It’s not wrong per say, but I would discourage doing it this way. By doing it this way your “base” script will need to handle all the work and will need to be updated every time you want to add or update behavior.
I honestly think what @hinaryluna mentioned in this post is a better approach:
This clearly encapsulates the behavior for each plant type separately. I don’t understand what’s wrong with this approach and why not just go with it?
I don’t see why that would be a problem to have 20 scenes. But if you don’t want to have 20 separate scenes, you can construct your whole object with preload() functions, which would work even without a specific .tscn file. Here’s a short explanation how this could be achieved with StateMachine, but the same approach can be used to construct any node type.