In nature, orchids grow as epiphytes on trees. The orchids cling to the tree bark. They can absorb the nutrients they need by organic material supplied by wind and rain. Therefore, substrates that contain bark are particularly suitable for orchids, as they most closely match their natural environment.
In conventional potting soil, the orchid roots would suffocate from a lack of air. The basis for an orchid compost is always bark. Due to the global forestry, pine bark is the easiest to obtain in a consistent quality.
Growing orchids in pure bark is not easy. Almost none of the professional horticultural companies cultivate the plants in pure bark these days. A permanent water-storing humus should always be added to the bark i.e. sphagum, peatmoss or coconut substrate can be used for this. The choice of permanent humus depends not only on availability and price, but above all on the quality of the bark and the fertilizer used.
Soft bark such as Pinus sylvestris (Orchi-Bark) easily absorbs water, it is also easily removed again, and is an ideal option for 1-2 years. Pine bark from Pinus pinaster is significantly harder and bast-free, the bark slowly absorbs moisture after 1-2 months in culture. In Pinus pinaster (Orchi-Bark Plus) the plants can be cultivated for up to 3 years without transplanting The premium bark of Pinus merkusii (Orchi-Bark Premium) is very hard, lasts up to 5 years, but it takes a long time for the bark to absorb moisture.
Bark mulch has a very high proportion of sapwood and bast. Usually it is already in the state of deterioration and is therefore not to be used for orchids at all..