called "casing" and is what stimulates mushroom production.  Throughout mushroom production, the casing layer, which must be misted regularly, will also provide necessary moisture to mushroom mycelium.  After casing, I carefully re-closed the box and stored it in a cool closet for about 15 days.

In late December, I retrieved the mushroom box from the closet and opened it to check its progress.  White, strand-like, mold-like mycelium had grown throughout the casing layer, so it was time to set the box up for mushroom production.  I placed the box on an old Chronicle (it felt appropriate to use the "12th & Nowhere" edition) in an out-of-the-way spot that receives indirect, southern light.  I folded the plastic flaps of the compost bag over the box ends, which effectively held the flaps of the box upright.  I thoroughly misted the top layer of peat moss.

Ready for mushroom production (December 28)

At this point, mushroom production is stimulated by three things: temperature, sufficient moisture, and sufficient air exchange.  The ideal temperature range for button mushrooms is 55˚ to 65˚ F, but luckily button mushrooms are among the least-fussy of the fungus when it comes to making mushrooms.  In my experience, button mushrooms will produce in my warm, central Texas house in the winter months, when the household temperatures are in the 65˚ to 75˚ F range, but tend to give up once the sun-heated days of spring regularly warm the house over 80˚ F.

The other two requirements for mushroom production, moisture and fresh air, are in tension with each other.  The best way to maintain humidity above the compost and moisture in the casing layer is to cover the whole mushroom-kit box, which prevents water from escaping.  The problem is that covering the box also stops air flow, which causes the carbon dioxide levels in the air above the mushroom compost to increase, which then inhibits mushroom formation.  So the mushroom grower has to find the best compromise between moisture and air flow, and for every species that best balance is different.  Again, luckily, button mushrooms are forgiving relative to other mushrooms, but they will fail to produce mushrooms if the casing gets dry or air flow is too limited.

I have found that the best compromise for button mushrooms is to leave the box uncovered but to mist regularly, two or three times a day, to keep the surface of the casing moist.  Watering occasionally is not an option – the surface of the casing has to stay moist.  Over watering will damage the mushroom kit as well, but can be prevented by misting the casing layer rather than pouring water into the kit as if it were a plant.  I use a clean (absolutely no chemicals in it ever because the fungus are sensitive) spray bottle with a non-drippy fine mist setting, filled with filtered or spring water, to mist the kit a few times a day.  This method requires regular attention to the mushroom kit, but each misting takes only a few seconds and gives me a chance to check on the mushrooms.

That said, I tried doing things a bit differently this year because the instructions that came with my kit told me to cover the box with cardboard and to occasionally mist the surface with water.  Being a good direction follower, I covered the box, even though I had not done so with kits in the past.  At first, mushroom production seemed to get going as usual but only one, albeit large, mushroom grew in the corner of the box, where the cardboard cover didn't quite overlap with the box flaps, while the other mushrooms that had begun to form as "pins" turned brown and failed to mature.

First mushroom (January 17)

After the first, big mushroom, all was quiet in the casing layer.  No more pins, or bright-white knots of mycelium that develop into mushrooms, formed in the next few days.  I suspected that the cardboard cover over the mushroom kit was the problem, either because my few airings-out a day were not generating enough air flow, or because the cover was blocking the indirect, natural light of the nearby window.  (Though mushrooms will produce in darkness, indirect sunlight is helpful.)  So I uncovered the box and went back to the tried-and-true method of misting a few times a day.  After a few days without the cover, new, bright-white pins formed and began growing into large mushrooms.

Second harvest (January 30)

The first week of February brought four days of freezing temperatures, and, even with the heat on 24/7 that week, out-of-the-way corners of the house dropped into the mid sixties as the cold wind blew through the fifties-built, insulation-free framing of this house.  While the freezing temperatures outside were life-threatening for the garden, the cooler temperatures inside the house initiated a new flush in the mushroom kit.  The flush began in the "pinning" stage, as bright-white balls appeared in the casing layer.

The third flush "pinning" (February 3)

Each "flush," or group of mushrooms produced at one time, varies.  Some flushes include only one or two mushrooms, which are often quite large.  Other flushes produce several mid-sized mushrooms or many small-sized mushrooms.  The third flush produced by my kit this year included many, smaller mushrooms.

The third flush ready to harvest (February 10)

Thanks to a cooler-than-usual February in central Texas, my mushroom kit continued to be productive.  As soon as I harvested the third flush, pins for a fourth flush were already forming.  Today I harvested the fourth batch of mushrooms and, once again, more are on the way.  I'm looking forward to a fifth harvest and a couple more weeks of mushroom pizzas, salads, and quesadillas.

The fourth harvest (February 19)