Monday, February 1, 2016

Growing Mushrooms in Aquaponics

Pioppino fruiting on a log in soil
When I first started experimenting with different ways to grow mushrooms, I found that one of the hardest parts was managing the moisture levels. If the mushrooms were in a pot with a drain, it was hard to get the water to soak in before it drained out. If the mushrooms were in a pot without a drain, the water stagnated in the bottom. Mushrooms lack the ability to perform evapotranspiration, or the ability to absorb water from the soil and evaporate it into the air like plants can do. Without this ability, the water stayed in the bottom of the pot indefinitely.

Adding plants to the pot helped quite a bit. Plants can perform the evapotranspiration for the mushrooms, keeping the water in the bottom of the pot fresh. However, if you want to maximize your mushroom harvest, you want as much of the "soil" to be wood chips as possible. That doesn't leave a lot of room for the plant. As mushrooms decompose wood chips, they have to grow into their food source. They need protein to grow, and protein contains lots of nitrogen. In an effort to be more competitive, they suck up all available nitrogen to speed their growth. This is very detrimental to plants. Most plants can't survive in a no-nitrogen environment, at least not for long. The mushrooms give the nitrogen back, but not until they are finished and their tissues decompose.

In my early experiments, I tried solving this problem by planting a mushroom log in a pot surrounded by woodchips. I gave the mushrooms a month or so to consume the wood chips and move into the log, then I added worms. The worms speeded the decomposition of the mushrooms and created a rich soil. The plants would flounder for 3 or 4 months, then turn green and healthy seemingly overnight as the soil reached a level where their needs were being met. But they didn't just come back to their normal levels, but rather an accelerated level of growth. The calla lily was particularly dramatic. While the wood chips were decomposing it always had 2-3 greenish yellow leaves and never got over about 6 inches tall. When the soil reached maturity, it turned bright green, grew to almost two feet tall, and packed on a dozen or so leaves. It was so vigorous I had to give the plant almost a gallon of water a week.

When I first created my aquaponics system, I buried several spent mushroom logs in my soil. I did it because I was just looking for enough filler material that I didn't have to buy any more soil than absolutely necessary. I built the bed in June in Phoenix, AZ, and between the fact that summertime temperatures can soar to 120 degrees F and the fact that none of the logs had fruited in over a year, I had no expectations that they would produce anything more. So imagine my surprise when the onset of fall dropped the temperatures and all of a sudden oyster and pioppino mushrooms started popping up all over the place.

Aquaponics provides a whole other level of not only hydration/oxygenation for the mushrooms, but support for the plants. An aquaponic bed is constantly flooded then drained with highly oxygenated water that is loaded with nitrogen and other nutrients from the fish. This keeps the oxygen and moisture levels ideal for the mushrooms and keeps the plants supplied with the nutrients they need. The mushrooms provide additional filtration for the water, but the plants get as much opportunity to get at it as the mushrooms do. The ready availability of nutrients means the plants can still grow vigorously despite the fact that they are growing in wood chips.

There are a couple of challenges with mushrooms in aquaponics. The first is the water quality. Wood is a formerly living thing and is loaded with all kinds of proteins and other compounds that are contained in the dried sap and tissues of the wood. The water flowing over them, as well as the decomposition going on, allows those chemicals to readily dissolve in the water. This will lead to a discoloration of the water that can initially be the color of strong coffee. Eventually, it will fade to the color of weak tea, but that can take some time. Also, for the first month or so after initial setup, the surface of the water can get foamy. The color in the water isn't bad for the fish, and may even be beneficial, as they absorb some of the natural compounds from the wood through their gills, but the foaming can be potentially harmful. This can be solved with some activated carbon thrown in the water or just reduced by periodically using the water to water plants outside the system until it goes away. I have never had a fish die from the water conditions that result from wood in the system. Well, technically I should say I don't KNOW of any. If they sank to the bottom, I'd never see them because the water was too dark. But usually they float, so I think I am okay saying that.

The other challenge is that aquaponics systems are full of worms. If you used wood chips, the worms will get in there and have a veritable smorgasbord. This will result in reduced yields for the mushrooms, but can be very beneficial to the plants.

There are a couple of ways to combat these problems. The first, and most obvious, is to grow the mushrooms on a series of mushroom logs buried in the media or soil of the aquaponics system. They can be oriented horizontally or vertically and function best if they are just a little bit, about 1/3, out of the media. This will keep them hydrated but give them access to fresh air. The solid block of the wood keeps the worms and other decomposing critters out and limits direct exposure of the wood to the water.

The second method is to start the mushroom block outside the system and transfer it in after it has fruited a few times. Obviously, this works best in an aquaponics setup with soil. It may fruit a few more times once introduced to the ideal conditions in the aquaponics setup, but the primary reason for this strategy is the significant benefit to the plants and living soil.

The third method, and one I intend to explore extensively over the next several years, is to carefully select the mushroom for the system. Some mushrooms prefer a vibrant soil ecosystem over sterile wood chips or a log. One such mushroom is the king stropharia mushroom. I grew king stropharia mushrooms in my aquaponics bed several years ago and got several pounds of mushrooms. King stropharia mushrooms won't produce mushrooms in a sterile ecosystem.

This is certainly an area where a whole lot more research is needed. I currently have on 2'x4' bed that works well as a test bed for mushroom/plant pairings, but considering the heat, I have to plant it in November and be done by late spring. Last year's experiment was king stropharia on palo verde wood chips and it was a resounding success. This year is king oyster mushrooms on palm fronds. We'll see how it does in the next month or so.