What are the soil requirements for growing orchids?

Orchids originate from open woodlands and valleys, growing in slightly acidic soil rich in humus. When growing orchids at home, you must follow this growing environment and use a potting medium that is loose and airy, drains well while retaining water and nutrients, with a pH of 5.5-6.5. There are many materials that can be used as potting medium, such as leaf mold from the forest, coarse sand from rivers, household coal cinders, and easily collected sawdust, charcoal bits, plastic foam, decayed tree bark, broken brick pieces, rice husks, sphagnum moss, spent mushroom substrate, commercially sold Xiantu soil, perlite, and more. But each material has both advantages and drawbacks. For example, leaf mold collected from the mountains contains plenty of humus, is loose and airy, retains water and nutrients, and is slightly acidic, which is very beneficial to orchid growth. But its particles are fine, it drains poorly, and it easily compacts and lacks oxygen, causing root rot. Coarse sand and coal cinders have good granular structure and strong air and water permeability, but they retain water and nutrients poorly and dry out and lose moisture easily.