Compost Tea

Notes from Various on compost tea

Source:      Tim Wilson of Microbe Organics

Why use compost tea?

The main reasons for using compost tea are;

1/ to provide a quick nutrient kick to the rhizosphere. This works mainly because as the flagellates (protozoa) consume the *bacteria/archaea they utilize only 10 to 40% of the energy intake for their sustenance and the remaining 60 to 90% is expelled as ionic form nutrient which is directly bio-available to the roots of the plants. This is known as ‘the microbial nutrient loop (cycle)’.

2/ to begin or continue an inoculation of the soil with a microbial population. Many of these microorganisms will go dormant until called upon later to fulfill their purpose but many of them will grow and flourish, finding their station in the hierarchical positioning of microbes in a living soil. Some, like the fungi will grow out through the soil binding aggregates together, assisting with air and moisture retention, providing pathways for bacteria/archaea, providing a food source for various microorganisms and degrading organic matter to a point where it is available for other organisms.

Within a very diverse ACT there will be free living nitrogen fixers, anti-pathogens and yes a few of the anaerobic and facultative anaerobes which serve their positive role in a living soil.

3/ to potentially provide the microorganisms which may assist in protecting plants from pathogens.

4/ because it allows the use of less [vermi]compost over a given area. There is nothing wrong with using only [vermi]compost instead of ACT if you have that much. ACT just allows you to use less [vermi]compost and it accelerates the microbial process.

*Note; I use the term bacteria/archaea because without complex testing it is not possible to visually tell the two apart. Recent research has revealed that archaea are commonly found in soil worldwide and have just as an important function in the microbial nutrient cycle as bacteria.

Recipes and Technique;

In case I have not been clear enough above, our goal in making ACT is to extract,  multiply and grow mostly aerobic microorganisms in as large a diversity as possible and inclusive of three basic groups; bacteria/archaea, protozoa [flagellates & naked amoebae] and fungi. (Some [vermi]compost will contain rotifers which are extracted into ACT. These cycle nutrients in similar fashion to protozoa and are a bonus if present.)

Making ACT is not about putting in ingredients which directly benefit the plants. The foodstocks used are strictly to feed or benefit the microorganisms which in turn benefit the plants.

When I jumped on the compost tea bandwagon years back I utilized the whole gambit of ingredients recommended by the current (at that time) supposed authorities. These ingredients or foodstocks included, humic acid, kelp meal, black strap molasses, baby oatmeal (oat flour), fish hydrolysate, alfalfa meal, etc. We used variations of these ingredients in our 1200 gallon ACT maker on our farm and microscopic observation showed success.

I also experimented with using some rock/clay powders as ingredients and observed differences in the microbial make up which had positive results applied to the soil and plants. The types used were mostly soft rock phosphate and pyrophyllite.

Along the line somewhere we left humic acid out of a brew and noticed an increase in microbial numbers so we stopped using it ourselves but, possibly irresponsibly, I continued to recommend it because the ‘bigwigs’ did so. It was not until I devised a method to test each foodstock independently that I began to change my tune and begin to go against the grain of the contemporary experts.

By testing some ingredients independently in a liquid I observed;

1/ that humic acid in varying dilutions does not feed any sort of microscopically visible microbe. I observed that it actually suppresses microbial division and growth. This was confirmed by joint testing with Keep It Simple Inc. (KIS) in the Seattle area. We tested two of the most effective and popular brands. I cannot say definitively that all brands of humic acid will have similar suppressive effects in a liquid (ACT) but it is enough for me to discontinue using it or recommending it as an ACT foodstock. Please note that this does not mean that it is not good to use on/in soil….just not ACT.

2/ that kelp meal initially delays all microbial development in a liquid but does feed fungi and bacteria/archaea following 24 hours. If too much is used the effects are suppressive. From this I garnered that it should be used very sparingly and one must be prepared to brew a little longer if using this foodstock. Again, this does not mean that kelp meal is not a good thing to use in/on soil. It definitely is!

