Worm Tea & Extract: An In Depth Guide
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Time to read 19 min
Table of contents
Worm Tea & Extract as Biological Amendments What Is a Compost Extract vs. a Compost Tea? Why Extracts Win 90% of the Time How to Make a High-Quality Compost Extract How to Make Quality Worm Tea Choosing Your Brewing Equipment Proper Aeration: The Rolling Boil Rule Making a Tea Recipe Worm Leachate, Worm Pee, and Vermiwash Quality Assurance on Your Extracts and Teas Worm Tea & Extract Application Methods Soil Organic Matter is Critical to Success Frequently Asked Questions (FAQ)
Worm Tea & Extract as Biological Amendments
The true value of worm castings isn't in their NPK rating - it’s in their living microbiology.
At roughly 1-0-0 NPK, relying on castings for direct chemical nutrition would require an absurd 20,000 dry pounds of worm poop just to supply the 200 pounds of nitrogen needed for an acre of corn.
But worm castings aren't a traditional fertilizer; they are a high-density biological inoculant. A single handful can contain billions of beneficial bacteria, miles of fungal hyphae, and essential protozoa and nematodes that drive natural nutrient cycling, build soil structure, suppress disease, and unlock bound soil minerals right at the root zone.
Unlike soil nutrients, microbiology reproduces. This is why soil health pioneers like Elaine Ingham, Nicole Masters, and David Johnson advocate for application rates as low as one pound per acre. You just need to get a very small amount of the rich soil life in your castings inoculated into the soil for them to start making more and more of themselves, and eventually colonize the soil.
Though there's obviously more nuance to it than that, but the idea with liquid extracts, like worm tea and worm extract, is to take the massive microbial workforce off the solid castings and suspend it in water so that it can be applied across acres at a time.
So if your goal is to heal soil on a large scale, liquid amendments are the way to go!
What Is a Compost Extract vs. a Compost Tea?
The fundamental difference between an extract and a tea comes down to two simple factors: time and added food.
A compost extract is simply water that has been moved through worm castings to strip the beneficial microorganisms, humic and fulvic acids, trace elements, and plant growth compounds off of the them to be held in suspension in the water.
It takes a matter of minutes to make, requires minimal equipment (a bucket or tank, water, and preferably a 400 micron mesh bag or screen if you are applying it through any spraying equipment), has a longer shelf life, and is pretty much impossible to mess up.
A worm tea starts as an extract, but then you add fresh food and supply continous oxygen for the microorganisms to drive a microbial bloom.
The process takes 12 hours at the minimum, requires more equipment, and is a much more volatile process, making it less shelf stable, and easier to mess it up.
Why Extracts Win 90% of the Time
The core argument for brewing a tea is that you end up with "more" microorganisms. But high-quality worm castings already contain a booming, hyper-diverse microbiome. Soil microbiologists and commercial practitioners are increasingly pointing out that there is already so much biological activity in a raw extract that you don't need to force a fresh microbial bloom.
And that microbial bloom might be what turns a good extract into a bad tea. Microbes consume oxygen as they grow, and if they grow too rapidly they can consume available oxygen, turning the tea anaerobic which can harm your plants rather than helping them.
But even if you do have a microbial bloom, and your tea stays aerobic, odds are that its just a handful of species that "bloomed." Zack Jones at Aggregodata has done work sequencing the bacterial communities in extract, then compared them to the communities once that same extract has become a tea.
Bacterial sequencing of an extract
That same extract after being turned into a tea
As you can see, even when "successful" a tea is going to favor a small group of organisms far beyond the others and have a negative impact on your diversity.
Now there are situations where you can manipulate the tea microbiome to your favor if you have a decent way to monitor it. For example, I have been able to take worm castings that were a bit more bacterial dominant than fungal, and with some time as a tea, was able to change the microbiome to be fungal dominant by feeding fungal foods and timing the use of the tea for when protozoan numbers were highest. I explain this in a bit more detail in my worm casting microbiology video I did with worm people on youtube.
But for 90% of the time, it seems that if you want more microbial biomass in your liquid application, the easiest and safest way to do it isn't to make a tea, but to just add more worm castings - especially since you're hardly using much anyway.
Either way, we will cover both how to make an extract and a tea in coming paragraphs.
How to Make a High-Quality Compost Extract
The first step to making a high quality compost extract is sourcing high quality compost. If you need your own compost or worm castings tested, or want to find sources of high quality compost near you you should check out soil microbiology page which can help with either of those.
