For years the belief has spread that it is enough to pour used coffee grounds onto the soil in pots to enrich it with nutrients. And it is true that coffee grounds They have their place in natural and sustainable gardeningas they have at home in many of their other applications, but you have to know how to apply them well so that they are really beneficial and do not cause more harm than good, because what seems like a simple and beneficial idea can become a serious mistake.
As the expert André Alonso (@andrealonsorc) warns, the grounds They are not an immediate fertilizer. On the other hand, keep in mind that an excess of coffee grounds can harm some specific plants.
Undesirable effects of grounds on plants
Alonso André, known on Instagram as «La Reina Plantil», explains with his characteristic sense of humor that, by placing the grounds directly on the substrate, instead of nourishing the plant, it promotes proliferation of fungi, molds, bacteria and small insects that are attracted to decomposition.
This happens because «roots are not able to absorb directly the nutrients contained in coffee».
So, coffee grounds are no good for plants? Yes, they are useful, but, like all organic material, require a prior transformation process so that they become something usable by the plant. Without this intermediate phase, we will achieve more problems than benefits.
«Coffee has to decompose, be transformed by microorganisms and become soluble so that plants can absorb it. And that does not happen when pouring it as is on top of the substrate,» clarifies Alonso.
What really happens in the substrate
iStock Photo.Nusara Angkuldee
When coffee is deposited as is on the ground, it begins to ferment and decompose on the surface. The process generates unpleasant odors and, above all, a perfect environment for the appearance of pests such as substrate mosquitoes.
Added to this is that the compact layer of coffee can harden the surface of the pot and, with it, hinder oxygenation of the roots and water absorption. In short, far from being a help for the plant, it is detracting from the quality of the environment in which it should grow.
How to turn coffee into useful fertilizer
iStock Photo.ThamKC
The good news is that coffee grounds can be transformed into a valuable resource for the care of plants, as long as they are used appropriately. The key to using coffee grounds as fertilizer is composting. The process can be done in different ways:
- Homemade compost: Mix the grounds with leftover fruit, vegetables, dry leaves and other organic waste until they decompose and become mature compost. In general, It is recommended that the grounds do not represent more than 20% of the total mixture.
- Vermicomposting: It uses California worms that digest the coffee and turn it into humus. This worm humus is a material rich in nutrients and fully usable by the roots.
Of course, there are also other uses that you can give to coffee grounds at home to reduce your waste and take advantage of the resources you already have to find solutions to the small challenges of everyday life.
Beyond coffee: other kitchen scraps
André Alonso’s advice is not limited to coffee grounds. The same rule applies to many other wastes that we tend to think of as “feeding” plants if placed directly in the soil, such as egg shells, leftover fruit, vegetables and even bread. All these materials must first go through a decomposition process.
Composting ensures that nutrients are available in a soluble form and that the material no longer generates harmful fermentations or attracts pests.
Benefits of doing it well
iStock Photo.Firn
When coffee grounds are used correctly, they do provide indisputable benefits:
- They improve the structure of the soil, making it fluffier.
- They increase the moisture retention without flooding.
- They provide nutrients such as nitrogen, potassium and phosphorus in forms that plants can assimilate.
- They promote biodiversity of the soil, by stimulating the activity of beneficial microorganisms.
The result is a substrate more balanced and fertile, which translates into better development of roots, flowers and fruits.
Isn’t coffee for all plants?
ANDThere is a notion that grounds are very acidic, but most of the acidity is lost during coffee preparation. The pH of the used grounds is usually between 6.5 and 6.9, that is, it is quite neutral.
This means that they do not over-acidify the compost, as long as they are not added in large quantities, which could be detrimental to plants that like a rather alkaline soil, such as gladioli, asters, forsythias, berries, lavender, santolina, rosemary, thyme, cabbages, asparagus or beets.