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Liquid Microbials –  What are they?

In this Guide (click to jump to section):

There are many types of liquid microbials, most notably compost extract activated compost extract, and compost tea. These kinds of liquid composts are used to apply microbes in a way we cannot achieve with compost in its solid form. Compost in a solid form is used to apply to the surface of a soil and helps to increase organic matter. In a liquid form, we can introduce microbes in a compost into the depths of the soil, around the roots where the plants need them, general soil treatments below the surface of the soil, as well as onto plant surfaces. Liquid microbials are also optimal because they can be spread over large areas very easily, whereas most people do not have the amount of compost required to spread as a top dressing over their entire farm. 


Essentially, what they are: microbes found in a compost have been shaken in water, so that they fall off the organic matter particles of the compost and into the water. The result is a liquid that is rich in microorganisms, humates and fulvics. This liquid can be used to reintroduce microbes into your soils, around root systems and onto your plants.

The quality of your compost will determine the quality of your liquid inoculum. Even with the best equipment, it is not possible to extract what is not present in the compost to begin with. (This is what we mean when we say that we sell our compost for inoculum and is also why we make it known that our compost is ecologically complete, as we have a very high density of all the organisms required to regenerate soils and plant microbiomes in our product).



The difference between compost extract, activated extract and compost tea


Compost extract is simply microbes shaken off the organic matter of compost and into water. Ba da boom, ba da bing! 


Activated extract means that the compost was fed certain foods 3-7 days before the extraction was made, activating the microbes in the compost. It’s similar to pre activating a sourdough culture before making a loaf of bread. The foods are metabolized by the microbes in that time frame, and then an extract is made with that activated compost. 


Compost tea begins as a compost extract, after which microbial foods are added into the water, microbes are activated and multiplied in the water with an air bubbler for 24 to 48 hrs. 


The equipment needs for extracts/activated extracts vs compost teas are different. 


Compost teas work great when made well. However,  they can go wrong very quickly by over feeding the microbes in the water, if your water is too warm or if it is too hot outside. Compost tea can turn bad very quickly as well. 


A person on site trained in microscopy is required for the responsible use of compost tea. If a person is sure their compost is good and ecologically complete, then no microscopy is required when making compost extracts. We just want to make sure we have a dense enough colour to the liquid, which is something we can verify with our eyes. 


The reality Docterre works in, in an agriculture and municipal context, the time to make compost tea is just not realistic for most businesses and municipalities who require large volumes of liquid microbials. 


The other truth Docterre has discovered over the years is that, when the composts are very high quality and are active, compost extracts and activated extracts work just as well as compost teas, even for foliar sprays. 


Most of the farms we work with are making compost extract or activated extracts with results just as good as if they were making compost teas. They are saving money and time as well because of this. Most farms and municipalities we work with are using Docterre’s compost as well, as we guarantee top quality product and the densest and most diverse presence of microbes available on the compost market. 

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Comparison Table

Liquid Inoculum Comparison Table?




Level of

difficulty to make

Image by Manikandan Annamalai




Activated Compost



Compost Tea



of time to make

Image by Ocean Ng

5 minutes to 1 hour

5 minutes to 1 hour


Do we Feed the Microbes to Make

Image by ThisisEngineering RAEng


Fed 3-7 days before extraction

Fed after extraction, in the water



Very Stable

Microscopy  required







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What is an appropriate compost to water ratio when making extracts or teas?


When using Docterre’s compost, the ratios are as follows:


  • For larger batches:
    For every 1000L of water, use 30-40 L of compost (1 ½ to 2 buckets)


  • For smaller batches:
    For every 20L (bucket) of water, use 3 cups of compost 


The amount of compost needed is determined by the quality of the compost.

Compost Extract

How To Make Compost Extract

Activated Extract

The extract is simple and quick to make.


To make an extract, enough energy must be applied to the organic matter to detach the microbes. We must keep in mind that microbes are fragile beings so we use a gentle form of energy.


For this reason, small quantities of compost extract are made by hand. 


  • You simply put the compost in a compost mesh bag that will serve as a filter. Immerse the bag in non chlorinated water and massage it to extract the microbes off the compost, and into the water. The process takes about 3 minutes for a 20 liter batch. 


For larger quantities, air is often used as a form of energy to shake up the microbes off the compost and into the water. The bag must have 400 micron holes to allow the largest microorganisms to pass while keeping the majority of the organic matter. 


We are looking to achieve a density of color of a dark chocolate liquid. Once this is achieved, your extraction process is done. 


Since the microbes are not multiplying there is no creation of biofilm difficult to clean. 


The extract is ready to be used to reintroduce life into the soil. 


Activated Extract


The activated extract is made in the same way as compost extract, except with one more step before the extraction process. The step is to activate the microbes with food, this wakes them up, so the microbes are nice and active by the time you get to the extraction process. Basically, 3 to 7 days before doing the extraction, we make sure of the humidity level of the compost and we add activation powders or other microbial foods to the compost. We then avoid disturbing them for the next few days. 


Please see our detailed pre-activation instructions HERE

Please see the reasons for which you would activate your compost HERE. 



You will need the equipment to make your compost extract/activated extract and the equipment to apply them. 


