Do you know this phenomenon? The most beautiful plants are in the flower bed and suddenly the earth sags under them. The plants slide down and hang crooked in the bed. In the garden you could assume that it is voles that undermine the bed and so the earth slides down. But what does it mean when this happens in the greenhouse or conservatory? Then don't panic, because you definitely don't have any voles there.
Organic matter in the soil
If plants only grow under glass, then organic matter in the soil decomposes. As a result, the volume shrinks and the earth sags. Anyone who comes up with the idea of simply piling up new soil should refrain from doing so. This can lead to rot. Here you cannot avoid digging up the plants and replanting them. Exceptions are bananas, palm trees and Strelitzia. These plants don't mind you piling up the soil.