Compost Teas  

How to make good Compost Tea

Compost Tea is not a product but a solution to transport micro-organisms. Compost tea is a temporary survival unit that allows living micro-organisms to be taken from the compost, multiplied rapidly and introduced to the soil and leaf.

What is Compost Tea?

Compost tea is a liquid extract of compost containing.

• Enzymes and amino‐acids
• Bacteria, fungi, protozoa and beneficial nematodes
• Water soluble nutrients and organically bound nutrients

The quantity, diversity and quality of these micro‐organisms depends on the quality of the compost used for the extraction, the brewer used and micronutrients and starters added for optimum organism growth. It can be either bacterial or fungal dominated.

How to make compost tea brews

There are three essential ingredients

A compost tea brewer or Xtractor –Which is a specially designed container and an air supply that keeps the oxygen level at at least 6ppm all the time. It is very important to keep the brewer clean so choose a brewer that does not have internal pipes, nooks, corners and crevices which harbor biofilm and are difficult to clean. You should not allow a brown film to build up on the surface of the brewer; this may contain harmful microbes that reduce the potency of the compost tea you make. 

Good compost – Ideally you should buy pre tested compost made by a reputable supplier that is pathogen free and contains and broad spectrum of the beneficial bacteria, fungi, protozoa and nematodes needed to make a good compost tea. If you make your own compost it should have at least 50% woody material in the mix and be made aerobically. It should be turned when the temperature reaches 65oC and typically be made in six – eight weeks. You may then have to leave the compost for a month or more or inoculate it with a fungal inoculant to allow time for fungi to grow.

The correct nutrients – You need to add foods to feed the bacteria and fungi so that they can grow when they have been extracted from the compost. Different foods feed bacteria and fungi. Bacterial dominant teas are made with black strap sulphur free molasses or sugars while fungal dominant teas are made by adding fish hydrolysate and humic substances so be sure to use the correct nutrients for your brew.

Each batch you make will be different depending upon the ambient temperature, pH of the water used, brewing time, compost quality and nutrients added. It is best to make tea at the ambient temperature so you grow the microbes that will survive in the soil temperature to which they are applied

Step 1 - Fill the brewer with the desired amount of water. If using chlorinated water run the air pump for an hour or two to release any chlorine in the water.

Step 2 - Add the nutrients to the water.

Step 3 - Add the compost to the basket or for smaller brewers into the water.

Step 4 - Brew for the required time.

Step 5 - Switch off the brewer and allow the compost tea to settle for 20-30 minutes.

Step 6 - Decant the compost tea via and extra filter if necessary to your spray tank or irrigation tank and apply as a soil or foliar drench.

Step 7 - Thoroughly clean the brewer.


If the compost tea foams you can add a small amount e.g. half cup of cooking oil. The finished compost tea should be sprayed within 4-5 hours before the microbes use up all the oxygen and it goes anaerobic. If you cannot apply the tea for any reason, simple run the aerator for a few minutes every hour until the tea is applied. If applying bacterial or fungal additives follow the instructions on the pack as a general rule bacterial additives are added at the start of the brew cycle and fungal additives at the end of the cycle.

Brewing times
You can further refine the type of tea you make by altering the nutrients and brewing time.

With an ambient temperature of between 15-20oC you can make the following brews.

Bacterial dominant
Use more molasses and brew for about 10 hours in a brewer.

Fungal dominant
Use humic substances and fish hydrolysate and brew for 18-24 hours because fungi take longer to develop

Protozoan dominant
Brew for 48 hours to give the protozoa time to start eating the bacteria and increasing in number

If the ambient temperature is cooler increase the brewing times they may be doubled if the ambient temperature is 6-8oC

If applying the compost tea in a temperature controlled glasshouse make the tea in the glasshouse.

When using an Xtractor brewing times are shorter read the specific instructions for the Xtractor.


If you develop your own brewer and compost you should have the compost and resulting tea analysed to make sure it has the correct ratios of bacteria fungi protozoa and nematodes. It is also a good idea to have your soil analysed for its biology so that you can make a compost tea that solves your problems. Symbio can test soils, compost and compost teas for bacteria, fungi, protozoa and nematodes. Read more


Compost teas should not be mixed with inorganic chemicals or fertilisers and if the spray tank has been used for pesticides it should be thoroughly cleaned before filling with compost tea. Compost teas can be applied via sprayer, fertigation system (care must be taken to prevent biomass growing on the nozzles), irrigation system or simple watering can.

Add the compost tea to the spray tank and dilute with de chlorinated water. If mains water is used add it to the tank the day before to give chlorine time to dissipate before adding the compost tea.

Tank Mixing

You can tank mix compost teas with the following biostimulants.

Humic acid, fulvic acid, yuccah, molasses and sugars, liquid seaweed, fish hydrolysate, and liquid organic fertilisers. Always predilute the biostimulant with at least an equal amount of water and add it to the nearly full spray tank after diluting the compost tea in the tank.

You can also add liquid mycorrhizal spores and propagules if using the tea as a soil and root drench. 

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