Using Compost Tea in Hydroponics


July 11, 2016

Breaking the rules: sometimes soilless growing benefits hugely from soil techniques. Take the idea of using compost tea in hydroponics. It will alter everything from your plants’ perspective.

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

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.

In order 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.

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.

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 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.

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 in order 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.

Mulder's Chart: Not proof of positive & negative plant nutrient interactions

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. 🙂

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

Hydroponic Plants are Vulnerable to Root DiseaseIt’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.

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.
Root Slime: Common Hydroponic Crop Proble
Vortex Compost Tea: Cures Hydroponic Root Slime in 48 Hours

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.

Root Growth 72 Hours After Compost Tea

New Root Growth 72 Hours After Compost Tea

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.

48 Hours Difference: Compost Tea in Hydroponics

48 Hours Difference: 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.

Hydroponic Nutrients Without Compost Tea vs. With Compost Tea

Hydroponic Nutrients Without Compost Tea vs. With Compost Tea

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 a suitable for making custom mixes. They are also more suitable for establishing healthy microbiological activity.

And if you’re 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 bioslimes, 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 illustration here were submitted by the author and may be subject to copyright violations published anywhere else.

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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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  • Mike Pomerantz April 13, 2017

    This is interesting. I started playing with an outdoor Kratky hydro method and did not use any Hydro nutrient solution. All I did was put the compost tea into the container and nothing else. I checked the pH, its currently sitting at about 7.5. Maybe a little high. I’m also using soil mix in the net cups instead of rock wool or pellets. In curious if all this together will create a successful plant.

  • Hi, Mike. The soil in the net pots is not hurting, but not sufficient to grow plants full term as the roots grow through it and any potting soil is relatively low in fertilizer to account for all plants without burning them.

    Compost tea is not a defined substance. Whether the compost tea recipe you are using will work as a complete fertilizer in hydro depends on the crop and the compost tea recipe. Generally, most recipes may have enough to provide base fertility for low feeders like lettuce, but would struggle to provide enough NPK for heavy feeders like tomatoes.

    For example, our recipe at is designed to be very forgiving at around 400ppm in clean water. While it contains literally every Earth-bound element available it does not have enough NPK to drive production. It’s purpose is to provide diverse soil microbes, micronutrients, and trace elements. It is a supplement to the base fertilizer. It is possible to make a recipe with fish, bat guano, etc that have more NPK but is a bit of an R&D trip to determine proper fertility, particularly in different stages of growth. Definitely try it, but it is not as simple or clean as artificial salts that are traditionally used in hydro. I should add it is also feasible to use compost tea to supplement salts, which is where the testimony above comes from.

    Hope that helps, happy to answer any further questions!

  • Also, what is the ppm of your nutrient tank?

    And while there is not a lot of explanation as to why, typically you do not need to pH balance the solution like you do with salts. The best I can do to explain is that Mother Nature makes it available, whereas with salts the chemistry does…FYI

  • Scott Lambert May 14, 2017

    That was the best explanation on this or these subjects that I’ve ever read. Thanks Evan, I’m going to start implemented this asap.. Cheers Scott (Brisbane)

    • Evan Folds May 17, 2017

      Thanks, Scott! Would love to hear results and be a resource as we grow. Be in touch!

  • Ryan Barfoot March 26, 2018

    Excellent article!
    I’m curious how compost tea could be used to grow microgreens on a soiless medium. I’m researching methods of microgreen production for home use and I’ve found a gap between the nutrient deficiency of growing in water versus growing in soil with the mess and large amounts of compostable waste (live in apartment with only 3 worm bins, not interested in cycling through bags of soil). This is the closest thing I have found toward filling that gap!
    My idea is to grow the most nutrient rich microgreens in fiber mats soaked in worm compost tea made by dunking and massaging a paint straining bag of microbe rich castings in water (method taught by soil food web certified instructor). Then misting only filtered water on the greens to avoid possible contamination.

    I’ve never grown microgreens and would greatly appreciate any insight and feedback.


    • Hi, Ryan. Sounds like a good plan. Having grown microgreens commercially in the past, I can tell you that we did not use compost tea in our operation. The reason being that the effort versus benefit didn’t seem to be worth it. Definitely don’t want to discourage your experimentation, as that is the name of the game, but the soil food web works on a longer time frame than is allowed in microgreen farming. The microbes simply don’t have enough time to set up shop and deliver their maximum benefit.

      The gap you are describing is real. The method you are describing would be termed a leachate or extraction, not AACT (actively aerated compost tea). AACT is a method of growing microbes to higher concentrations and is preferred when trying to maximize microbial populations for in-ground or longer term cultivation. Extraction would be good for your purposes, it is essentially “extracting” the soluble benefits of the worm castings into water for deliver to the growing plants. This may be all you need for fertilization, as, you are right, feeding microgreeens with water only, while possible given the short cycle term of their growth, is inadequate to deliver ideal nutrition. It is true that seeds have what they need for 7-10 days of growth with water only, but it is also true seeds have access to more than just water form soil in Nature. Better best.

      Finally, you may want to look into sea mineral fertilization. Sea minerals have all Earth-bound elements in a natural balance and make an ideal fertilizer for microgreens/wheatgrass/sprouts. The work f Dr. Maynard Murray and his book “Sea Energy Agriculture” would be a good source of info for you. Not geared towards microgreens, but will provide some background research on efficacy of using sea minerals as fertilizer. This is what we used in our microgreen operation.

      Hope this helps!

  • Really interesting all above .I do also my own experiments with a selfmade hydroponic system feed my plants with varius plants juice .

  • Hi, I am wondering if this is the same as bioponics. So, this is basically making compost tea all the time, filter the output and send it to the plant and return the excess back to the compost tea brewer, is it ?

    • Hi, Rafael. Yes and no. Rather than a defined process like “bioponics” the article is making the case for soil microbes and trace elements being included in conventional hydroponic applications. Sort of like “aquaponics”. Hydroponics has been developed around what the plant NEEDS, which is an entirely different concept regarding what the plant WANTS.

      I pioneered what I called “perpetual brewing” many years ago, primarily for retail garden centers that were using compost tea on a daily basis in varied amounts. Adding recipe ingredients back to the brewer based on the amount of water added over time allowed for the brew to continue and to save the ingredients that were not used or sold for the future. It is not necessarily a process that makes sense for growers who can brew up a targeted batch and add it to the system weekly, for example. You could use a “bioponic” approach if you want, or you can simply add 1 gallon of compost tea concentrate to 20 gallons of reservoir solution over time as a replacement or top off and be introducing soil benefits to the hydroponic application.

      Then of course, you would want to define the compost tea recipe for the crop and stage of growth. My approach was always to make a general recipe that was not crop or stage specific that can be used as an “all purpose” with the base fertilization being delivered through conventional means.

      Thanks for the question, hope this helps!

  • My commercial grow company uses dwc and did well using compost teas for the first few weeks of flower and then root rot set in each time by wk4.
    We battle with hypochloric acid and h2o2 flush and then introduce the nutrients back in. We’ve seen that reintroducing a new batch of tea only makes things worse. We are back to using top feed drippers and wicking the net pots.
    I use teas successfully all the time with my tlo growing and super soil mixes. Any help would be wonderful.

  • What would be the right percentage of compost tea in relation to the water (i.e. 10 gallons of water) in the hydroponic system? Or should it be 100% compost tea?

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