Harnessing the Power of Living Soil

A king stropharia mushroom growing among the carrots
in my garden system.

Viewing the world as an engineer, as I do, I tend to look at revelations and discoveries from the viewpoint of how they can be utilized to help solve real problems. Living soil is no exception. As I mentioned in my last post, living soil is excellent at balancing the chemistry and managing nutrient loads. But what can this insight be used for? How can it be used to make our lives better? A couple of years ago, I decided to combine aquaponic system design with the power of living soil. The success of the system has been a little surprising to me, even with my high hopes. The soil has proven to be very adept at balancing an aquatic system as well as its own and doing a great job of processing and retaining nutrients for the plants. Allow me to share two stories of things I have observed my system doing:

Story 1

Garden System Version 1.0

When I first built my system, I used a small aquaponics system with hydroton (expanded clay pellets) media and a 55 gallon sump tank. This was outside in June in Phoenix, Arizona, and the temperature was hot. I had to add about ten to twenty gallons of water a day to keep the levels up. Unfortunately, as water is lost in the system, the minerals are conserved. Tap water in my area comes out of the tap with a pH of 8.0. After a few weeks of concentration, my water was hovering around a pH of 8.6. At that range, the fish aren’t happy and the plants lose their ability to absorb a number of nutrients. I kept adding various acids in an attempt to get the pH down, but the fish didn’t like that process either and it never stayed down for more than a few days before I was adding more.

Finally, I managed to scrape together enough money and time to build my large garden bed. It is 4 feet by 8 feet and I filled it with a mixture of coconut fiber, wood (mostly spent mushroom logs), perlite, and compost. Then I added a generous number of worms before planting it. Immediately the soil sprung to life and began doing what soil is supposed to do. Within a matter of days the water dropped to a pH of 7.0. Over the next several months of intense heat and intense water loss and mineral concentration, it balanced out and eventually reached equilibrium at a pH of 7.6. This is actually a pretty good level for both the fish and the plants and it held that pH for almost a year without any assistance. The living soil in the garden, with plenty to eat, did its job and balanced the chemistry of the whole system, water included.

Story 2

My poor, sickly basil

Last spring, as the plants grew, I started noticing a nutrient deficiency. While most of the plants were clearly suffering from it, it was obvious that certain plants, like squash and basil, had it the worst. As new leaves grew, they would come out white, completely devoid of the necessary chlorophyll. I looked up the nutrient deficiency on my charts, as each deficiency has its own symptoms, and discovered it was definitely an iron deficiency and possibly a magnesium deficiency on top of that. So I added some chelated iron to fix the iron issue and some Epsom salts to fix the magnesium problem. I added a tablespoon or so of each every 2-3 weeks. After about a month of treatment, the white leaves stopped appearing and the plants resumed vigorous growth.

I continued the treatments for a month or so after the plants recovered, just to make sure they were going to be okay, and then I stopped adding the supplements. Not long after that, the weather warmed up. I had some nearby plants that were in containers, but outside my closed system. Rather than try to remember to water them twice a day, I hooked up a side line. Every time my system watered itself, a drip line also watered the container plants from the fish tank. An added benefit of this was that it prevented the buildup of mineral salts in my tank water. However, it also meant that all those great dissolved nutrients in the water were also lost. Now, more than six months have passed and there have been no return of the symptoms of nutrient deficiency. Since the soil is all the same but the water is all different, that means that the living soil snatched up all the nutrients it could get while they were plentiful and have been feeding them to the plants as needed.

I really think that the utility of living soil is one that is worth exploring further and including in more and more projects.

Soil as a Living Organism

Sometimes, looking at something commonplace with new eyes, new perspective, and new insight can be one of the hardest things there is to do. And sometimes there is nothing more important to do. What can be more commonplace than soil? We walk over it every day. Yet to dismiss its importance, its power, is to miss a great deal. Sylvia Bernstein, in her book Aquaponic Gardening, printed a quote from Kobus Jooste from South Africa that attempted to strip down soil into its constituents, ending in the following conclusion: “UBERFACT: Soil is an anchoring medium to plants that may or may not, over time, release some of the stuff plants need to grow.” I nearly stopped reading the book at that line, but powered on for the other wisdom the book has to offer. Still, that sentence comes back to me often. Rarely have people been more wrong.

The first thing to realize when looking at soil with new eyes is that soil is a living thing. True, it is not a single organism, but rather a complex media filled with tens of thousands of different organisms. But the organisms work so well together that they can almost be treated as one organism.  So, when a biologist studies an organism, what are the first couple of things they look for? Two of the most important aspects in understanding an organism are what it eats, and what role it fills in the ecosystem.