And once you've done that, you've done the hard part!
Method 1: The Mesh Bag Massage (Best for Small Scale)
- Place high-quality worm castings into a 400-micron mesh bag.
- Submerge the bag in a container of water. Dechlorinated is ideal, but not necessary.
- Massage water through the bag underwater for a minute at most. You should see the water rapidly turn a rich, dark coffee-brown color as biology and humic compounds release.
Alternatively, if you have a compost tea tank and bubbler, you can let the air pump do the work and just leave the bag of worm castings/compost in the air column where the bubbles will pull off the biology as seen in my video here.
Method 2: The Bucket & Paint Mixer Method
- Add worm castings directly into a bucket of water.
- Use a standard drill-mounted paint mixer to rapidly swirl the water for a few minutes.
- Pour the liquid through a fine mesh screen or strainer bag before pouring into your sprayer or irrigation tank if you are using one.
Method 3: Spraying with a Hose
- Place your worm castings in a bag over a bucket or something that will catch the resulting extract.
- Spray it with a hose. It will need some pressure, placing your thumb over the hose end should be plenty.
Can't get much simpler than that!
This is also how some commercial extractors work. They use targeted water pressure from a hose to wash water directly through a basket of castings, flushing the extracted liquid straight into a receiving tank. You can replicate this on a farm using a hose nozzle and a fine mesh collection basket.
How to Make Quality Worm Tea
Choosing Your Brewing Equipment
Just the same with an extract, the first "equipment" you'll need is quality worm castings. Check out our soil microbiology page if you need help with that!
Next, you'll need a pump and tank.
Conical-Bottom Tanks are Ideal. Your tea is a mix of water, organisms, and microscopic pieces of organic matter from the castings, and also whatever you feed the tea. Unless they are agitated, the heavier particles (fungi and organic matter) will settle to the bottom of the container and stay there. Conical bottoms force solids to continuously slide down into the center point of aeration, ensuring total suspension and elimination of oxygen-deprived pockets.
For your airflow, you just need something that will create a rolling boil on the surface of your water. Aquarium pumps work with small set ups and regenerative blowers for larger set ups.
Keeping your equipment clean is important, and ease of cleaning should be part of your decision. Choose tanks that you can easily reach inside and through to clean it. Don't clean it with any abrasive materials if your container is made out of something that can be scratched - creating places that biofilm can accumulate and contaminate future teas.
For your air source, air stones are never a good option. It is too difficult to clean inside of an airstone, and your sticky feed ingredients and microbiology will get stuck up in there and create little pockets of anaerobic goo that will contaminate your future teas.
Proper Aeration: The Rolling Boil Rule
Unlike extracts, teas require active quality assurance before application to ensure you haven't brewed an anaerobic or pathogen-heavy liquid.
Your air pump should create enough physical agitation to resemble a soft "rolling boil." It should not generate bubbles so violent that they are creating many splashes out of the container. The level of agitation in my video above is slightly too much, but not too bad.
Making a Tea Recipe
Truth be told, I am a molasses hater, and explaining why will help you choose what foods to use in your tea recipe because it epitomizes a bad choice of tea ingredients.
Molasses is a simple sugar, and simple carbon compounds like it feed a narrow group of fast-growing, opportunistic bacteria, completely overgrowing and smothering the fungal biomass, protozoa, and beneficial diversity present in your original material. That sudden bacterial bloom consumes dissolved oxygen rapidly, which can cause a total crash, and in that oxygen-starved and sugar rich state, you can get all sorts of nasty microorganisms growing.
Its also commonly recommended in tremendous amounts, as much as 1-2 tablespoons per gallon. In my own tests, I found that if I added more than 3.12 mL of fish hydrolysate per gallon of water then the tea would show sign of becoming anaerobic. 2 tablespoons of molasses is nearly 10 times that amount, and is much more quickly decomposed than fish hydrolysate. That's crazy high!
So the points I hope to have illustrated are that
1. You should avoid simple sugars or simple carbon compounds
2. Less is more. You really do not need to add much.
So choose feeds that are a bit more complex. Cold pressed fish hydrolysate, humic acids, kelp extract, very finely ground oats or alfalfa, crab meal, are all good places to start.
The more finely ground the better. Besides having a "cleaner" tea without chunks of your recipe in it, the higher surface area lets microorganisms access more of it.
