What is Compost Tea?

There are so many nuances to what compost tea is. And certainly, a lot of confusion. This article aims to clarify, teach, and inspire you to learn about compost tea and make it yourself using the compost tea recipe near the bottom of the page.

Compost tea is the liquid form of decayed organic matter (compost) that we apply to improve plant growth. Its main goal is the cultivation of diverse beneficial biology to support soil fertility and ultimately the growth of healthy plants.

But first, why care about compost tea in the first place?

There are indeed so many benefits to learning about and using compost tea, but ultimately, the goal is to improve plant growth and production. Along the way, we improve so much more. Producing compost tea:

Now that we’ve figured out the benefits, let’s go back and refine our definition of compost tea.

Dr. Elaine Ingham, renowned soil scientist and main proponent of the idea of a soil food web answers the question, “What is compost tea?” in the USDA’s Soil Primer.

“The simplest definition of compost tea is a brewed water extract of compost,” Dr. Ingham says.

She qualifies the term “compost tea” with technicalities that are often lost on the everyday gardener and farmer.

A common practice among compost tea brewers is the addition of food for the microbiology in the tea to grow to levels far beyond what they normally would in compost alone.

Dr. Ingham proposes that compost tea made without the addition of food for the biology to develop is not compost tea at all, but merely a “compost extraction.”

Despite Dr. Ingham’s specific definition of compost tea, you’ll find published research calling both compost tea (fed) and compost extraction (not fed) by the same name: compost tea.

According to Eric Fisher, author of “Compost Teas for the Organic Grower,” “Compost teas are either aerated, non-aerated or a combination of the two. Aeration is simply the process of applying oxygen to a solution. In the absence of atmospheric oxygen, anaerobic processes take over.”

We try to keep away from cultivating anaerobic bacteria (bacteria that can survive at low or no oxygen levels) because many of these types of bacteria are harmful to humans.

Compost research specialist, Troy Hinke’s description of compost tea is “a liquid form of compost that provides soil and plants with beneficial biology.”

This sounds simple enough.

He adds that the purpose of compost tea is “to provide plants with nutrients and disease suppression (capabilities).”

What we’re trying to do is pull out all the beneficial micro-organisms that are in good compost into water, and then send them off to support our crops.

So if the liquid compost doesn’t have good bugs in it, it’s no good.

As alluded to above, there are a few kinds of compost teas/extractions to note. The main categories are:

Activated Aerated Compost Teas or (AACTs) are compost teas that are fed “microbiological food” before they’re brewed or aerated. During the brewing process, oxygen is bubbled through the tea, and the amount of oxygen in such a brew should be greater than 6%.

The foods that are commonly used to increase microbial levels are blackstrap molasses, fish hydrolysate, yeasts, corn meal, brown sugar, humic acids, and powdered kelp.

Of these biological foods, compost tea experts generally discount molasses or sugars since they increase the numbers of aerobic bacteria, while also increasing the numbers of anaerobes and pathogens (should the original compost from which your tea is derived happen to be pathogenic).

But what if we didn’t feed the biology in our compost teas? Would the effects still be the same?

Soil Test Results for Vermicompost:

Test Results for Vermicompost Extract (Brewed but not fed)

The soil tests above show that there is a significant drop in biology when I brewed my vermicompost into what is sometimes referred to as Aerated Compost Tea or ACT or “compost extract” by those who have undergone Dr. Ingham’s Soil Food Web programs.

This is where the literature gets confusing. Those educated by Dr. Ingham, adhere to using the technical term “compost extraction” instead of “compost tea.” But published research will sometimes cite Aerated Compost Tea (ACT) and not mention feeding the biology supplemental nutrients.

For Dr. Ingham and her students, compost teas that aren’t fed are always just extractions, even if they’re aerated.

To help clarify this term, I sent two vermicomposts and vermicompost tea/extraction samples to the Soil Food Web lab nearest me to get an idea of what kind of life I was indeed brewing in an unfed compost tea solution. I found the following results shown above.

As you can see from the images above, the microbiology of my vermicompost tea/extraction is significantly reduced. Despite being aerated, the good guys just didn’t survive without having been fed anything.

Why, you may ask, should you choose not to feed your compost tea?

A study by Dr. David T, Ingram of the USDA showed that adding any biological food whatsoever to your compost tea before brewing increased pathogenic growth to dangerous levels provided there were indeed pathogens like E.coli and Salmonella in your compost in the first place.

However, brewing without supplements showed that even when there were pathogens present that these bad guys would become negligible after the brew and be far outnumbered by the good bacteria.

Basically, if you feed bacteria sugar, good or bad, they like it and will grow! But if you don’t feed them, at all your compost tea will be safe but your beneficial microbiology population may not be high enough to benefit your crops.

How can you be sure your original compost is pathogen-free?

Test your compost and water for the presence of pathogens by:

Some things to note, studies have shown that the red wriggler composting worms (Eisenia foetida) used to make vermicomposts, greatly reduce pathogens. Looking at my own vermicompost above, my specific sample showed no pathogens present!

