In the gardening environment, the term “tea” is used for many different kinds of brews, such as manure tea, comfrey tea and stinging nettle tea.
These kinds of teas are usually simple extracts of nutrients and other organic substances. Sometimes they are allowed to ferment for a few days and then also become a source of fermenting microbes.
Compost tea, however, is deliberately brewed for a specific purpose - to extract and further multiply the microbes present in a small amount of compost. Therefore it is very important to use only high quality mature compost!
Anaerobic, foul smelling “compost” contains the wrong kinds of microbes that can actually kill your plants or negatively impact soil biodiversity.
To make compost tea, a few handfuls of compost are added to a special compost tea brewer filled with non-chlorinated water, together with small amounts of microbe food such as unsulfured molasses, rock dust, kelp meal and sea minerals. Finally, a constant stream of air is injected into the brewer to ensure a sufficient oxygen supply to the microbes. After a couple of days the surface of the brew will be frothy and the tea is ready to be used immediately.
Where compost is in short supply, compost tea is a great alternative for inoculating the soil with microbes. Additionally, the tea can be sprayed onto plant leaf surfaces, helping to protect plants from plant-feeding microbes.
Compost tea is neither a fertilizer nor a pesticide, but a microbial inoculant designed to increase biodiversity in the soil and on plant surfaces. Just as it is important to start with high quality compost, it is equally important to keep the brew well aerated.
Compost tea brewers are specially designed to minimize anaerobic pockets, where the wrong kinds of microbes can multiply. As an added measure of caution one can add a few tablespoons of beneficial fermenting microbes, which generally out-compete the pathogens in low oxygen environments.
Finally, it is important to use the finished compost tea immediately, as the brew becomes anaerobic within hours.
Commercial compost tea brewers can be pricey, but many home gardeners report great success with a simple homemade brewer made from a five gallon bucket, an aquarium pump and air tubing.
Organic gardening does not rely on products and compost tea is no exception. It is useful under some circumstances, but certainly not necessary.
We go much deeper into this topic in our online course, which you can discover here: