The white layer are fungi that appear due to lack of light and excess watering. When the soil is always wet there is an excess of moisture from irrigation, that is when fungi emerge.
- Make sure to water when the bonsai needs it and not before. The substrate must be dry. Remember the irrigation technique:
- Insert your finger 1 cm into the substrate.
- If it comes out wet, we should not water.
- If it comes out dry, we must water. Irrigation must be abundant, that is, throughout the substrate and until the water comes out clean through the drainage holes.
- Place the bonsai somewhere that receives a lot of natural light.
- You can manually remove the first layer of soil and add a new substrate if necessary.