Compost tea is a liquid produced by leaching soluble nutrients and extracting bacteria, fungi, protozoa, and nematodes from compost. The tea is made in a brewing process that requires care and the right equipment, just as with making homebrew.

We use compost tea for two main reasons:

  1. To inoculate the soil or foliage of plants with dispersed populations of beneficial microorganisms.
  2. To feed the organisms and the plants with soluble nutrients.

Doing these two things improves the soil structure and ensures that plants are stronger, healthier, grow faster and need less water…

To experience these benefits, it’s critical that you do the whole process of making a compost tea correctly!

First, you’ll have to make or source a high-quality compost that has the desired microbes as these are the organisms you’ll be growing and multiplying in the brewing process. Then you’ll have to make the compost tea brew by following a compost tea recipe – adding the right type of ingredients and closely monitoring the brewing conditions.

When should you apply compost tea?

  1. Any time you notice that the organisms in the soil or on the plants are not at optimum levels.
  2. Seasonally.

In order to combine a number of the beneficial functions that different populations of organisms provide, apply compost tea seasonally.

Not all organisms are active all the time as their activity differs seasonally and daily. In temperate climates, for example, the greatest activity occurs in late spring when temperature and moisture conditions are optimal for growth.

However, certain species of organisms are more active during winter months, dry periods or flooded conditions.

What you’ll need?

Estimated cost: $50 -$200

  1. Compost brewer
  2. Paint strainer bag
  3. Binder clips to bind the bag to a pole
  4. A wooden pole to hang the bag onto
  5. Oxygen indicator strips
  6. Water
  7. Good compost
  8. Humic acid 
  9. Soluble seaweed
  10. Fish hydrolysatefish amino acids or molasses
  11. Oatmeal
  12. Cleaning materials (e.g. hydrogen peroxide (39%), alcohol (90%) or alcohol vinegar)


How to Make and Apply Compost Tea


Estimated time:

  • prepping 1h
  • brewing – 24h
  • application times vary depending on the size of the garden/orchard/food forest.


STEP 0: Acquire the compost

It’s crucial that in this process you have a high-quality compost. 

Which type you’ll need to get hold of depends on the type of system you’re working with. You’ll need fungal-dominated compost for food forests and bacterial-dominated compost for annual gardens.

Note: the nearby forest floor soil is also a good choice if you’re working with food forests.

STEP 1: Choose an appropriate recipe

The amount of compost tea you want to apply to your site depends on the amount of biological activity present in your soil and in the compost from which you are making your tea, but a general recommendation is to apply at least 5 gallons of compost tea per acre, or up to 20 gallons (~ 50 – 190 L/ha).

Compost tea recipes for a 5-gallon (~ 20 l) brewer:

Bacterial-dominated compost tea recipe

  • 1.5 pounds (~ 700 g) of bacterial-dominated compost (e.g. vermicompost)
  • 2 ounces (~ 55 g) of soluble unsulphured blackstrap molasses *
  • 1 ounce (~ 30 g) of soluble seaweed



Balanced compost tea recipe

  • 1.5 pounds (~ 700 g) of balanced compost
  • 1.6 ounce (~ 45 g)  of humic acids
  • 1 ounce (~ 30 g) of soluble seaweed
  • 1 tablespoon of homemade fish hydrolysate **
  • 1 ounce (~ 30 g) of soluble unsulphured blackstrap molasses *



Fungal-dominated compost tea recipe



* The black-strap molasses is great, because it naturally contains a number of beneficial minerals (e.g. potassium) that feed your microbes and soil, but keep in mind that molasses is more of a bacterial meal as bacteria love simple sugars

** Fish hydrolysate is full of nitrogen and fungi love it

STEP 2: Prepare the compost brewer

  • Place your compost brewer (water tank) in a sheltered location with a level surface and access to power and water.
  • Ideally, place it in a space where the water can keep at the same temperature for 24 h without changing due to the day and night temperature difference. Temperature fluctuation within a 24-h period of the brewing process can have an effect on the population growth of various microorganisms. The temperature of the water can vary according to the season, but optimally it won’t fluctuate within 24 h.
  • Fill the tank with the appropriate amount of water.

Note: If you are using tap water, fill the tank the day before in order for the chlorine in the water to evaporate. Also, if you fill the tank in advance the water will have a chance to reach the same ambient temperature.

STEP 3: Plug in the air pump to begin aeration

  • Aerate the water for a couple of hours before putting in the compost.
  • Ideally, the water should be aerated until the concentrations of dissolved oxygen reach 6 ppm. You can test the levels of dissolved oxygen with strips or a special meter.

Note: It’s important that during the brewing process you maintain aerobic conditions (greater than 5.5ppm oxygen). Otherwise, you’ll be producing a compost tea with rather detrimental anaerobic microbes.

STEP 4: Add the compost tea recipe ingredients

  • Add the appropriate amount of humic acid and soluble seaweed to the water and let it brew while you prepare your inoculate.
  • Place the appropriate amount of high-quality compost in the paint strainer bag together with the appropriate amount of oatmeal (if required by the recipe you are using; see above).
  • Place the filled bag into the tank, fastening the bag with binder clips to a wooden pole in order to keep the bag hanging in the middle of the tank.
  • According to the compost tea recipe, add fish hydrolysate and/or molasses to the water.

Note: If you are using your own home-made compost brewer keep in mind that you will need to put one to two air stones, or some other type of oxygen diffuser, into the bag with the compost. 

STEP 5: Brew the compost tea

  • Place the lid on the tank, keeping a small gap for air diffusion, and begin the 24-h brewing process.   
  • At the end of the 24-hour production cycle, continue to aerate the tea while dispensing the liquid into a clean container for application.

    STEP 6: Apply compost tea foliarly or/and to soil

    Foliar application:

    The best time to apply compost tea foliarly is in the morning while the UV radiation is minimal. For the application, you can use any conventional spraying equipment. A typical application rate is 25 gallons per acre (250 liters/hectare) of compost tea concentrate.

    • Take your spraying equipment and fill it halfway with compost tea, then fill to the top with water. (A typical dilution rate is 1:1 = compost tea: water)
    • Spray the whole plant: the stem, the branches, and the leaves.

    Soil application:

    Time of day is less important with soil application because microorganisms won’t be exposed to the sun as much. For the application, you can use a suitable watering can.

    • Take your watering can and fill it with a diluted mixture of compost tea and water, the typical ratio is 5:1.
    • Apply the mixture targeting the base of the plant and the root zone. 

    STEP 7: Clean the equipment

    • Unplug the air pump when the tank is empty and thoroughly clean all parts of the compost brewer, preferably with hot water, after using vinegar, alcohol (90%) or hydrogen peroxide (39%).
    • Leave it to dry so you prevent the creation of small water pockets and anaerobic conditions.
    • If you’re using air stones as an oxygen diffuser, leave them to aerate for another 2-3 hours in the sun so that they dry completely from the inside. This way you can use them again several times.


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