The National Organic Program (NOP) offers the following guideline to ensure that compost tea made from hot/thermophilic compost is pathogen-free:

Compost tea extractions or compost extracts are the results of plunging your compost in water (around 2-4 cups in the 5-gallon bucket or 1 gallon of compost per 50-gallon brew) and massaging your semi-permeable mesh bag so that you extract the biology that lives on the surface area of the soil.

Break up clumps and move your compost bag so that you can break the material as small as possible and use it in a compost extract. According to Dr. Ingham, you can get an extraction in as little as 15 minutes, but the more your “steep” our compost, the more concentrated your extract becomes.

In herbalism terms, this would be called an “infusion.”

So the longer you steep, the better, but steep it no more than 12 hours without aeration, so that you don’t end up with an anaerobic brew.

Repeat this 1-2 more times to get a stronger extraction.

Remember that according to Dr. Ingham, even if you brew this concoction, this is still technically, a compost extract as you’ll not be feeding this biology.

This is the type of compost product that you do not want to use. These are the dregs and drippings of compost that collect at the bottom of your compost bin and are likely to harbor pathogens.

You can never be sure how long it’s pooled at the bottom of your compost container and whether or not it has gathered and cultivated any bad bugs along the way. This is why it’s best not to use leachate from your compost bin and run the risk of contaminating your crops.

In a podcast, garden author and host Christi Wilhelmi shared an anecdote of how she tested the effectiveness of leachate and had all of her plants die quickly after applying leachate to them.

One client from the Permaculture Gardens Grow-It-Yourself Program, recently purchased a Compost Tea Brewing Kit, only to determine, she did not like the sound of the motor running in the back of her house for 24 to 48 hours.

So she decided to ditch the pump and simply steep her compost in the mesh bag, stirring it occasionally to extract the biology into the water.

This way of making compost tea is known as the Bucket-Fermentation Method and the brew time for this is typically from 7 to 10 days. According to compost tea researchers, Steve Diver and Dr. Ingham, this method dates back hundreds of years in Europe and is more akin to a compost watery extract than a “brewed” and aerated compost tea.

Now we get to the practical part.

Making your own DIY compost tea is simple.

Don’t be fooled into thinking that the drone of a fish tank pump complicates the process. As long as you have an aquatic pump that has a flow rate of 715 GPH (gallons per hour), a 5-gallon bucket, a mesh bag, and some good compost, you can make compost tea.

Requirements for finished compost are detailed by the National Organic Program as follows: “The compost pile is mixed or managed to ensure that all of the feedstock heats to the minimum of 131º F (55º C) for a minimum of three days. The active composting process is finished when the pile returns to ambient temperature levels.”

The time of “finishing” your compost can also vary if your compost is thermophilic (heats up to 131F) or a slow-burn “cold compost” that just sits there and is ready in as little as four months to one year. Other factors that affect the “curing” time are moisture and temperature.

The end result should be that they smell rich and earthy and not stinky. If your compost is stinky, that’s a sure sign that something has gone awry in the composting process.

There are many compost tea recipes out there but in this one, I would like to propose starting with vermicompost because:

If you start with a vermicompost base, you’ll be brewing a more bacterially dominant (good for leafy vegetables) compost tea with the following recipe:

To make your own DIY compost tea prepare the following:

You can use your tea as a root drench or a foliar spray to increase nutrient absorption and stimulate your plants’ immunity.

Given that your compost tea microbial population is at adequate levels, you can use 5 gallons of compost tea, per acre. If you know that there is not much life in your soil, water your garden with the tea every week until you see positive results in plant growth.

Dr. Ingham provides similar guidelines for compost tea applied as a foliar spray in her Compost Tea Brewing Manual:

“If tea is within the desired range indicated on the Soil Foodweb report, then it can be used at 5 gal/ac (50L/HA). If organism numbers are greater than this, then the tea can be used at a lower rate, relative to how much it can be diluted based on getting adequate coverage on the leaf surfaces.”

Be sure that you have passed your compost tea through a strainer or sieve to remove particles that can clog your backpack or hand sprayer before you use it as a foliar spray.

Despite what many gardening blogs say about compost tea not being worth the time, I can say that I have seen enough evidence in conducting research and observing my own garden to support compost-tea-making as a cost-effective and time-saving way to grow abundantly. It is much easier to outsource the work of growing plants to the beneficial microbiology in the soil than trying to figure out every detail myself. The best way to do this type of outsourcing is to cultivate these microbes through compost tea.

These good bugs know much more than us about what needs to happen to make good fruits, veggies, and flowers grow!

This means a little compost will go a long way. Remember to use unchlorinated water before brewing to avoid killing the good microbes.

Once you stop the aeration of your tea, you’ll want to use it immediately before the biology dies or worse, harbors pathogens.

There’s an ecosystem below ground that supports the ecosystem above ground. It’s about time we pay attention and work with the soil life to help them support our lives. Compost tea is a simple way that we can work with that soil and plant ecosystem. Go and give it a try!