Using Compost Tea in Hydroponics


July 11, 2016

Sometimes soilless growing benefits hugely from soil techniques. For example, using compost tea in hydroponics. Breaking the rules can sometimes alter everything from your plants’ perspective.

When people are first introduced to hydroponics, they marvel at the concept of roots growing in water and the “technology” involved. It seems like magic to produce yields ten – even twenty times larger per acre than those accomplished in soil.

Basic Needs

While these are certainly real and relevant ideas, the reality is that a plant is a plant. Even if it was growing on Mars, it would still require the same basic requirements provided by Mother Nature. The name of the growing game is how to deliver these most efficiently and effectively. This is best accomplished by considering what the plant wants, not what we want to get out of the plant. Think of it this way, it is one thing to allow a plant to grow, but it’s another entirely to allow your plants to thrive.

For instance, as is attested to by anyone who has used them, a basic hydroponic nutrient is sufficient to grow a plant successfully. In other words, it’s designed to provide everything the plant requires to grow, which amounts to anywhere from 15-17 elements, depending on who you ask.

Now, let’s ask ourselves a question. There are over 90 Earth-bound elements on the periodic table, so why would Mother Nature make an element not needed in the garden? Think about that. Does a human truly know what a plant wants?

Hydroponic vs. Organic

The fact is that using natural and “organic” products allow people to use a wider variety of elemental nutrition unconsciously without choosing to bring these materials to the table because they are diverse by Nature. This is the basis for the generally accepted concept that hydroponics delivers higher yields, but “organics” brings a higher quality. There is truth to this idea. But it is also true that you can get the best of both worlds.

To express these ideas fully, it helps to have a clear delineation of soil growing versus hydroponic growing. In the simplest terms, hydroponic gardening is an emphasis on growing the plant, while growing in soil is a focus on growing the soil, or more directly, growing microorganisms.

Microbes are beneficial to plants directly through making perfect plant food and helping them eat it, as well as indirectly by acting as a preventive measure towards root and foliar disease, and pest infestations.

Land vs. Water

It is an apt analogy to compare the living organisms that make up the soil food web to that of the ocean food web. Microscopic organism activity supports the entire ecosystem of the ocean, such as photosynthetic bacteria or plankton. In general terms, the big fish eats the small fish, and all survive by attaining biological balance. The strength of the system is in the diversity, and the magic is found, not in a single component, but in the symbiosis and synergy of the web of life.

The same is true in the soil. Microorganisms, or microbes, are the plankton of the soil food web. Up to 50% of the food plants make for themselves in photosynthesis is actually fed through its roots as an exudate to attract microbes. There is an intelligence to this system, and take note that this teamwork is generally absent from a conventional hydroponic system offering only 15-17 elements and water.

Thinking about these systems properly is very important. In fact, it is the very act of treating soil environments like hydroponic applications that cause so many of the issues we experience on our farms and in our residential landscapes. Artificial products do not feed microbes. And microbes make plant food, people don’t.

Living Compost Tea

Given this understanding, the trick is in how to get microbes and the natural processes of Nature to support the yield-enhancing benefits of hydroponic applications. One of the best ways to do this is by using living compost tea. Compost tea is the act of growing microbes using diverse food and mineral sources within aerated water. The result is microbiological reproduction, and the perfect plant food being created.

While many choose to maintain “cleanliness”, in all reality, considering the above arguments, the most important place to use compost tea is in a hydroponic system. For instance, budget fertilizers contain maybe 7-8 total elements, a hydroponic fertilizer maybe 17, but a good compost tea recipe contains over 90 elements. Not only are there more elements, but they are more available, and there are more forms of them. Nature makes isotopes or different forms of the same element. Never heard of it? Look it up.

Elements Work Together

So there’s the total number of elements, and the form potential of those elements, but let’s take it one step further. The different elements actually work together to produce superior results in the garden. That’s right. It’s accepted knowledge in good agronomy that, for example, you want manganese at ½ of iron, or that zinc is 1/10th of phosphorous for plants to have adequate access to these elements. In other words, certain elements unlock others in proper ratios.

The idea is not to figure all of this out, it is arguable if that is even possible. But one thing is for sure: if you don’t put all the players on the field, your team will not win as many games.

