Coffee is the second most consumed beverage after water. The coffee grounds usually end up in household waste or on the compost heap. However, it can also be used directly as fertilizer for garden plants.
Coffee grounds are often underestimated as a natural fertilizer, because they contain a comparatively high amount of nitrogen, for a purely plant-based starting product. The nitrogen, sulfur and phosphorus-rich protein content of raw coffee beans is a considerable eleven percent. Although the roasting process completely decomposes the plant protein, as it is not heat-stable, the plant nutrients mentioned above are largely preserved in the decomposition products. During the subsequent roasting process, only a small proportion of the plant nutrients is flushed out. In addition, humic acids are formed during roasting, which is why coffee grounds have a slightly acidic pH, unlike freshly harvested coffee beans.
How to fertilize plants with coffee grounds?
If you want to use your coffee grounds as fertilizer, you should first collect them, because it is hardly worth going out into the garden with every single used filter bag and scattering the remains around the plants. Instead, collect the coffee grounds in an airy, dry place in a bucket. It’s best to hang a fine-mesh strainer in it, where the fresh coffee grounds can dry quickly so they don’t start to mold.
If you have collected a large amount, sprinkle a few handfuls of the dry powder around the root area of each plant. Coffee grounds have a mild soil acidifying effect and also enrich the soil with humus. Therefore, it is best suited for fertilizing plants that prefer acidic humus soil. These include hydrangeas, rhododendrons and blueberries. It is important to work the coffee grounds flat into the soil or cover them with some mulch. If they are simply left on the surface of the soil, they decompose very slowly and their fertilizing effect is hardly noticeable.
For flowers on balconies and other potted plants, you can mix a few handfuls of coffee grounds into the new potting soil before repotting to enrich it with additional nutrients and trace elements.
Compost coffee grounds
You can also indirectly use your coffee grounds as fertilizer for the garden by first composting them. Simply spread the moist powder on the surface of your compost pile. You can compost the filter bag as well, but you should pour out the coffee grounds first, otherwise they will easily start to mold.
Cold coffee instead of coffee grounds as fertilizer for house plants
You should not use coffee grounds as fertilizer for indoor plants, because the powder hardly decomposes on the pot ball and sooner or later starts to mold. However, cold black coffee from the pot is suitable as a free fertilizer. Simply dilute it with water in a 1:1 ratio and use it to water your houseplants, potted plants and balcony flowers. It should be dosed very sparingly, especially for house plants. Do not use more than half a cup of diluted coffee per plant per week, otherwise there is a risk that the pot ball will become too acidic and the house plants will not grow properly.
Coffee as a natural pesticide
A few years ago, Nature magazine reported that a two-percent caffeine solution had been successfully used in Hawaii to control slugs and snails. After the initial wave of euphoria had subsided, disillusionment quickly spread among hobby gardeners: After all, it takes almost 200 grams of powder to make one cup of the highly concentrated anti-slug coffee, which is very expensive. Moreover, although the caffeine is an organic pesticide, it is nevertheless a highly toxic one. It is also likely to kill numerous other creatures in such high concentrations.
However, a normal-strength coffee diluted 1:1 with water works well against fungus gnats on indoor plants, because the caffeine it contains is toxic to the larvae living in the pot’s root ball. In addition, you can use the coffee solution with an atomizer well to control aphids.
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- Angel trumpet