For a direct inference for the proto-Germanic word for "plant-people" one might arrive at something like :
Buskfulk(a) (Bush-People) or even Walthfulk(a) (Forest-People)
The latter formation is well attested in the development in North-Germanic and English languages:
- bjergfolk [Danish, Mountain-people meaning trolls]
- troldfolk [Troll-people in Norwegian]
- herefolc [Old English poetic term meaning an army, band or congregation, usually military related]
- Englisce folc [Middle English term used to refer to the English]
- Lundenisce folc [Middle English term used to reference Londoners]
The term used to refer to a group of people even appears in West-German although less frequently than in the North-Germanic languages. For example, the infamous Modern German "Herrenvolk".
The only caveat here is that this term may appear to indicate that these people lived in the forest or thickets, rather than being made from plants.
Buskmann(iz) (Plant-persons) or Walthmann(iz) (Forest-persons)
This formation is also well attested and may better serve the function of denoting some fundamental attribute rather than just a location of dwelling:
- wifmenn [Old English term meaning women]
- Bergmann [Norse, A miner but can also refer to a mountain giant]
- Many German words which denote a person with a given inherent attribute [Gefolgsmann, Hampelmann, Lebemann, Blödmann]
For something connecting to flooding you might end up with
Although connecting floods to plant-people might be a difficult task for one word.