The diagram below (Mulder’s Chart) is not proof of anything. It was put together by many people through many anecdotal experiences. And it is only scratching the surface. But most of the important information cannot be measured directly. Such is life.

mulders chart

Regardless, it provides a window into the complexity and potential of balanced growing with natural potential and hopefully challenges the grower to think outside of the box of good enough. We need to start asking ourselves what we’re missing before all we are left with are empty genetically modified plants. But that’s another article.

Lots Of Potential

Even one step further, it is important to consider elemental diversity from a plant’s perspective, but it may even be more important to consider it from a microbe’s perspective.  Microbes create and use enzymes to do their work, and every element on the periodic table has an enzyme potential.

compost tea in hydroponics

It’s called a co-factor, meaning the specific element defines the enzyme and acts as a backbone, so to speak. So in a very real sense, without all elements in your garden, it’s like hiring microbes to build a house and giving them only half the tools.

Compost tea can and should be used in every garden. Water culture hydroponics is a technique most vulnerable to root disease because the roots are constantly submerged in the reservoir solution. The illustration to the left shows this. The fertilizer solution constantly aerates the roots from the bottom as they grow into the solution.

The organisms that cause common rooting diseases are always present in a hydroponic reservoir in the same way that mold grows when a room is humid. Again, it is weak plants and inferior conditions that allow them to express themselves.

Case Studies

This grower had some browning roots that were limp and looked disease prone (pic at left below). The roots were not yet rotten, but slime coated, and the plant growth was limping along.
compost tea in hydroponics

Once the severely damaged roots were removed, and compost tea was added to the reservoir, BOOM, the fresh new white roots are popping out like crazy. The picture to the right above shows the difference only 48 hours after adding compost tea to the reservoir.

Below is 72 hours after adding compost tea to the reservoir with images of two more plants that were in the same system. All of them have pearly white roots exploding from the root system. The above images are the middle plant below.

new root growth in 72 hours

Here is another side-by-side from a customer using compost tea in hydroponics. In the image to the left, you see rooting before adding compost tea. The image to the right shows the same plant 48 hours after adding it.

compost tea in hydroponics

Following is a side-by-side we did in-house in an ebb & flow hydroponic system. They were grown next to each other in separate systems.

compost tea in hydroponics

The plant on the left was the control and grown with a base hydroponic fertilizer and water. The plant on the right received 1 cup per gallon of compost tea with the same base hydroponic fertilizer. The results speak for themselves. Many already use hybrid approaches using “soilless” mixes containing peat moss or coir fiber. They cost less and are suitable for making custom mixes. They are also better for establishing healthy microbiological activity.

In Case You Are Wondering…

Don’t be concerned about killing microbes with artificial hydroponic nutrients. You’re not helping them, but microbes are extremely resilient, and, generally speaking, if you are not harming plants with the salt toxicity, you are not hurting the microbes.

Besides, microbes actually act as a clearing solution. Most hydroponic growers tell themselves that living compost tea solutions will “contaminate” or “gunk up” their systems with bio slime, and all sorts of other scary things – when, in fact, the opposite is true. Use compost tea at a 1:20 ratio on reservoir changes, and you will have the cleanest reservoir you’ve ever seen. Try it.

Just goes to show that sometimes life is not as it seems. Consider the perspective that the first thing that we should know is that we don’t. The humility in this approach is where real progress is made.

Happy growing.

Evan Folds from Progressive Farms and Microbe Makers is a font of growing knowledge. This article was originally published in Garden Culture Magazine, Issue 3, under the title, “Soil Techniques in Hydroponics”. All images used as illustrations here were submitted by the author and may be subject to copyright violations published anywhere else.

Last updated by Catherine Sherriffs on 07/07/2020.

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Evan Folds

President at Be Agriculture
Evan Folds is a regenerative agricultural consultant with a background across every facet of the farming and gardening spectrum. He has founded and operated many businesses over the years - including a retail hydroponics store he operated for over 14 years, a wholesale company that formulated beyond organic products and vortex-style compost tea brewers, an organic lawn care company, and a commercial organic wheatgrass growing operation.

He now works as a consultant in his new project Be Agriculture where he helps new and seasoned growers take their agronomy to the next level. What we think, we grow!
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