3/ black strap molasses (BSM) feeds both bacteria/archaea and fungi equally well contrary to what the A(A)CT aficionados were saying. The story was that BSM feeds only bacteria. This led to all sorts of misconceptions, even including ones made by USDA and Canada Agriculture scientists who declared that using molasses in ACT could lead to e-coli contamination. It is utter nonsense. Besides the testing I have done and ratifying assays carried out by KIS, it is common knowledge amongst many mycologists like Paul Stamets that BSM grows out fungal hyphae just fine.

4/ fish hydrolysate feeds both fungi and bacteria/archaea again contrary to the story at the time that it is mainly a fungal food. (I’m glad to see that story has now changed)

5/ alfalfa meal is also a decent all round foodstock which sometimes introduces protozoa cysts to the ACT. KIS has done more testing on this than I have.

The result of all this is that my attitude towards recipes for ACT has really evolved over the years with a trend towards the more simple. I know that there are a lot of people who place importance on creating a bacterial or fungal dominant ACT. At one time I myself was so influenced, however, the more I’ve learned and unlearned about living soil and a functioning microbial population interacting with plants, the more I’ve been led to allow the soil and plants to decide which microbes are actively needed by the rhizosphere team. What this means is that 9 times out of 10 I’m trying to create a balanced ACT with a decent ratio of the three basic microbial groups. When this hits the soil, some will go dormant to wake up later and some will be immediately put into action at the direction of the needs of the soil and plants.

The exceptions to this may be if I am attempting to battle a particular pathogen and want to attack it with a heavy fungal or bacterial (or a combo) ACT. In these situations some tweaking of recipes and timing can be helpful. If attempting these variations, a microscope is really the only way to confirm the desired microbial population. I have outlined some recipes which may trend towards a certain microbial group (or combo) or may assist with certain pathogens.


Through a plethora of trial and error brewing with a dissolved oxygen meter at hand we determined that a pretty reliable volume of [vermi]compost to use is 2.38% by volume of water used up to around a 250 gallon brewer.

So if you have 5 gallons you multiply that by 2.38% to get the amount of [vermi]compost to use. Then you can go to;  and convert it into any unit of measure which is convenient. In my opinion measuring [vermi]compost by weight is inaccurate because of varying moisture content.

Anyway to proceed we have;

5 x 2.38% = 0.119 of a gallon = 0.476 of a quart = 0.450 of a liter
= 450.5 milliliters [450 rounded] = 1.904 cups [2 cups rounded]  – Your choice

Likewise with the use of black strap molasses, a percentage of 0.50% is a good median amount to use.

These two ingredients, perhaps surprisingly, comprise the total of inputs in most of our brews these days. This simple recipe, if using an efficient ACT maker and good quality [vermi]compost results in a microbial population made up of the important three groups. This is the only recipe used to date, in all the videos on my Youtube channel ‘Microbe Organics’

To get these three groups the ACT maker should be run for 36 to 42 hours. The ideal temperature range is 65 to 72 Fahrenheit (18 to 22 Celsius), however a little cooler or warmer is okay. I’ve had pretty equivalent results with ambient temperatures around 100 F (38 C) and as cool as 50 F (10 C).

To spill a small secret, I’ve been pre-feeding or pre-activating [vermi]compost which is not so fresh by mixing in a small amount of wheat bran (livestock store or bulk foods department grocery store) and moistening with very diluted black strap molasses, loosely covered with cloth or paper towel 24 hours ahead of brew. (approximate ratios, wheat bran 1:30 [vermi]compost & BSM 1:300 water).

This has, so far resulted in (most of the time) attaining the desired microbial population at 24 hours brew time rather than the usual 36 to 42 hours.

