Compost tea is water in which compost has been soaked and then strained. It is an effective, low-strength, natural fertiliser for vegetables, seedlings and garden plants, and it can suppress fungal plant diseases. The tea-brewing process extracts, and in some cases grows and multiplies nutrients and beneficial bacteria and fungi from compost and suspends them in water in a form that makes them quickly available to plants.
The three main plant nutrients ~ phosphorous, potassium, and nitrogen ~ are used up in large quantities in vegetable gardens. Due to the effects of close planting, the major elements may be in short supply, so it is often necessary to give the growing vegetables a fertiliser boost.
Compost tea contains all the water-soluble nutrients from your compost. This means that the richer your compost is, the more nutritious your tea will be. The nutrients will naturally be more diluted than in straight compost.
Probably the greatest advantage of using compost tea lies in the fact that the micro-organisms that live in your compost ~ beneficial fungi, bacteria, nematodes and protozoa ~ will multiply in a compost tea. Microorganisms are what keep soils alive. A small particle of soil can contain thousands of different species of microbes. They break down organic matter, recycle nutrients, maintain soil structure, promote plant growth and control pests.
When you apply the high numbers of microbes typically found in compost tea, it will help the local plants and ecosystem literally from the ground up.
Another advantage is that there’s increasing evidence that plant diseases can be suppressed by treating plants with compost teas. This is most likely due to the enhanced microbial populations. They support plant health and stronger plants are less disease-prone. Also, the beneficial microorganisms can out-compete and inhibit the harmful species both above and below ground.
Compost tea is also thought to control insects such as spider mites.
Water-soluble homemade fertilisers are short-acting but should be applied no more than every two weeks, usually as a thorough soaking.
There is a surprising amount of controversy about compost tea, with some passionately praising it and others saying it makes no difference to their plants. We’ll let you be the judge.