Compost Teas  

Compost Teas for Horticulture and Landscape

The soils, rootzones and potting mixes used in the growth of vegetables, garden plants and trees are fairly sterile for a variety of reasons.

Compost Teas for Horticulture and Landscape

Peat based growing media, even when mixed with green waste compost, is by its very nature low in microbial activity. Soils left fallow for several months loose the nutrients from the plants that support a healthy mix of bacteria, fungi, protozoa, nematodes and arthropods essential for nutrient recycling, disease suppression and soil friability, while landscape contractors often have to cope with heavy sub soils or heavily compromised top soil.

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, perennial garden plants and perennial grasses grow in a rootzone with a good mix of fungi and bacteria and need a balanced tea brewed for 18-24 hours.

Shrubs need a more fungal dominant tea while hardwood trees and conifers grow in soils rich in fungi need a very fungal dominant tea brewed for 24-36 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. 

When growing plants or trees in sterile growing media or disturbed landscape soils, Symbio Liquid Mycorrhizal fungi may be added to the first application of tea if the tea is certain to come into contact with the roots. 

As a Foliar Spray

There is anecdotal evidence to suggest that a bacterial dominant tea applied as a foliar spray may help the plant combat disease and drought stress. This can only be ascertained for a given set of circumstances on a trial and error basis. The tea should be brewed for 8-­‐10 hours and a bacterial additive containing a broad spectrum of beneficial bacteria may be added.


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 and 100 litres of compost tea concentrate. 

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), irrigation system or simple watering can. On spray and fertigation systems the pressure should be below 3 bars.

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

Frequency of application depends on climate, glass house or field grown plants, general soil composition and health, the plants being grown, soil organic matter and the other biostimulants and nutrients applied. As a rough guide the following application frequency will provide good results.

Landscaping ‐ new trees and shrubs, bedding plants and roses, bulbs, grass. Once at transplanting planting and once a few weeks later. If possible further applications will usually enhance plant growth.

Field grown plants, shrubs, and trees – Once at transplanting planting or seeding, then monthly until harvest or growth is established in the first year. In poor quality soils in subsequent years an application in spring and autumn will assist root and top growth.

Field grown flowers and vegetables
– Once at planting and after 2-3 weeks then every 4-8 weeks until harvest.

Glass house plants and containerised trees
– Every 4-6 weeks from cutting or sowing and also when transplanting to larger containers.

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 BioBooster 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 BioBooster Fish Hydrolysate, and BioBooster 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. 

You can also add Symbio 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

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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