Compost Teas  

Compost Teas for Agriculture

Fields left fallow, heavily ploughed or subjected to large inputs of inorganic fertilisers soon become quite sterile and loose the essential bacteria, fungi, protozoa, nematodes arthropods and mycorrhizal fungi needed to maintain healthy friable soil.

There is no doubt that pesticides and inorganic fertilisers (mineral salts) have greatly increased crop yields, but as they accumulate in the soil resistance to disease increases as soil life decreases and greater inputs of fertiliser and pesticides are needed at ever increasing cost.

DEFRA has recognised the problem and is trying to remedy it.

Sterile soil does not smell “sweet” is no longer friable and needs to be ploughed deeply to aerate and break up solid pans. Healthy, microbially active soil in contrast - converts proteins and carbohydrates leaked as root exudates to plant available nutrient; aggregates the soil to improve water retention and drainage;, produces humus to increase Cation Exchange Capacity and nutrient retention; and improves disease resistance. In short healthy living soil can improve yields while reducing costs.

Ideally soil structure will be rebuilt by adding carbon, slurry and/or green waste compost but this is not always possible and may not provide the microbial diversity needed to get the best yields.

Compost teas are an easy, cost effective way of introducing the micro-organisms that make up a healthy soil food web.

What type of compost tea do my plants need?

As a soil drench.

Brassicas and annual grasses grow in bacterial dominant soils and need a bacterial dominant compost tea brewed for approx 10 hours.

Vegetables and cereal crops and fodder grasses grow in a rootzone with a good mix of fungi and bacteria and need a balanced tea brewed for 18-24 hours.

It is relatively easy to grow bacteria in sufficient numbers but to ensure a fungal dominant tea we recommend that a fungal additive comprising a broad spectrum of fungi be added towards the end of the brewing process. Symbio Fungal Additive

To rapidly degrade stubble add Symbio Stubble Digester to the brewer with a cupful of fish hydrolysate without compost or starters and spray immediately after harvest.


Use the quantities of compost and nutrient on the instructions for the compost and nutrients used. Symbio sell packs suitable for a minimum of 50 litres, 100 litres and 200 litres of compost tea concentrate. Compost tea Starter Packs.

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 standard sprayer, fertigation system (care must be taken to prevent biomass growing on the nozzles) or irrigation system. On spray and fertigation systems the pressure should be below 3 bars or 5 bars with nozzles >2mm.

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.

Frequency of Application

As a soil drench.

Frequency of application depends on climate, crop and time of sowing, , soil organic matter and the other biostimulants and nutrients applied. As a rough guide the following application frequency will provide good results.

Winter wheat and other autumn early winter plantings – Once at sowing , possibly once after 3-4 weeks and once or twice again in spring before growth stops the soil being drenched.

Spring planting - apply 2‐3 times. The first application when drilling seed then at 3-4 week intervals.

For best results ensure that the plants are inoculated with the correct mycorrhizal fungi and apply fulvic and humic acids, and fish hydrolysate as required with each application to feed the micro organisms and use NuGro Liquid Organic fertilisers.

Tank Mixing

You can tank mix compost teas with the following biostimulants.

Symbio Humic Acid, Symbio Fulvic Acid, Symbio HydroAid Yuccah, Symbio Liquid Seaweed, Symbio NuGro Fish Hydrolysate, and NuGro Liquid Organic fertilisers. Always pre dilute 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.
Biostimulants and Liquid Organic Fertilisers

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

Coverage using Symbio Compost Tea and Nutrient Packs

50 litres pack 5,000 –>> 20,000 sq.m
100 litres pack 10,000 –>> 40,000 sq.m
200 litres pack 20,000 –>> 80,000 sq.m

The amount of concentrate required depends upon the general health and organic matter content of the soil. When first applying compost teas we suggest the following as a guide.

Soil organic matter less than 2% -------------- 10 litres concentrate per 1,000 sq.m
Soil organic matter 2% - 3% -------------------10 litres concentrate per 1,000 – 2,000 sq.m
Soil organic matter 3% - 4% ------------------ 10 litres concentrate per 2,000 – 3,000 sq.m
Soil organic matter greater than 4% ----------10 litres concentrate per 3,000 – 4,000 sq.m

There is no maximum amount of water that may be used in the brewer, spray or fertigation tank. You need enough to drench the rootzone - we recommend a minimum of 500 litres per hectare.

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