It’s spring and even in the rain, you may still be in the garden. Hands in the ground, it’s the right season. The gardening market has never been better. “60 Millions” devotes a dossier to universal soil.
Hervé Cabibbo, deputy editor of the magazine 60 Million consumers dedicates a dossier, in the monthly magazine for the month of May, to universal soils, those soils adapted to all crops. 15 products were studied. “The “physico-chemical” results are quite correct” even if the labeling on the packaging does not always correspond to the analyzes carried out in the laboratory by the monthly magazine.
franceinfo: Are these universal potting soils really suitable for all types of crops?
Herve Cabibbo: The universal soil is designed for a very wide variety of plants. Those in the garden, like those in pots on the balcony, as much as inside the house. There are some exceptions all the same, this soil is not indicated for certain plants, for example cacti, orchids or bonsai, plants which require a very poor substrate. They should also be avoided for so-called acidophilic plants, or heather plants, which appreciate a substrate that is more acidic than average. This is the case of azaleas, camellias or magnolias.
What is in this so-called universal soil?
This soil is composed blond or brown peat, wood fibers, coconut fibers, crushed bark, that is to say mainly, vegetable organic matter. This is what ensures the retention of water and mineral salts. One can also find there, in slightly lower proportions, mineral materials such as sand, perlite, vermiculite, which promote the penetration and respiration of the roots. And a little fertilizer.
What must be remembered is that universal soil is a growing medium that has the function of allowing plants to anchor their roots and come into contact with the nutrients necessary for their growth.
You have tested about fifteen different products. Do the results correspond with what is written on the packaging?
Like many everyday consumer products, the composition of soils, which is defined by a standard, must appear on the labels, in decreasing quantity, as well as the physico-chemical parameters. The pH in particular, which is a decisive parameter for the good growth of plants. Most of them appreciate a neutral ground, that is to say a pH between 6 and 6.5. Values above or below run the risk of deficiencies or excesses. However, following our measurements, 7 of the soils studied out of the 15 have a pH equal to or greater than 7, which is much more than what is specified on the labels.
In this file, you talk about the conductivity of the soil. What does it mean ?
The conductivity reflects the richness in mineral salts of the soil. Concretely, the higher this conductivity, the more the soil is rich in minerals, that is to say in nutrients. But here too, we found differences between our measurements and the label data.
We are also interested in the ability of these soils to retain water. This is important for potted plants. For the planters, what does it give?
Yes, indeed, the ability of a soil to retain water is particularly important when it comes to potted plants, in planters, because the soil dries out much more quickly there than in the ground. It is clear from the results of our tests that not all references are equal. Of the 15 products in our test bench, 9 were rated “very good” or “good” and 3 were rated “acceptable”. On the other hand, three products out of the 15 are clearly not up to standard.
We often see on the bags of potting soil the mention “usable in organic farming”. Is it reliable?
This mention essentially refers to the origin of the fertilizers and reassures, of course, the defenders of the environment. It means that the fertilizers are natural, of organic or mineral origin. It is not certain that we can systematically qualify them as ecological compost, and this, because of the peat they may contain.
Indeed, the peat resulting from the degradation of plant debris in environments saturated with water, comes from peat bogs which are all threatened biotopes. This peat is not renewable on a human scale, since it accumulates at a rate of 0.2 to 1 mm per year. It is therefore better to favor a soil without peat. This is a statement that can sometimes be found on packaging. Or bet on a potting soil carrying the European eco-label which guarantees the absence of peat.
At the end of these tests, what is the choice of 60 Million ?
Among the good students, they acclaimed the Verve universal potting soil for its effectiveness in the shoot test, even though its pH is a little high. As for the Casino brand soil, it wins the best value for money, at 1.98 euros. This is the guarantee of gardening with good soil without breaking the bank.