First let’s tackle the food source for soil. Yes, soil needs to be fed. Like any other living organism, soil breathes air, drinks water, and consumes a food source. In the absence of any of those, the soil will fail and die. As for what soil eats, it is really simple. It eats whatever organic matter falls to the soil surface. From there, through a series of digestive processes of different organisms, the particles of decaying organic matter get broken down into smaller and smaller pieces, the larger organic molecules digested into smaller ones. Mass is lost as carbon from cellulose and lignin and a host of other molecules are slowly turned into carbon dioxide. But the process is so much more complex. The cellulose and lignin were locked in what used to be the body of a plant, a plant that had metabolic processes and scent and its own DNA. All of those complex molecules that created the things that made the plant alive came with their own chemical signature. As they break down, the carbon is lost to the air, as is some of the nitrogen. However, the phosphorus and potassium and calcium and iron stay behind. They get recombined and further broken down by that wonderful process of decomposition and soil creation. What they finally create is exactly what the plants need to take up and start all over again.

The pile of mostly decomposed plants in the background
was living white clover two months earlier. The heat of
summer killed them and the soil gobbled up the readily
available food source.

 As an engineer, understanding soil isn’t just enough. What does it DO? What can I use it for? In order to tackle that question, I need to answer the other question: what role does soil play in its ecosystem? You probably learned in grade school science class, as I did, that soil provides nutrition and structure for plants. While this is true, it is a tiny portion of what is really going on. Soil plays an incredibly important role in the ecosystem. To work that out, let’s look again at soil’s food source. It needs decaying plant matter to feed on. Where does it get decaying plant matter? Well, it first needs healthy plants to grow, so they can drop leaves and eventually die. What produces more decaying plant matter, a lush growth of plants, or a few spindly plants that are already dying? Anyone with a lush landscape in their yard can tell you the answer to that one. The more plants there are, the more waste they drop.

So now we know that the soil organisms have a vested interest in growing a lush stand of plants. How do they do this? Again, we will answer a question with a new question. What is the biggest problem facing the plants? Plants need sun, water, air, and a good source of all the minerals and micronutrients they need to grow. The first three are outside the control of the soil organisms, but the last is fully within their control. There are two primary sources for the nutrients the plants need: decaying plant and animal material and the minerals in the soil around them. The soil needs to be effective at releasing those nutrients from both sources and getting them to the plants.

That brings up the next problem. How does the soil retain the nutrients long enough for the plants to get them? Have you ever performed a soil test? You put soil in a jar with water and shake it really well, then test the water for nitrogen, phosphorus, and potassium. Why is that? Well, the shaking is because the soil is working really hard to hold onto those nutrients. You test the water and not the soil because those nutrients are soluble in water. The soil has to find a way to lock those nutrients in, and where they fail, filter them back out of the water before they are lost to the water cycle.

It turns out that soil is remarkably good at doing just that. The bacteria produce polysaccharide glues that hold soil particles together. Fungal strands also serve to bind soil particles together. Fungal networks are shaped like a tight net, and have proven to be very good at filtering water.

There is another function of soil that is often overlooked. There is an old gardening addage: If you want to raise the pH of your soil, add compost. If you want to lower the pH of your soil, add compost. Plants are only able to absorb nutrients within a certain pH range. The problem is, different compounds work best at different ranges. Since the organisms in the soil have a vested interest in getting those nutrients into the plants, they also want to make sure the plants can absorb the nutrients. So they also take on the task of balancing the soil chemistry.

Naturally, all this is a gross oversimplification, but it has to be. There have been volumes written on tiny portions of this process. There are whole fields of science that study nothing but soil chemistry and biology. But when you think of the problems you have, think of what soil needs to do and how a healthy, living soil can help you and your plants. Then go out and feed your soil.

Water Spinach

I like to fill every possible niche in my ecosystem. Whenever I see a hole, I start looking for the right organism to fill it. So when I started a garden with a big tank of water, I immediately started looking for plants that would grow in water. I started by pointedly ignoring watercress (blech!), then moved onto water chestnuts. I found some and grew them for a year and a half before I went to harvest them and found they had all rotted away. But I digress.

Really, the holy grail for me is edible greens that will grow through the summer here in Phoenix, AZ. I love greens and would prefer to eat a lot of them. The problem is, most greens, like spinach and all of the various lettuces, go immediately to seed as soon as it gets over 80 degrees. Kales tend to be bitter in the heat. Chard actually does pretty well, but I would like a little variety.

