Planting materials / substrate
Unlike other houseplants, we do not cultivate orchids in potting compost but in a special orchid substrate. Why is that?
Orchids, at least epiphytic ones, do not grow in the ground in their tropical habitat, but on trees or even rocks. This means that their roots specialise in drawing sufficient water and nutrients from the moist air, rainwater and organic material in the ground.
The most important property of orchid substrate is therefore its coarse structure. This makes it permeable to air, irrigation water runs off immediately and very little moisture is stored. Ultimately, the substrate contains the amount of water that is available to an orchid in the jungle in the humidity and the surface of the tree bark. If the roots were in constant contact with moist soil, they would quickly rot.
However, semi-terrestrial orchids that grow on the ground and also have aerial roots above ground also need an air-permeable substrate. A loose material is also important for Phalaenopsis because it can even photosynthesise with its roots, provided they have contact with light.
Composition
There are various organic substrate components, i.e. components of natural origin, such as pine or pine bark, which are usually the main component of the substrate, or coconut fibres, wood fibres, cork, nutshells and moss. Inorganic material such as polystyrene, rock wool, sand and expanded clay can also be used as a substrate. Sometimes the substrate is enriched with acid lime to control its pH value. Clay granules or perlite are added to store moisture, which can be an advantage in dry indoor air.
Over the years, the substrate is decomposed by microorganisms and changes its structure: it becomes finer, compacts and stores more moisture. To prevent the roots from being damaged, the plant must now be repotted. It is advisable to use a high-quality substrate that is not too finely crumbled but is stable and retains its structure until the next repotting, i.e. approx. 2 to 3 years.
Finding the right substrate
The best way to find the right substrate is to ask a specialist, as the composition of the substrate varies depending on the orchid species and its specific requirements.
Cymbidium, for example, is potted in a mixture of pine bark and humus, while Phragmipedium feels at home in sphagnum moss.
As a general rule, the substrate for young plants should be finer than that for larger, older plants. Small orchids are therefore often potted in coconut fibre, which can store a lot of moisture and therefore supports growth.
In any case, you should not skimp on the substrate, as its quality directly influences the orchid's ability to thrive.