Weathered Stone Is a Common Growing Medium for Orchids: Characteristics and How to Use It

Weathered stone is a granular mineral material formed when rock gradually disintegrates and breaks apart after years of sun exposure, rain, and temperature fluctuations, and in orchid cultivation it is often screened and used as a growing medium. It is mostly found in mountainous areas and riverbank zones, and its color varies among grayish white, yellowish brown, or blue-gray depending on the composition of the parent rock. The particles of weathered stone are mostly porous inside, with good air permeability and drainage, and they do not easily compact over long-term use, which benefits the breathing and growth of orchid fleshy roots. It has a stable texture, is clean and free of humus, does not easily breed pathogens or insect eggs, and contains certain mineral components. However, it lacks organic nutrients and has low fertility, so when used alone it needs to be combined with fertilization. Before use, dust and overly fine fragments should first be screened out, then it should be repeatedly rinsed with clean water, and after sun exposure or soaking treatment it can be potted. The particle size is best from mung bean to fingertip size; it can be used alone or mixed with bark, tree fern fiber, volcanic stone, leaf mold, and so on to complement one another. When potting, large particles are often used as a bottom layer, and medium and small particles fill the middle, which is more conducive to drainage and air permeability. Weathered stone has relatively weak water and nutrient retention, so when cultivating, watering should be appropriately more frequent, and fertilization should follow the principle of light fertilizer applied frequently. After many years of use, the particles will gradually turn to powder and air permeability will decline accordingly, so new material should be replaced or added promptly. When cultivating different orchids such as Cymbidium goeringii, Cymbidium faberi, Cymbidium sinense, and Cymbidium tortisepalum, the ratio of particles to organic growing media can be flexibly adjusted according to the local climate and pot conditions.