teuchter
je suis teuchter
Yeah I'm kind of familiar with efflorescence on materials like brick or concrete but don't see much reference to it being a thing on soil surface.the white stuff maybe a fungus or similar. but my main suspicion would be mineral efflorescence. Some of my earthenware pots get this from mineral-rich water leaching out through the side.
My worry is it's a mould or fungus type thing that is likely to harm things I plant in it.