Now for some of my other recipes;

A recipe for a balanced nutrient cycling ACT which many growers claim to have great success with is;

[vermi]compost – 2.38%

unsulphured pure black strap molasses – 0.50%  [but you can use a maximum 0.75%]

fish hydrolysate (high quality) – 0.063%
Do not use chemically deodorized liquid fish!

kelp meal – 0.25% max. [Less is more!]
NOTE: This is a maximum amount of kelp and you can experiment using less. This is using regular grade kelp meal for livestock. If you have soluble kelp, I recommend using smaller amounts. As noted earlier kelp meal can initially delay bacterial multiplication and fungal growth in ACT.

soft rock phosphate granules/powder – 0.063% Consider this optional. In the past 2 years I’ve become more aware of the possibility of polonium 210 and lead content in soft rock phosphate which is radioactive. This varies depending on how it was mined and where. If you wish to use this in ACT check all available data. Look for heavy metal testing
We grind up the granules into a powder with a coffee grinder

The brew time should average around 36 hours and no longer than 48 hours. If you have a microscope then stop when the microbes desired are observed. Otherwise smell for the foodstocks being used up, possible rank odor (indicating anaerobes) and a positive earthy or mushroom-like aroma.

Fungal Brew;
If you want a brew which is more fungal increase the amount of fish hydrolysate to around 0.19% and you may wish to decrease the amount of molasses used so there is not a foodstock overload. Include a pinch of alfalfa meal, not using more than 0.25%. It is important to not overload a brew with foodstocks, otherwise you can easily compromise the dissolved oxygen capacity of the unit. Most importantly discontinue brewing around 18 to 20 hours. Of course if you have a microscope you can judge that for yourself.
Also, if you do not have fungi in your [vermi]compost, you won’t have it magically appear in your ACT.

A Few Extras;

I sometimes include a pinch or handful [depending on brewer size] of sphagnum peatmoss in a brew. Depending on where the peatmoss was harvested, it will contribute a set of microbes somewhat similar to that derived from the ‘Alaska’ humus or humisoil products on the market. It is a least a better bang for your buck and at best a trifle better quality-wise.

I’ve had inconsistent success battling powdery mildew by including soft rock phosphate and pyrophyllite clay powder, both at 0.063% in a 24 hour brew with horse manure fed vermicompost, BSM and fish hydrolysate. I have observed a very tiny peanut shaped bacteria/archaea in vast numbers with this recipe. In the ACT they are very active and appear to feed on yeast. This has led me to hypothesize that they ‘might’ be devouring powdery mildew but at this point that is pure conjecture.

Replacement for Molasses:

I’m continually getting this question. What can I use as a replacement for molasses?
Many people assume that molasses is just sugar and propose using various forms of sugar in its stead. This may actually work to some extent, however black strap molasses is a complex carbohydrate bearing lots of minerals and nutrients plus it is a powerful antioxidant. [some nutrient companies will happily sell you a bottle of carbo this or carbo that when it is actually just molasses, in some cases watered down]

I’m not saying there are not other foodstocks which can be used to feed bacteria/archaea and fungi. Heck, you can grow out some bacteria with potato water or rice water.

What I am saying is that black strap molasses works for the simple process of multiplying bacteria/archaea & fungi so why fret about using something else? If you are somewhere that you cannot get any, then by all means try something different or if you have a scope, go ahead and experiment.

I guess if I was stuck without molasses, I’d try wheat bran.

Mesh Bag or Free Suspension:

This is another decision when making ACT or designing an ACT maker. Do I throw the [vermi]compost into the water and let it float around or do I put it in a mesh extractor bag of some kind?

There are pros for both. Generally one gets a higher density of microorganisms if you just dump all your ingredients into the aerated, agitated water. I have observed over and over microscopically that this is the case. If you are using this method with an ACT design which circulates the water through a pipe like an airlift be aware that big chunks will plug up the pipe. Use fine [vermi]compost for this.

ACT made this way is most appropriate for applying to your soil but what if one wishes to spray it onto leaves? Perhaps you are trying to combat powdery mildew. Perhaps you want to run your ACT through an irrigation system.

This is when you are perhaps going to consider using a mesh bag. I researched many different mesh openings and materials before concluding that a 400 micron monofilament nylon mesh is the best for an extractor bag. This is also the size recommended by SFI. This is what we provide with our 50 gallon airlift brewer (as an optional configuration).

