Banana skins are high in potassium and phosphorus. They can be used in the garden as a fertiliser just like any other fruit or vegetable scrap where they will break down and release their nutrients to the plants.
Compost
Bananas are a good addition to composts. They are full of nutrients and break down rapidly and will not attract vermin. Be sure to bury them to avoid attracting fruit insects.
Slice and Dice
Cut the used banana peel into slices and dig it into the soil around the plants. Burying it will protect the peel from ants and fruit insects. If needed the banana peel can be put straight on the ground around the base of a plant but it will take longer to decompose.
Banana Powder
Dry banana peels in the sun or on oven tray. Once dried ground down into a powder-like form and store in a paper bag until needed. Use this to sprinkle around the base of the plants, mix into the soil and lightly water.
Plants That Benefit From Banana Peels
Roses and tomatoes especially benefit from a banana peel in the base of the hole before being planted. The potassium in the peel is good for growing large strong tomatoes.