Compost Teas: Microbial Elixirs to Revitalise Your Garden Soil

Compost teas can significantly improve the health of your plants and the quality of your soil. These biologically active solutions are full of beneficial microorganisms, contain readily available nutrients and increase plants’ resistance to disease. In this article, you will learn how to prepare and apply compost teas, and why they are an indispensable part of sustainable gardening.

Compost tea vs worm tea: What is the difference?

Beginners and experienced gardeners alike often confuse compost tea and worm tea. At first glance, these two types of organic solutions have much in common. Both worm tea and compost tea are produced as a by-product of composting, and both are associated with ecological gardening and sustainable agriculture. So what are the differences between worm tea and compost tea?

Compost tea

Compost tea is a liquid produced by extracting beneficial microorganisms (bacteria, fungi, nematodes and others) from compost using a brewing process. True compost tea contains all the organisms and soluble nutrients that were present in the compost before steeping. Depending on the preparation method, there are two types of compost tea – non-aerated and aerated.

• Aerated compost teas (ACT) are produced with a constant supply of oxygen to the water, which supports the growth of beneficial aerobic bacteria.
• Non-aerated compost teas are made by simply soaking compost in water for a certain period without additional aeration.

Worm tea

Worm tea is a liquid that drains to the bottom of home vermicomposters. Although this leachate is rich in nutrients, it differs significantly in composition compared with compost tea. The content and balance of nutrients and microorganisms in vermicomposter water are greatly influenced by the materials the worms feed on and the conditions inside. Worm tea can be useful, but it often contains more pathogens than properly prepared compost tea.

Benefits of compost tea

Compost teas are useful for both outdoor gardeners and indoor growers. They naturally support plant growth and improve overall plant health, vitality and nutrient uptake. Compost teas also improve soil structure by increasing microbial activity, which leads to faster decomposition of organic matter and the release of nutrients in the growing medium. In addition, beneficial microorganisms help plants defend themselves more effectively against harmful pathogens.  Thanks to their easy preparation, application and low cost, compost teas are an ecological alternative to chemical fertilisers and pesticides, making them an excellent choice for growers practising sustainable gardening methods.

• Source of nutrients – During the steeping process, important nutrients and minerals are released from the compost and become immediately available to plants when applied to the soil or sprayed on the leaves. This means you can use compost teas as a universal natural fertiliser with a fast effect.
• Microbial life – One of the main advantages of compost teas is that they are literally full of beneficial bacteria, fungi, nematodes and other microbes. These microorganisms play a key role in the soil and food chain. Their main task is to break down organic matter into nutrients for plants.
• Disease suppression – Scientific studies have shown that compost tea can be effective in suppressing fungal and bacterial diseases that threaten plant health, and it can be used as an alternative to chemical treatment.
• Improved soil quality – Regular application of compost tea improves soil structure and its retention properties, namely aeration and the ability to retain water and nutrients. As a result, compost tea loosens clay soils and helps sandy soils retain water and nutrients better.

How to prepare compost tea

You can prepare your own compost tea either from powder for preparing compost tea, worm humus or from your own compost. In the latter case, however, make sure it is well matured compost that does not contain any pathogen spores. Compost tea can be made with or without aeration, and you can add supplementary nutrients with a high sugar content, such as molasses, which will serve as food for microbes. For the best results, we recommend choosing the aerated method, but the most important prerequisite for success is quality compost.

You will also need:

• Non-chlorinated or standing water – The effect of compost tea depends on a thriving population of beneficial microbes. Chlorine and chloramine not only destroy harmful pathogens in drinking water, but also harm these microorganisms. While chlorine is relatively unstable and gradually evaporates from the water, chloramine must be neutralised using a carbon filter. If you are sure that your tap water contains only chlorine, leave it to stand for 1-5 days in a dark, cool place. You can speed up the process by aerating it with an air stone for 12-24 hours or by boiling the water.
• Container with an aeration system – For preparing compost tea for small or medium-sized gardens, a 10-20 litre bucket is suitable. A simple and effective aeration system can easily be assembled from an air pump, an air stone and several flexible tubes.
• Microbial food – Adding molasses or liquid preparation for compost tea will speed up the multiplication of beneficial microbes in the mixture being prepared. Use supplementary sugars in reasonable amounts to prevent imbalance and the proliferation of anaerobic bacteria in the tea.

Step-by-step guide to preparing compost tea

• Preparing the compost: Start with quality, well-matured compost or a loose mix for preparing compost tea.
• Mixing and soaking: Fill the container with water and add compost at a ratio of approximately 1 part compost to 5 parts water, or according to the instructions.
• Aeration: Leave the mixture to steep for 24-48 hours, aerating it throughout and stirring it several times.
• Straining and storage: After steeping, strain the mixture and use it immediately if possible, because at this point the tea contains the highest number of beneficial microbes.

Using compost tea

You can apply compost tea directly to the roots of plants or as a foliar spray; each of these methods has its advantages.

• Applying compost tea to plant roots: Simply pour fresh compost tea into the soil near the plant’s main stem. This method enriches the soil and delivers beneficial microorganisms and nutrients directly to the roots. Water plants with compost tea every two weeks throughout the growing season.
• Compost tea as a foliar spray: You can spray compost tea directly onto plant leaves, which provides an immediate effect in the fight against pathogens. Apply the spray early in the morning or in the afternoon to avoid scorching the lea