This is similar to the carpet issue I think. When I hover plantables/walls over sparkling pools and the "craters" found in Battleground biomes, the placer is green, which implies the plantable/wall could be planted there, but the sparkling pool/crater seems to prevent the corresponding mouse prompt from appearing and so the plantable/wall cannot be placed. This doesn't seem to be as much of an issue with craftable structures, however.
So either we're not supposed to place stuff there, in which case, the placer should turn red, or we are supposed to place stuff there, in which case, we should actually be able to.
Steps to Reproduce
1. Hover plantable or wall over crater/pool. 2. The placer is green, indicating it can be placed, but no mouse prompt appears.
This issue has been fixed in either a future version or updated in a previous version.