Homemade Liquid Fertilizer from Compost Tea - How is Compost Tea just BS - Kesser and Steen have heard that you just throw weeds from your organic vegetable garden into a big bucket and wait .. that's how you brew self-fermented compost tea - but there are many ways to make compost tea, almost like every housewife has her own way of cooking rice .. That's why they seek some advice from Professor Hendricks, their teacher in the Nature and Innovation class. Compost tea or extract is in its simplest form a kind of soup, where you put plants, especially weeds, in water and let it steep for some time. The idea is that the soluble nutrients and some microorganisms from the plant material are released into the water, which can then be used as fertilizer.
Kesser and Steen are apparently not completely wrong, because what they have heard about is actually quite a useful method, especially when thinking in the direction of permaculture, where you want to work with the resources you have at hand. If you just put it in a bucket of water and leave it there, a slow, oxygen-poor decomposition takes place – a bit like silent fermentation or putrefaction, depending on how it develops. It may smell a little, but that doesn’t necessarily mean it’s bad. Some plants like nettles, dandelions, collard greens and other strong greens contain a lot of minerals, and it’s these that you’re trying to extract. Some people choose to strain the liquid after a week or two and use it as a liquid fertilizer, either diluted or as is, depending on how strong it is.
During fermentation, microorganisms break down the cells in the plant material. This results in the formation of short-chain organic acids, such as acetic acid, lactic acid and butyric acid. These acids can have several functions: they lower the pH, which can inhibit harmful microorganisms, and they can also make certain minerals more soluble and thus easier for the plants to absorb. If the fermentation has been active with lactic acid bacteria (e.g. from a Bokashi-like process), compounds can be formed in which nutrients — such as calcium, magnesium or potassium — are temporarily bound to organic acids or even small peptides or amino acids.
What Kesser and Steen propose with transport via amino acid complexes is entirely realistic. It is known that plants can absorb certain nutrients more efficiently when they are bound to organic molecules such as glycine or glutamic acid. This is partly because such complexes can pass through cell membranes more easily, and partly because they are not so easily bound to the soil, where they would otherwise become inaccessible. When spraying or watering with such an herbal soup, some of these complexes can potentially penetrate through the plant's leaf openings or be absorbed through the roots, especially if the solution is diluted and not too acidic.
At the same time, there will be microbial metabolites in the liquid that can function as growth stimulants — for example enzymes, vitamins and signaling substances. These compounds can affect the plant's own physiology, for example by stimulating root growth, improving stress response or changing the microbial balance around the roots.
Even if the NPK number in the traditional sense is low, the value lies in the bioavailability, in the living dynamics and in what one could call “biological synergy” — that is, how plants, microbes and organic compounds work together. As long as you keep an eye on the pH and do not overfertilize (for example, avoid pouring oxygen-poor, strong-smelling liquid directly on delicate plants), it is both a sustainable and creative addition to the garden, which can yield good results - so you get first and foremost a liquid that is rich in dissolved organic compounds and microbially processed nutrients, rather than pure NPK fertilizer in the classic sense.
When you make a liquid ‘chop and drop’ – This applies not only to N-P-K, but also calcium, magnesium, sulfur, iron and trace elements, such as manganese, copper and zinc. Many weed plants have deep roots and are very good at retrieving precisely those elements from layers that cultivated plants rarely reach. Nettle is a good example – it is rich in nitrogen and iron. Others also have a lot of potassium. But exactly how much NPK ends up in the extract is difficult to say without laboratory analysis. These are typically very weak concentrations compared to synthetic fertilizers – but that is not the point either.
Kesser and Steen see it as more than just fertilizer. For plants, it is not just about getting nutrients, but about creating connections – and they do it to get something in exchange: for example minerals, protection or access to water. If you add extracts from other plants that have done the hard work themselves, you can stimulate the same symbioses.
