What are the common methods for disinfecting growing media? A detailed explanation in this article

Before mixing, the growing medium must be processed to grind off sharp edges so as not to damage the roots. It is then disinfected. The common disinfection methods include: steam disinfection, chemical disinfection, sun exposure and freezing. 1. Steam disinfection Any device can be used; simply passing steam through the growing medium for 1 hour can kill weed seeds, insect eggs, fungal spores, bacteria, viruses, etc. Before disinfection, the growing medium should be sun-dried or air-dried so that the steam can be more effective and the result better. 2. Chemical disinfection Fumigation or spraying are both acceptable. For fumigation, methyl bromide (CH3Br) can be used; disinfecting for 24 hours in a sealed fumigation machine can completely remove all kinds of pathogens and pests, and it is the most thorough method of disinfection. However, because fumigation machines are rather expensive and ordinary orchid nurseries do not have such equipment, spraying with formalin (40% formaldehyde) diluted with 50 times water is commonly used, at 400 mL per cubic decimeter; after spraying, seal for 2 weeks, and after opening, leave for 10-20 days before use. 3. Sun exposure Spread the growing medium on a concrete surface and let the scorching sunlight shine directly on it for 3-7 days; this generally can kill fungal spores and insect eggs. 4. Freezing In a low-temperature freezer, freeze at minus 20°C for 24-48 hours; this generally can kill weed seeds, fungal spores and insect eggs. Because large-scale disinfection is expensive, before disinfection you can pick out the tiles, broken bricks, rubble, pottery stone, charcoal, etc. from the growing medium and simply wash them with water, while effectively disinfecting the organic matter, especially the powdery and granular growing medium that readily harbors pathogen spores, insect eggs and weed seeds. However, sphagnum moss is a living plant and can only be washed, not disinfected. (Chen Xinqi, Ji Zhanhe)