- Is this mould on my bonsai's soil?
If it is mould, how can I treat it?
How can I recognise mould in potted plants in general?
If you're watering with tapwater and have done so for a while, some of this white deposit might be salts from the water; however, in reference to your other query, the salt deposits would have been present whilst the plant was in your office, and it seems you've only noticed it recently. The photograph, with close inspection, does show there is some fungal growth. Don't water for a while, and make sure its somewhere warm (not close to a heat source though, just a warm room) and the mould should dry up and disappear. In connection with your other query on this plant, this has grown because you've continued to water in the same way as you did in your office, but its clear that the temperature and humidity in your home is different - cooler temperature, likely higher humidity compared to the office.