My search for edible plants to grow in the water led me to one that meets both goals. Water spinach is the American name for a semi-aquatic, vining plant native to southeast Asia. The scientific name is Ipomoea aquatica. Known as ong choy in China and kangkong (LOVE that one) in the Philippines, it has many names. It isn't actually related to spinach, though. Ipomoea is the family that also contains morning glory and sweet potatoes. 

Water spinach has hollow stems that allow the plant to float on top of the water. An aggressive grower, it will spread across the top of whatever water you give it, forming a dense mat. It then shoots a thick canopy of leaves up above the water and a dense mat of roots down into the water up to two feet deep. In ideal conditions, which seem to be over 100 degrees Fahrenheit, full sun, and lots of non-stagnant water filled with abundant nitrogen from fish, it grows at an amazing rate. I have seen individual vines grow over a foot a day. I have harvested three pounds of leaves, leaving the plant looking picked completely clean, only for it to look like nothing at all happened four days later. It is far and away my most productive plant and I probably eat an average of 1/2-1 pound off of it a week, mostly as the greens for my morning smoothie.

While the flavor tastes quite like spinach, it is a little stronger, somewhere between spinach and kale. The texture isn't crispy like spinach nor tough like kale, though. It is more tender, like lettuce. About the last foot of the vine can also be eaten as well. The older vines are tough and somewhat woody, but the tender new growth is quite tasty when lightly stir-fried. Nutritionally, I haven't been able to find too much information, but it seems to be very similar to spinach. 

One of my favorite parts is that it is also a favorite edible of my tilapia. Any leaves that dip down into the water are quickly nibbled off. They also eat the roots, having a particular fondness for them. I once caught a tilapia fingerling and brought it inside so I could watch it grow. On a whim, I pulled off some water spinach roots and brought them in. The fingerling rushed to the roots and took a bite, Then it swam around erratically in what I can only describe as a happy dance, then rushed back and took several more bites. I accidentally killed my water spinach last year about this time and started some new from seed this summer. The new plant is almost as big as the old one was, but it still doesn't have any noticeable roots. The fish in my tank keep them well trimmed. I figure it is only a matter of time before the plant develops enough of a mat that it will get ahead of the fish. In the meantime, it doesn't seem to be suffering at all. 

There are a couple of precautions I would give. First, in its native habitat, the hollow stems are often a host for an intestinal parasite. The parasite isn't native to the United States, but be careful where you get your shoots. Or just start from seed. It is also considered an invasive and has become a problem in parts of Florida and Louisiana. So be careful where you grow it. As for my system, I really think that it is both an incredible boon and a bit of a nuisance. It grows in my main tank, and as such, gets first crack at the available nitrogen. I suspect the rest of my plants just get the little bit that is left after the water spinach is done. Also, while the floating mat provides great shelter for baby fish and shade in the heat of the summer, it also blocks access to oxygen exchange, necessitating an air pump if you have more than a few fish. 

Overall, though, I highly recommend water spinach for any sort of aquaponics or similar system. It feeds the fish and gives a steady supply of fresh greens for you all summer long.

Creating a Circular Economy with Mushrooms

Palm fronds from my back yard

Modern life poses an increasing number of complex problems, necessitating our coming up with ever better solutions. We know that our typical linear economy, that of manufacture, consumption, and waste, cannot be a long term solution. It is wasteful and inefficient. Mushrooms provide one very simple service that, with a little thought and planning, becomes a very powerful tool. Mushrooms use our waste materials as inputs, giving food and, with a little extra work, soil as an output.

I recently went to a presentation on creating a circular economy, where a city official talked about difficulties with palm fronds in the waste stream. Most green waste gets chipped, shredded, and composted. Palm fronds pose a unique problem, though. They are very fibrous and tough to cut down to a size that can be composted. Since the area in question, Phoenix, Arizona, is subtropical, there are a lot of palm trees around, providing lots of palm fronds to the waste stream. During the presentation, the city official mentioned that they have requested proposals for finding new ways to dispose of the palm debris, without much response.