Start with small amounts, as little as 1-3 mL per gallon - literally less than 1% by volume. Either test your tea with a microscope, or on your plants, then decide from there how to alter your recipe.
Or you can just copy a very simple recipe I've had success with, which is 3.1 mL of cold pressed fish hydrolysate per gallon and nothing else. Fish hydrolysate is a favorite of mine as it is high in Chitin which helps plants fight insects and diseases such as powdery mildew.
Worm Leachate, Worm Pee, and Vermiwash
A very common misconceptions in vermicomposting is about worm leachate. Worm bin manufacturers who want to sell their product are part to blame, but the liquid coming out of the bottom of a worm bin is not worm pee, nor is it worm tea or extract.
Leachate is fundamentally different from extracts and teas, and it is generally not recommended for direct use on your plants.
Leachate occurs because the organic matter inside a worm bin is so completely waterlogged that it can no longer hold additional moisture. That runoff is coming directly from castings that have "drowned" underwater, cut off from fresh oxygen.
Because leachate forms in stagnant, oxygen-starved pockets, the microorganisms washed out with the liquid are primarily anaerobic - the exact opposite of the aerobic biology you want in your soil and root zones. In these anaerobic conditions, pH can fluctuate, and nutrients can be lost as well.
If you are seeing leachate, or want to learn more about it, you may want to read my post about worm bin moisture.
Vermiwash
Somewhat similar to leachate is "vermiwash."
Vermiwash is created by pouring large amounts of water onto vermicompost, then collecting the water that comes out.
This is a potentially useful idea, but it is not a tea or an extract. The main difference is that Extracts and Teas aggressively push water through the castings or compost, pulling off organisms with it. Vermiwash just passively moves through it, so it collects the "chemistry" side of things like the nutrients and humic acids, but it does not collect the living microbiology.
Quality Assurance on Your Extracts and Teas
The more details you want about the quality of your product means the more effort to test it.
A very simple quality assessment is the brown hue created. A very nice rich brown (refer to the video above) is a sign of quality. Additionally, your extract or tea should not smell bad - besides maybe a slight smell of whatever food you used in your tea.
Note that in addition to looking at your product while being made, you should also look at it after its gone through the sprayer or whatever equipment you're using in case something happened during application and to see its quality as the plants experience it too.
And no, bubbles in your tea has no correlation to the microbial activity - it is simply due to the viscosity of the water because of any feedstocks you may have added.
But for any higher quality of testing beyond that, or for any testing with teas, you'll need to either test it out on live plants by, at the very least, having a control group and a treatment group to compare the differences, or learn how to utilize a microscope to test your teas for quicker feedback. With a microscope you can see whether or not the microorganisms in your liquid are aerobic or anaerobic, and you can even make accurate estimations on their biomass.
Worm Tea & Extract Application Methods
When to Use an Extract or a Tea?
As mentioned earlier, I think extracts are going to be the best option regardless of how you're applying it due to its fool-proof nature and higher microbial diversity. However, it is common understanding that teas are supposed to be more ideal for aboveground plant surfaces, while extracts are best for belowground applications such as root drenches or in furrow treatments.
The thought process with teas is that actively growing microbes immediately produce extracellular polymeric substances to stick to leaves faster, while extracts (supposedly not growing as quickly) don't, and so they will flow deeper into the soil. However, other soil scientists I trust seem to think extracts can do just as well at sticking to leaves than teas. I would suggest experimenting and seeing what your plants have to say about it.
Or, if we're talking about "when" as far as time of day - Research done by Elaine Ingham has showed you can apply an extract or tea at any time of the day. The microorganisms have ways to protect themselves.
Application Rates
I often see people ask "how much extract/tea do I apply?" and it's an impossible to answer question because it is a fundamentally flawed question.
The water is the carrier, the microorganisms are the product. The amount of water you use does not matter at all.
If you're not accounting for the quality of product, you could take a cup of lemonade and pour it into a 50 gallon container and now claim you have another 50 gallons of lemonade. Who cares that its really weak, its still lemonade, right?
It's the same with extracts. The amount of water does not matter, its the amount of the microorganisms.
A better question you should be asking is how many microorganisms should I be applying?
Which I have an answer for! Around 12 micrograms of fungi and bacteria, 900 protozoans, and 9 nematodes per square foot, which is half a million micrograms of fungi and bacteria, 38 million protozoans, and 380,000 nematodes per acre is the bare minimum.
Again, if you're getting serious about this, you really should check out the soil microbiology page.
