Roses love banana peels. They rot quickly, releasing minerals roses need such as calcium, sulfur, magnesium, and phosphates. Just cut them up and mix them in the soil at planting time or anytime you want to give your roses a boost. You can also make a banana peel tonic for use after the plants are established. Just soak chopped pieces in a closed jar of water for two weeks. Pour the remaining mush under the rose bush.