What is compost extract and how do I make compost extract

Posted by

Adrian

4. November 2026

On 10. August 2026

At the beginning of November, the soil temperature here is below 10°C. This means that microbial activity has already shifted deeper into the soil. For the final plant vitalization of the year, this is the decisive point – and the reason why I no longer brew compost tea for this purpose, but instead produce a compost extract.

The difference in one sentence

Compost tea multiplies microorganisms. Compost extract extracts them without multiplying them.

With tea, the process runs for 24 hours with aeration, heat, and nutrients. With compost extract, water flows through the compost, the organisms detach – and nothing more happens. Everything else follows from this.

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Compost extractShelf life of about one week. The full diversity of the compost is preserved. Any pathogens are not multiplied. However, it lacks the plant-growth-promoting metabolites that only develop during the brewing process.

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Compost teaShelf life of only about four hours. In return, it contains significantly more secondary metabolites, humic acids, amino acids, and plant hormones – the elements that define foliar application.

Why compost extract in autumn

My Johnson-Su compost contains more fungi and spores than I normally find in compost tea. It is precisely these fungi that I want to utilize for the winter.

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Fungi retain nitrogenFungi are slower in mineralization and can store nitrogen more effectively. This is ideal over the winter months: the nitrogen remains bound instead of being leached out.

Then there is the quantity. I prepare the compost extract with 10% compost, whereas a compost tea uses around 3%. The larger quantity simply inoculates the soil more effectively.

Johnson-Su compost with visible fungal hyphae — Johnson-Su compost, two years old. Some of the fungal hyphae have already disappeared – so it is slightly too old.

How I make the compost extract

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The recipeAerated for two hours. Compost to water ratio of 1:10. Without heating, without adding additional nutrients.

This is intentionally simple. I would only need nutrients and heat if I wanted to multiply the organisms – and that is not my goal here.

I supplemented the mixture with half a liter of PhytoGreen Bor. This is a boron ethanolamine and therefore not harmful to the microbiology – unlike borax.

EdaLife V900 brewing system filling a field sprayer — The EdaLife V900 in the morning: compost tea, compost extract, and EM ferments from one machine.

The application

Actually, I had intended to start earlier, but the persistent wet weather thwarted my plans. It was only on this day that the surface had dried sufficiently.

With the small tractor, there were hardly any visible tracks in the wheat field. Driving light and filling the sprayer several times is preferable to me in November than a full load and compacted tramlines.

What we look at beforehand

Under the microscope, we check what is actually in the compost extract: fungal hyphae, spores, testate amoebae. The compost in the image above is two years old, and some of the fungal hyphae have already disappeared. It was therefore already a bit too old.

Fungal hypha in compost extract under the microscope — Fungal hypha in the compost extract, microscopic. This is exactly the structure we want to introduce into the soil in autumn.

This is not a minor detail. A compost extract can only be as good as the compost it comes from – it does not multiply anything that is missing. If you want to know what is actually living in your compost or soil, we can look at that in an analysis.

When compost tea, when compost extract

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Compost teaWhen you are targeting the leaf and seeking a biostimulating effect. Growing season, warm soils, active plants.

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Compost extractWhen you want to inoculate the soil, when it is cold, when you need fungi instead of bacteria – or when you cannot apply the product within four hours.

The compost extract can also be applied directly to the seed or into the seed furrow. And the brewing system does not stand still in winter: EM ferments and hay tea as slurry additives can also be produced with it.

Frequently asked questions about compost extract

What is the difference between compost tea and compost extract?

Compost tea multiplies microorganisms: the process runs for 24 hours with aeration, warmth and food. With compost extract, water flows through the compost and the organisms wash out. It does not multiply them.

How do I make compost extract?

At a ratio of 1:10, that is 10% compost in the water, aerated, without heating and without added food. Two hours is typical. A compost extract can only be as good as the compost it comes from.

How long does compost extract keep?

About a week. Compost tea, by comparison, keeps only about four hours.

When do I use compost extract instead of compost tea?

When you want to inoculate the soil, when it is cold, when you need fungi rather than bacteria, or when you cannot apply the product within four hours. In early November our soil temperature is below 10 °C, so I no longer brew compost tea then.

Why does compost extract make sense in autumn?

The compost contains many fungi and spores. Fungi mineralise more slowly and can store nitrogen better. Over the winter months the nitrogen stays bound instead of being leached out.

Last updated: November 2026. Author: EDAPRO GmbH, Ruswil, Switzerland.