There are many ways to reuse coffee grounds. One of the most sustainable is undoubtedly to use coffee as fertiliser for plants. Users who consider recycling this way always come to the first question: is coffee good for plants? What are the advantages of using coffee as a plant fertiliser?.
Is coffee good for plants?
The use of coffee grounds to fertilise plants is as old as coffee itself, as it is a natural element that can be mixed with the nutrients in the soil. Its properties are effectively transferred to the soil and the plants we grow in it benefit from these properties. But it all depends on the type of plant and the condition of the coffee.
Coffee for fertilising plants can be used in four main ways:
- Ground coffee. We add the coffee without having used it before.
- Coffee grounds. Once the coffee has been used, add the grounds to the soil.
- Liquid coffee. We would prepare coffee as if we were going to drink it ourselves and pour it into the soil.
- Manual mixing of coffee with compost. When we prepare our own substrates, ground coffee (used or not) would be a part of it.
Advantages of coffee fertilizer for plants
Coffee for fertilising plants has the following proven benefits for an organic garden or potting soil:
- It is suitable for earthworms, but always in small quantities. Remember that earthworms are very important for good soil, so the last thing we want is to kill them.
- It is terrible for snails, slugs and other invertebrates that can eat your plants.
- The natural nutrients and minerals in coffee enrich the soil when mixed with it, mainly nitrogen, an essential element for growth.
Related: Worms in coffee makers. Myth or reality?
Ground coffee for plants (unused)
Ground coffee as a plant fertiliser is an ideal solution because it contains all the beneficial properties of coffee for plants, as we have just seen. Moreover, it is very easy to disperse because it is ground without creating lumps or thick layers.
The only problem is its price, so it is not commonly added to commercial substrates. Coffee is designed and manufactured for human consumption due to its high price. Therefore, it is more practical and sustainable to use coffee grounds as fertilisers for your plants.
Coffee grounds for plants (used)
The essential difference between ground coffee and coffee grounds is that the latter has already been infused. The advantages of using coffee for plants are mainly two: nitrogen and minerals. Coffee grounds for plants have up to 10% nitrogen in their composition, which is essential for plant growth.
Using coffee grounds is simple: add the coffee grounds around the plants, always keeping a thin layer (never too thick). If you form too thick a layer of coffee grounds, it could compact and prevent water and nutrients from reaching the roots of the plants.
Finally, if you want to make a handy liquid coffee fertiliser, take the coffee grounds and dilute them in water overnight. Then use it the next day like any other liquid fertiliser: water it directly onto the plant. This solution, although more difficult, is less acidic (and therefore less aggressive) than using liquid coffee directly.
Liquid coffee for plants
Is liquid coffee good for all plants? No, it is not. Some tolerate it, but in others, it can be harmful. We suggest that if you use liquid coffee on plants, you should first find out if your species tolerates it, and of course, if in doubt, do not use it. We can only use liquid coffee on acidophilic plants, which need acidic soils to grow.
How to use: A small cup of coffee a week is more than enough. If you overdo it, the damage can be irreparable.
The big problem with liquid coffee on plants is that the infusion process greatly increases their acidity. There is no fixed rule, as different coffee infusions result in varying degrees of acidity. Still, in general, it is always advisable to dilute it with water (the more, the better) if you want to use liquid coffee as a fertiliser for your plants.
Making compost with coffee
Finally, another way to use coffee grounds to fertilise plants is to use them as a natural compost mix. If you make your substrates, you can enrich them by pouring them into the leftover coffee grounds. You will enhance its qualities and improve the compost in the same way you supplement the soil if you pour it directly into the soil.
However, if you use coffee to make compost, there is one simple rule to follow: coffee should never make up more than 20% of the total compost.
