Flutter // Understanding dispose

Question

The more things I do, the more often I run across things that need disposing (e. g. Timers and ScrollControllers). Two questions:

1. Is there a way to see/know what things need to be disposed? Or is it just a thing you need to learn by heart? For example: At the moment I'm not sure, if I need to dispose of providers.
2. Do I need to expose things (e. g. Timers) in stateless widgets? If so how? Or do I turn a widget stateful just so I gain access to the dispose method? That seems wasteful.

Thanks!