If you cannot find the perfect 400 micron mesh bag, don’t sweat it. Just get a paint strainer from the hardware store and tie it off with the ingredients and airline in it. Please do not use nylon socks/stockings. These usually have too small a mesh size to extract fungal hyphae (unless they are recycled from your 400 pound grandmother). Many people argue for using these by saying ‘hey man how big do ya think bacteria are?’ My reply to that is ‘hey man, bacteria is only one component of ACT’ What about the protozoa besides the fungi already mentioned?

If one does use a mesh extractor it is essential to either use a smaller (e.g. 5 gal) ACT maker which has enough agitation to make that bag dance or to use an air (diffuser) input into the bag.

If you have a cone bottom airlift bioreactor and you wish to use a mesh extractor, I recommend using a separate air pump to supply the bag.

I prefer to use a diffuser in the bag but many just use an open airline. I’m a believer in using what you have (except for chemicals). If you use a mesh bag you do not need to worry about a few large chunks. Many people make good quality ACT this way.


There is another option. Say you have an airlift vortex ACT bioreactor but to run it with a mesh bag would be kinda silly. You want to run it through a sprayer or irrigation set up. If your unit has a drain valve/spout, then just put a pail under it with a piece of mesh tied across the top. For this we use nylon window screen (800 to 1000 microns mesh size). Because some residue will block the passage we do not want to use 400 microns for this. Open the valve and as organic matter builds up on the screen scoop it off into another bucket. This prevents a build up which will block microbes but also allows you to save the ones that do get blocked, along with the organic matter for topdressing your soil or throwing into the compost pile. You can obviously see why a filter internal to a pipe or hose just won’t work.

Okay, I know that sounds like work. There is another way…the way we do it. Just empty out your ACT maker into the pail, use a mesh bag (800 to 1000 microns) with a sump pump dropped into it, hook the sump pump to a hose. There is your sprayer or waterer or irrigation hookup. When we don’t care about getting residue on leaf surfaces, like our corn or the lawn, we use a trash sump pump with no bag and a thumb over the end of the hose.

Frequency of Use;

You can use ACT as much as you wish. We often used it almost every watering. Just don’t waterlog your soil.

A friend of mine who used actual living microbial soil (ALMS) as opposed to truly living soil (TLO)…hehe, um used ACT for 7 years to beat back an erwinia infection caused by using chemicals in his one acre garden. The infection was gone in the first year but he liked the increased quality so much that he built a 5000 gallon ACT maker (venturi) and used it through his irrigation system. In the 8th and 9th years he only used it once as the microbial population was so well established and his soil had matured to the point where it was no longer necessary


This is another question I get all the time. How much should I dilute my ACT?
Now this is a difficult question to answer. I believe that SFI has stated that 20 gallons can be diluted to do one acre. In my opinion, this is stretching it but is within the realm of possibilities.

When diluting ACT it is not the same as diluting fish hydrolysate or molasses or (saints forbid) a liquid fertilizer. The water is not ‘weakening’ a solution so much as acting as a carrier for the microbes which you have multiplied. Logically though, if you do not have a ‘tea’ very dense with microorganisms, adding it to water will make it even less dense. So your 5 gallon ACT diluted down enough to cover the quarter acre is still going to get the microbes out there but in much lower numbers.

When we use ACT on our farm our usual practice is to apply it non-diluted, followed by irrigation water if necessary. When we were on the larger farm, we used a 1200 gallon multi-airlift brewer and pumped it straight into the irrigation system, then followed by water. We found that this was enough to do our greenhouse (20 x 64) and a quarter (approx. 750 sq. ft) of our outside beds. A total of just over 2,000 sq. ft. One acre is over 40,000 square feet.

For curiosity (on our little farm where we are now) we diluted 12 gallons of ‘tea’ into 40 gallons of water prior to use, this past season. I looked at it under the microscope before and after and although the microbes survived, they were indeed much more widely dispersed.

I guess the moral of the story is that you can dilute your ACT if you so wish but I think it is better applied non-diluted, followed by water ‘only if necessary’.