However, fortunately with compost extracts you can't realistically over apply them. It's the same for teas if you've made them properly, and if the feed ingredient you used wouldn't harm the plant in high amounts.
Fertigation and Drip Lines
I wouldn't suggest running compost teas through drip irrigation tape, fertigation lines, commercial spray rigs, or pivot systems. Teas may contain unconsumed microbial foods, and sticky glues that can form biofilms, clogging emitters and nozzles.
But for extracts, drip lines and fertigation can be a wonderful option. As long as you filter your extract finer than your smallest nozzle or emitter, liquid extracts scale really well across hundreds or thousands of acres.
Pumps, Sprayers and PSI
If you're planning on spraying your microbiology, there are a couple things to consider with your pump mechanics, sprayers, and also PSI of application.
Choosing a Pump
When it comes to selecting a pump for biological extracts, diaphragm pumps are the best way to go for the microbiology's sake. Traditional spray pumps like centrifugal, roller, and piston models are poor choices as their aggressive internal mechanics will chop up delicate fungal hyphae and other micro-fauna.
However, if you or a farm you work with happens to have access to a peristaltic pump, that is another low risk option, and you get bonus points because the same peristaltic motion that moves the water is the same motion that earthworms use to move their bodies! Maybe the microbes will think they're back inside of a worm again?
Choosing a Sprayer
The main consideration which your sprayer is to avoid any sharp angle that the extract or tea might be moving through. If the water has to turn at a 90 degree angle, many of the microorganisms moving at high speed through the sprayer will hit the wall at that turn and die.
PSI
The force that the microorganisms are launched at will not kill them, but the impact when they hit something will. Its like driving a car - driving 60 mph will not hurt you, but hitting something at 60mph will.
40 PSI is considered the maximum safe threshold for direct impact against plant tissue or soil, but if you are spraying a tall tree or something, you can do as much as 80 PSI to reach high places, so long as the droplets are landing softly on those tall tree leaves.
Soil Organic Matter is Critical to Success
You can apply thousands of gallons of high-grade compost extract, but if your soil has no organic matter, those microbes will rapidly die off.
A liquid extract provides the workforce, but Soil Organic Matter provides their housing and food supply. To maximize extract and worm tea performance apply it in soil that has organic matter of at least 3% at the absolute minimum. The biology can build its own organic matter once it establishes, but initially it needs something to get itself started.
Frequently Asked Questions (FAQ)
What Kind of Water Can I use? Is Tap Water Okay?
While using dechlorinated water is always best practice, high-quality worm castings naturally contain high concentrations of bioavailable humic and fulvic acids. These humic compounds rapidly react with and neutralize free chlorine and chloramines upon contact, providing an inherent biological buffer if non treated water isn't immediately available.
Do I need to gas off chlorine before use?
Though ideal, you will be fine as the humic acids in worm castings and compost will neutralize the chlorine.
How much worm castings or compost do I need per gallon of water?
You can really do as much or as little as you want. Because there is no standard of quality, or set point that an extract becomes an extract or tea becomes a tea as opposed to just dirty water, technically your water could be considered extract or tea the moment any worm castings enter it.
But, with that said, 1 pound per 10 gallons is a good starting place.
How much extract or tea should I apply?
This is a fundamentally flawed question. It assumes compost extract has a standardized quality or concentration, which it doesn't. Teas and Extracts can vary wildly in biological density. What actually matters is the microbial biomass applied per square foot of soil.
For example, you could apply 1 gallon of water containing a dense biological payload across 10 square feet, or dilute that exact same payload into 10 gallons of water to cover 100 square feet - the 1 gallon and 10 gallons are both still considered extract, but the total biological delivery to the soil is identical.
Having and using a microscope will give you the details on the microbial quality you need to make a good decision on this, which you can read more about above in this article.
Fortunately, a properly made extract and tea cannot be overdone (unless the feed used for the tea could be bad for plants in high amounts) so if you don't have a microscope just apply as much as you can.
Can liquid compost extract replace synthetic starter fertilizers during seeding?
Yes, liquid extract can absolutely replace synthetic starter fertilizers, but with an important distinction: extract is a biological amendment, not a high-NPK chemical fertilizer. It contains low direct nutritional units, though enough for a germinating seedling's immediate needs.
In real soil, the diverse microbiome in the extract goes to work mining and unlocking bound soil minerals, feeding the seedling naturally. However, if seedlings are planted in a sterile, inert potting mix with zero organic matter or mineral base, the extract has no nutrients to mine and will not provide full nutrition on its own.
