Well, that depends on what kind of garden you want to have. I would really recommend buying some trees and linking them to your active schedules so you can have a visual indicator of how much you've studied. You can also buy a bunch of flower pots and grow the same type of flower multiple times to see all the unique variants.
Treea and flowers you can link to your lessons! It's fun watching them grow. You could also get a shrine if your have enough coins or a koi pond if you want a plant-based garden.
You could also get a shrine if your have enough coins or a koi pond if you want a plant-based garden.
great options 
I will try what you guys said