Hello :D I'm quite new here, and i'd like to know what's the purpose of the Gardens (other than planting an Aeanoid Seed there)? Can we pick other kinds of seeds that aren't boosters either and plant in there? And also, what's the rewards?

You can grow all sorts of seeds there. Here's a list on SubetaLodge of items which grow from seeds. You can check all of them here to see what uses they have. :)

ah thanks :D Was in doubt.