Adding Ingredients to a Finished Brew;

As I’ve mentioned we used to make 1200 gallon batches of ACT which we applied on our farm garden beds through an irrigation system. We used the same tank if we wanted to apply some other diluted soil amendment or fertilizer, like fish hydrolysate, molasses (occasionally) or humic acid.

I had read that many growers and landscapers were adding some of these amendments into their ACT just before applying and I believe this process was endorsed by SFI. Anyway we decided to try saving some time and money and dumped 5 gallons of fish hydrolysate into a 1200 gallon batch to pump out. I had, as usual examined the finished brew microscopically and out of curiosity took another sample after mixing in the fish hydrolysate. To my astonishment and dismay I had wiped out or put to sleep almost half of the microorganisms. This was the last time we did this.

We always apply amendments separately from ACT and this is what I recommend unless using the most minuscule amounts. I surmise that adding anything to a finished brew can have similar negative results. The amount of FH we used was 0.4%. If you have a microscope, go ahead and experiment.

Review of Some Common Myths; [In no particular order]

1/ Small bubbles destroy fungal hyphae or other microbes.

This is utter nonsense. The bubbles/air would need to be super compressed to harm any microorganisms.

2/ Molasses should not be used or only feeds bacteria.

Black strap molasses (BSM) is a complex sugar/carbohydrate and feeds bacteria/archaea and fungi equally well.

3/ Fungal hyphae is difficult to grow in ACT.

If you have fungi in your [vermi]compost and have a decent brewer design and use 0.50% BSM it will grow out in the first 15 to 20 hours along with bacteria.

4/ You can have too much air/agitation in a compost tea maker.

This would only be true to the extreme…if your water was jumping out everywhere. If a salesperson is telling you microbes need gentle bubbling, they do not know what they are talking about.

5/ One can make good ACT with an aquarium pump in 5 gallons of water.

We did almost a year straight of research (at a cost of thousands of dollars) building almost every conceivable compost tea brewer design and size, ranging from 1 to 1200 gallons. These included every type itemized on my webpage in the design section and more. We measured the dissolved oxygen (DO2) religiously at all hours of day and night, eliminating configurations which failed to maintain the DO2 at or above 6 PPM. This is close to the minimum level required to support aerobic organisms.

The outcome of this research was, the estimation, that the minimum flow required from an air pump to make compost tea while maintaining the DO2 at 6 PPM, is 0.05 CFM per gallon while the optimum flow is 0.08 CFM per gallon or greater. (the only exception was when utilizing airlifts)

This means that most aquarium pumps will not work with a 5 gallon ACT maker, no matter what a couple of guys from Texas say. Two gallons, perhaps.

6/ Nematodes are a common microbe in ACT.

I’ve received many emails from folks distraught over the fact that they found no nematodes in their ACT or that they had very few. This is normal. Unless you happen to have a species of nematode which is an aquatic dweller, (rare in compost wouldn’t you think) you are very unlikely to have many surviving in ACT over 4 or 5 hours old. Why? Because they drown. A few will survive, which accounts for some making it to the end. Even companies which sell nematodes instruct customers to not leave them in the distribution water more than two hours.

I’m pretty sure that this myth originated with SFI but even they (Dr. Ingham) have now changed their tune and say ACT is not a good environment for nematodes.

7/ You can tell that your ACT is finished or ready to use when it forms a head of foam.

More bunk! But this does have a bit of foundational truth. Foam can be formed by proteins in the water created by microbial activity, however this is not a reliable indicator. Foam can also be created by saponins (aloe vera, alfalfa, yucca) or just by adding molasses or by worms which might have made it in there. I have examined very foamy ACT microscopically which was practically devoid of microbes and ACT with no foam at all which has been swarming with microbial activity.

The best bet to tell when ACT is finished is to use it between 24 and 40 hours, smell it to make sure it has not gone anaerobic (you’ll know) and that most of the foods you added have been consumed. It should smell earthy or somewhat like mushrooms.

I’m not sure how this myth got started but it sure took off.