Banana peels have potassium and roses love the peels. They also like coffee grounds. The banana peel should be dried because it will decompose faster that way, you can also dehydrate the coffee grounds and then both can be stored in a bag or jar so you can feed your roses on a regular basis You can dehydrate them in the oven till crisp or in a dehydrator at 135 degrees till dried, don’t go higher that 135 or you will kill the nutrients. Then just break them into smaller pieces and bury them around your roses bushes about 3 or 4 inches deep. Same with coffee grounds just bury them around the bushes. Why throw them out when your roses would love them.