Sand is an incoherent sedimentary rock that derives from the disintegration of pre-existing rocks. For plant cultivation we basically consider three types of sand:
quarry sand: derived from atmospheric decomposition especially of silica rocks. In fact, the sand is composed of 95% silicon oxide (SiO2) and the rest of quartz (not used by plants);
river sand: it is the sand that we find on the banks of rivers. This sand, in order to be used, must be sterilized well as it contains numerous nematodes (worms from a few millimeters to a few decimetres, parasites or free-living, which are found in fresh water, marine or damp soil) that would damage the plant;
sea sand: it is the sand that we find by the sea. This sand cannot be used as it is for the cultivation of plants as it contains very high concentrations of mineral salts (sodium chloride) which are harmful to the plants unless repeated washing is carried out to desalinate it (operation not easy to carry out in a domestic environment. ).
In plant cultivation the best sand is therefore quarry sand, especially the crystalline one, very light yellow in color formed by very small particles as the coarse one would not blend well with the other components of the substrate. Its function is to be added to the various cultivation substrates to improve their permeability to air and water as it has a poor holding power of water and nutrients. It is important not to exceed with its use because it would cause the washing out of the nutrients and of the water itself.
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Video: Classification of Sand. Types of Sand. Construction Sands