Are worm castings inherently better than compost for making extracts and teas?
Not inherently. It always comes back to the microbiome. A masterfully crafted thermal compost can have a far superior biological diversity than a poorly managed, anaerobic worm bin. However, average worm castings are likely to be better than average compost.
Does compost extract help break down organic matter in the soil faster?
Yes. It isn't the water itself doing the work, but the diverse microbiome delivered by the extract. The introduced fungi, actinobacteria, and enzymes accelerate the natural decomposition of leaf litter, crop residues, and organic mulches, cycling those raw materials back into bioavailable plant nutrients.
How do I test if my tea or extract is actually working?
The test most reflective of reality is reality itself. Observing real plant performance over time using the scientific method - setting up an identical control group (untreated) alongside a test group (treated) under exact same conditions - will get you the most accurate results.
Or you can learn to use a microscope to get accurate predictions on how it will react. Be sure to test the liquid as you're making it, but also how it comes out the sprayer or whatever you're using too in case something happens along the way that harms the biology.
How can I evaluate an extract or tea without waiting for plant growth results?
Use a compound microscope at 400x magnification. In less than an hour, a scope gives you direct diagnostic feedback on biological diversity and even oxygen levels.
What specific organisms should I look for under the microscope?
Flagellates, testate and naked amoebae, long fungal hyphae strands, and beneficial non-pathogenic nematodes all indicate aerobic conditions.
High counts of ciliates, rotifers, or swimming anaerobic spindle bacteria (like Lactobacillus species) signal depleted oxygen and potential pathogen conditions.
What is the minimum Dissolved Oxygen (DO) level for brewing tea, and are DO meters reliable?
The absolute minimum threshold for aerobic brewing is 6.0 PPM (mg/L) DO (8.0+ PPM is preferred). However, dissolved oxygen meters can be unreliable in compost teas. Suspended organic solids, proteins, and thick foams coat the sensing probe, leading to false low readings or calibration drift. Checking microbial indicator organisms under a microscope remains the most accurate way to verify real-time oxygen health.
Can a bad batch of compost tea spread human pathogens?
Absolutely. If a tea goes anaerobic due to excessive foods and inadequate aeration, human pathogens like E. coli and Salmonella can multiply rapidly. This is why extracts are safer, and why anyone brewing teas should either verify their brews with a microscope or standardize a proven, tested recipe.
Is the liquid coming out of my worm bin spigot worm tea?
No. That dark liquid is worm leachate which comes from excess water draining out of waterlogged, anaerobic castings. Unlike extract or a properly aerated tea, leachate comes from an oxygen-starved environment and can harbor plant pathogens, volatile anaerobic byproducts, and bad pH levels. It is best to re-process it through dry bedding or a hot compost pile.
Will worm leachate kill my plants?
Probably not, but I still wouldn't use it on plants I intend on eating anytime soon.
How do I stop my worm bin from leaking leachate?
Leachate is a symptom of over-watering or feeding too many high-moisture inputs (like fruit scraps) without balancing them with dry carbon bedding. Stop adding water, reduce high-moisture feedings, and mix dry shredded cardboard or paper into the wet pockets of your bin until the moisture level feels like a wrung-out sponge.
Can you drink worm tea?
You can do whatever you want, but no, drinking worm tea is not recommended.
Theoretically it can be safe, and there are some people who have drank compost tea and reported higher levels of energy (probably because of adrenaline knowing they just drank worm poop water), but I wouldn't ever recommend it.
Can you apply extracts and teas with a drone?
Yes! This is becoming increasingly popular.
Does fish hydrolysate really have to be cold-pressed?
Yes, it does. Hot-processed fish emulsions are cooked at high heat, which denatures the delicate proteins and destroys the complex fats and amino acids that fungi rely on for food. Cold-pressed fish hydrolysate preserves those complex carbon compounds, giving your beneficial fungi the exact high-value food source they need to thrive. If you use heat-treated fish emulsion instead, you're mostly just feeding bacteria.
Do lots of bubbles mean my worm tea is high quality?
No, bubbles are not a sign of microbial quality. Foam and bubbles are simply created by surface tension and the viscosity of the liquid - usually caused by proteins, soluble organic matter, or saponins breaking the surface tension of the water as air pumps through it.
Scott Kent
Owner of Hungry Worms. Worm farmer, soil microbiologist, and educator since 2014. Read more about me here.