The principle of extraction consists in putting enough energy on the organic matter to detach the microbes there. Since we work with the living, this energy must be relatively soft in order to avoid killing microbes. We can therefore use water to wash the compost or put the compost in water and inject air into the compost to dislodge the microorganisms.


Then the liquid must be filtered to pass into your sprinkler system. We recommend a filtration of 400 microns to allow the largest organisms to pass. This is the minimum size to allow the biggest microbes to get out.


A good extractor system will have the air blowing directly in contact with the compost as the water passes through or is in contact with the compost. 


Docterre can help you find the extraction system you need or support you in the design of your extractor. We can also manufacture custom extraction bags. See our Equipment services page for more information or to book an appointment for our more advice. 


For more information about compost extracts or activated extracts, how to make them, how to use them etc, please book a general consultation with us.

Compost Tea
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How To Make Compost Tea

Making tea is a bit more complicated than an extract. Compost tea begins by making a compost extract. From there, additional steps are taken to turn the extract into a compost tea:


  1. In your compost tea brewer, make your compost extract

  2. Remove the compost mesh bag from the brewer

  3. Turn on your air pump

  4. Add in your microbial foods into the compost extract: 
    - 0.001% of your total volume of water is the maximum amount of foods you can add into a compost tea, unless you are in very cold conditions (in which case you can put 0.002% foods)
    - You can use an activation powder as microbial foods
    - You can use other microbial foods, such as liquid kelp or fish hydrolysate


  5. Let this brew for 24 hrs if your water is between 10 and 20 degrees, and 48 hrs if your water is colder. You’re done. 

  6. Use within 4 hours of finishing your brew cycle

Oxygen levels must be maintained high enough to prevent the multiplication of harmful organisms. The brewing time varies mainly according to the temperature of the liquid, which is between 24 and 48 hours. The hotter it is, the shorter the brewing time, and the colder it is, the longer it will be. If it is too hot outside, past 23 degrees, we do not recommend using compost teas. 


You will need an air pump that produces a minimum of 0.05 cfm (cubic feet per minute) per gallon of liquid.


  • 5 Gallon Brewer: 500 GPH - 1000 GPH

  • 15 Gallon Brewer: 1000 GPH - 1500 GPH

  • 30 Gallon Brewer: 1250 GPH - 1500 GPH

  • 50 Gallon Brewer: 1250 GPH - 2000 GPH

It is said that the big advantage of tea comes from the creation of a biofilm by the microorganisms during their multiplication. This biofilm is like a glue and allows them to stick to the surface of the plants. Tea is therefore used as a foliar treatment to inoculate the aerial parts of plants. This treatment allows the microbes to fight and occupy the space occupied by the pathogens. So the difference between the extract and the tea is that the tea treats the leaves. 


It is true that compost teas will do all this. However, a compost extract or activated extract made with high quality active compost will also have microbes with active biofilms, and will be able to stick to plant surfaces. 


If your goal is to add microbes to surfaces as well as feed them, this is where adding in extra microbial foods in the spray mix is worth your while. 



First, during the whole tea making process, the temperature and oxygen parameters must be well controlled to avoid the multiplication of pathogens. There is therefore a risk of escaping the recipe and missing the batch.


Secondly, the necessary food for the microbes is also an important factor. Too many ingredients or a bad recipe can promote undesired microbial growth. Tea is much more complicated to manage once the process is complete because it must be used quickly. It also requires better planning for manufacturing since it takes 24 to 48 hrs to manufacture.


Finally, the cleaning of the equipment is much more complicated since during the multiplication of microbes there is creation of biofilm. It is very important to keep in mind that these are biological processes such as the production of beer, yogurt… so the cleanliness of the equipment can be a factor of failure or success.


Making compost tea requires more than a compost mesh bag and an air pump to make the extract. As with a good extractor, the extraction needs for the air to blow through the compost as the water is passing through or as the water is in contact with the compost. A good compost tea brewer also requires aeration during the entire brewing process. This aeration must come from the bottom of the compost tea brewer, and must create a rumbling boil on the surface of the water. 


For additional help with regards to equipment needs, please book an equipment consultation with us. 

Dosage & Application

Liquid Microbial DOSAGE


Typical liquid microbial treatments are as follows.


The minimum treatment per acre is 15 gallons (56 liters), although most people set their minimum at 30 gallons (115 liters) per acre. Per hectare this is equivalent to 130 to 300 liters per hectare.


Liquid Microbial APPLICATIONS

Early spring, late spring and early summer treatments focus on plant, root and leaf treatments. From July, the treatments target the soil around the root system, around the drip line of the plants.


In the fall, treatments can be made by sowing cover crops for annual production.


For perennial crops, once the plants go dormant, it is recommended to perform both a generous foliar and soil treatment.


Generally, whenever we already have a pass, we can double this function with an application of microbes.


When soil ecosystems are not yet fully healthy, it is advisable to use the product every 10 days.


Other consistent application methods apply treatment at each new growth stage of the plant. For perennial fruits, the last foliar application should be at the fruit set and the remainder should be directed to the soil until the plant is dormant in the fall.


The product can be used 48 to 72 hours before a type of weather event that can lead to infections and pest outbreaks.


For more information on the use of this product, please book a general consultation and/or register for our Living Soils for Farmers course.

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