My buddies at work eat a lot of bananas. And when I remember, I jack the peels. Free fertilizer for my plants, because the peels are rich in potassium. (One of the ingredients in the store bought fertilizers.)
Fertilizer has that N-K-P labeling on the bag. The potassium (banana peels!) is the K part of that triple letter fun time. (N is for Nitrogen and P is for Phosphorous.)
I chop the peels up (think like a diced onion) and then dig holes around my plants and bury the pieces. Roses especially love them. I’ve heard of people burying them whole, blending them in a blender, basically do whatever you feel like. The important thing is just to get them in the dirt.