After the presentation I asked him if anybody had suggested growing mushrooms on the palm debris. No one had. I told him that the palm fronds have a density somewhere between straw and wood and aren't particularly aromatic. They should break down pretty well with the right mushroom. When I got home, I did a little research. Pink oyster mushrooms (Pleurotus djamor) are a tropical mushroom that grows best in warm climates. Like most mushrooms, the pink oyster mushroom has certain preferences on what sorts of organic matter it prefers to grow on. It prefers to grow on tropical woody debris like palm wood and palm debris. Also, being a hot weather mushroom, it grows fast in hot weather. I wasn't able to answer detailed questions, like how long will it take to break down the palm fronds, but I am currently working on an experiment growing pink oysters on some palm fronds from my own back yard.

The whole interaction was actually weird for me. Normally, when I mention that mushrooms might be used to solve a problem, get a LOT of eye-rolling. People hear the word "mushroom" and mentally add the word "psychedelic." I didn't get that in this crowd. The talk was about creating a circular economy. It was a very receptive crowd.

When looking to create a circular economy for most sorts of green waste, mushrooms are a natural fit. In natural systems, the inputs come in the form of good soil, fertilizer (sometimes the soil and the fertilizer are one and the same) and sunlight. Progressing through the system, the plant grows, produces whatever product is desired, then dies. The end result is slightly depleted soils and dead plant matter. In order to create this into a circular economy, all you have to do is find a way to turn the plant waste back into fertile soil. Compost is the simplest way to achieve this, but it is labor intensive and doesn't add any value other than closing the loop to improve the soil. Adding mushrooms to the process helps considerably. By adding the production of another saleable output, the whole process gets improved. It becomes more profitable to close that loop and provides incentive.

Mature garden bed with mushrooms growing between plants

The problem is, this is still short-sighted. There are many more opportunities here. It isn't as simple as "just grow mushrooms on the waste product." Mushroom growing as a business is very equipment intensive, labor intensive, and knowledge intensive. But it doesn't have to be. Just as seed production is a separate business that helps farmers, mushroom spawn production could be centralized. Mushroom production involves several levels of spawn production before the final inoculation to produce the flush of mushrooms. Most mushroom businesses today create their own spawn, but that doesn't have to be the norm. A business could be created that helps farmers set up an outbuilding on their properties for mushroom production. Rather than each farmer creating their own biology lab, they would just buy the final run of spawn and use it to inoculate their waste. That process is pretty simple and easily learned.

But what about yard waste? What about those palm fronds, not to mention the logs, leaves, and other yard debris? Again, a business could be built out of it. They could be local, community centric organizations that somehow collect yard waste and turn it into mushrooms. It could provide for community employment. Again, the spawn production could be done elsewhere and just sold or distributed as needed.

Garden bed pictured above, before planting

Let's look again at that circular economy. What if you could contract that circle a bit, and overlap functions? In my last post I mentioned a different way of gardening. It just so happens that this type of garden allows you to decompose organic matter WHILE growing plants in it. I will get to how all that works soon, but trust me, it can be done. I have been doing just that for a couple of years. Through the addition of mushrooms to the living ecosystem that you are recirculating water through, you can increase the production of the whole system. As the mushrooms decompose the plant matter, they produce quite a bit of carbon dioxide. Might as well put plants right there to gobble it up as a food source, right? As the mushrooms decompose the organic matter, they release nutrients. Might as well sink some plant roots in it to take advantage, right? Mushrooms also function as a really effective water filter. They will help catch even more of the nutrients you are cycling through the system in the water. All of a sudden that little community mushroom growing business is also pumping out fresh produce as well.

So what do we need to get all this going? First of all, we need research. I only know of two experiments that have been done that test plant-mushroom pairings. Certainly some mushrooms are going to be harmful to plants and others will be beneficial. We need to find out which is which. What about climate differences? Paul Stamets, who has done a lot of the mushroom growing research to date, lives in the Pacific Northwest. One of my favorite lines is when he calls king stropharia mushrooms a summer mushroom, preferring to fruit at temperatures up to 90 degrees. Where I live, that is a winter mushroom. But there are others, actual heat loving mushrooms, that would probably thrive here. Pink oysters (Pleurotus djamor), king oysters (Pleurotus eryngii), black poplars (Arocybe aegerita), milkies (Calocybe indica) and paddy straws (Volvariela volvacela) are all native to warmer regions and could do well in southern settings. We just need to work out how best to grow them.

There is one more thing, though. It isn't just the science we need to work on. We need to also work on the marketing side of things. If we all of a sudden start flooding the market with mushrooms, we need to create a market for them. We live in a society that has a lot of phobias around mushrooms. We need to teach people about the new kinds of mushrooms hitting the market. We need to teach them how to cook them. We need to teach them how healthy they are. Most of all, we need to rebrand mushrooms as the food that helps the environment.