What should be the characteristics of the soil for succulents? In the first place it must be very draining and light, in such a way as to avoid any risk of water stagnation, which - as known - is the main cause of root rot. It should be borne in mind that these species live in stony and arid habitats, which are not very comfortable, and therefore have the ability to absorb considerable amounts of water autonomously, which will then be used during periods of drought. A sandy topsoil, consisting in equal parts of universal soil (in turn composed at least for fifty percent of peat) and sand, will be ideal for succulents, possibly adding a handful of crushed pumice stone, pozzolana or chopped bricks. The substrate based on sand and peat is perfect to guarantee the lightness necessary to ensure a smooth flow of water, and at the same time allow the root system to transpire and exchange oxygen with maximum ease. Peat, on the other hand, ensures the assimilation, through the organic substances that characterize it, of the nutritive elements that the succulent plant needs. Although usually a rapid outflow of water causes a depletion of the soil, and in particular a loss of mineral salts, this does not represent a problem for this type of plants, which from this point of view do not show particular needs. When it is necessary to bury a common succulent plant, which does not require fertilizers or specific nutrients, the soil can be purchased simply in a garden center (taking into account, however, that the cost will be greater than the price of universal soil).
If you have to deal with large quantities, nothing prevents you from preparing the soil yourself, even more so if river sand is available nearby, as long as it is coarse-grained. This sand must be filtered, in the sense that the presence of fine sand and silt would make the compost compact: precisely what must be avoided, since a compact compost prevents easy oxygenation, and hinders the development of the roots. The sand, therefore, will have to be sifted and washed several times, using a normal sieve (the one used in the kitchen, for instance) and a bucket; if you have a sieve, you will be fine with different meshes, from two to five millimeters, so as to have clean sand with different grain sizes. Moreover, in the absence of such instruments it is possible to make a DIY sieve by building a simple cylindrical container closed with a net on the bottom. So, once you have chopped some bricks and prepared the sand, it is enough to buy the universal soil to make the substrate. At this point, nothing more needs to be done than mixing the various elements, when the sand is still rather wet, so as to obtain a homogeneous compost. In order to make the draining effect more effective, it will be necessary to create three or four centimeters of expanded clay: a layer that will allow the roots not to remain wet for a long time, and that must be applied to the grid placed to protect the drainage holes before the pot is filled with soil. Therefore, after the plant has been buried, it is advisable to make a mulch, even light, with thin gravel or pozzolana, in order to protect it to a greater extent from any rotting of the stem. The pozzolana is nothing more than a material of volcanic origin, therefore natural, composed of volcanic ash, porous lava and lava material. Its name derives, of course, from the city of Pozzuoli, where this material is widespread.
Topsoil succulents: La pozzolana
Characterized by a moderate mechanical resistance, pozzolana is able to provide excellent protection, defending the soil and the fat plant from enemies such as weeds and parasites, and above all limiting the vital space for insects. Furthermore, mulching makes it possible to maintain a constant temperature, limiting the humidity of the soil: in fact, it is able to contain evaporation (for the same reason, among other things, it requires a very low water requirement) . As can be seen, therefore, the preparation of the soil for succulent plants can be done simply and without particularly demanding operations. Clearly, the advice of a professional can come in handy, specifying the type of succulent plant that you want to plant or repot. The universal soil, rich in nutrients and soft, is likely to be too moist and compact for a succulent: for this reason it will have to be lightened with river sand, which will make the substrate permeable and porous, therefore more suitable for not retaining excessively the water. River sand, it is worth repeating, should be washed so as to remove fine dust, which would risk making the soil hard and compact. The volcanic lapillus, the pumice stone and the pozzolan are all equally reliable variants, able to favor the outflow of water into the soil.