March 4, 2024


One of the most complex garden materials to understand is the substrate. To understand it, you have to start with the definition. A substrate is simply a growing medium for plants in a container. And what is a container? Any container with a limited height where plants are grown. It is almost essential that this container have an outlet for excess water from irrigation, so that there are no root rot problems. To that substrate that fills a pot, one of the many types of fertilizer is applied from time to time, which are the necessary nutrients for the correct growth of the plant.

With these three concepts explained —substrate, container and compost— it would then be necessary to make it clear that garden soil, no matter how good it is, should not be used to fill a pot or a planter. Many times it is thought that this fertile, moist and spongy soil can also work well in a container. But the reality is different, and it ends up becoming a hard and compacted stone, in which the roots grow with difficulty.

In a growing medium we need very specific parameters. We must not forget, even if it seems obvious, that the roots of a plant cannot explore beyond the prison that a pot represents, and that within that container we must provide everything that the root needs: air, water, nutrients.

An ideal substrate should have, first of all, a high aeration capacity, which is achieved with a pore space greater than 80%. Those who have taken a handful of some good substrate in their hand, and have squeezed it, will have verified how it is impossible to compact it. This is due to this quality that it must have: that of allowing a good amount of air in the substrate, even when it has just been watered. A very heard phrase is this: “What a bad land, as soon as I water it, the water comes out of the holes!”. This is precisely what is sought in a good and professional substrate, that there is no excessive water retention once that substrate has been hydrated. In this way, the root will enjoy two of the things that make it happy, such as oxygen and water.

Thus, we see how the substrates that are marketed are made up of different components, which in turn can also be called substrates: peat, coconut fiber, perlite… Each one of them has a function and contributes some quality to that mixture. On the one hand, organic materials are usually needed in a substrate (such as the aforementioned peat or coconut fiber, pine bark, wood fiber…), which provide water retention and nutrient reserves, thus explained in a simple way. . On the other hand, in the mixtures of substrates, mineral materials are added (such as silica sand, river sand, perlite, vermiculite…), which mainly provide drainage and aeration, although many of them also offer water to the roots of the plants. floors.

Others are added to these organic and mineral components, such as clay or calcium carbonate, which improve nutrient retention or make the pH more suitable for cultivation. Finally, it should be mentioned that the prepared substrates incorporate a background subscriberwhich is a contribution of nutrients so that the plant has a fertility that allows it to grow in the first two or three months of cultivation.

What substrate should we choose?  The normal thing is to resort to a generic one, which works for a wide spectrum of plants.
What substrate should we choose? The normal thing is to resort to a generic one, which works for a wide spectrum of plants.Mario Guti (Getty Images)

Given the theory, another question comes up again: given the large number of substrates that are on the market, which one should be chosen? The normal thing is to resort to a generic substrate, one that works for a wide spectrum of plants. It is what is known as universal substrate. In this we should look at the aforementioned pH, which is the measure that indicates the acidity or alkalinity of a medium. In general terms, the suitable cultivation pH for the vast majority of the plants that accompany us in houses and gardens is in the interval between 5.5 and 6.5. That is, they are kept at an acidic to slightly acidic pH. In this way, from the outset, substrates that exceed this measure should be discarded, which must be reflected on the back of the manufacturer’s bag. Acidophilic plants (camellias, hydrangeas, gardenias, azaleas, rhododendrons…) will vegetate content with even more acidic pH measurements, even below 5.5.

Environmental problems in the manufacture of these substrates are also present, and here we must talk about peat. Both for the extraction of the blonde peat and the black peat, places of high ecological value are destroyed, the peat bogs, landscapes that took thousands and thousands of years to form. That is why these substrates are being replaced by other materials with less impact, as they do in the Rosales Ferrer nurseries, specialized in the world of roses. “We are incorporating a high proportion of rice husks into our substrates,” says Arnau García, manager of this Valencian nursery, “which is also a local by-product.” Wood fibers, another by-product of the forestry industry, or the compost of vegetable remains are other substrates that are being incorporated to stop the devastation caused by the extraction of peats.

Passionate debates between one and the other aficionados of cultivation always originate around the substrates, as is the case with cooking recipes, since it is common to compose the mixtures at home. Each person has the ideal substrate for their plants and, sometimes, the solutions of other hobbyists are seen with reluctance. It must be emphasized that, in the end, those who give us the measure of our good work are the plants themselves. A vigorous and healthy growth is linked to the choice of the substrate. Next, it will be necessary to investigate more in each one of the different materials that compose them. Healthy roots, happy plants.

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