Bananas have long been known to be a good source of potassium for people, but not many people realize that the peel, which is also high in potassium, can be beneficial for plants. According to a report titled "Towards a Healthy Plant" by the United States Department of Agriculture, flowers need potassium for the "movement of sugars, starch formation, pH stabilization, drought tolerance, cell turgor, enzyme activation, and regulation of stomata opening and closing." By planting banana peels directly in the soil, you are inviting biological activity that provides nutrients and carbohydrates to the flowers.
Remove the skin from a banana the next time you are preparing to eat one, and set it aside. You don't need to plant it right away, but to prevent attracting fruit flies, store it in a plastic bag in the refrigerator or freezer until you are ready to use it.
Pull back some of the soil from beneath your flower plants with a hand shovel, but not too close to the stem. Banana peel treatments are especially beneficial for roses. Place the skin flat on the ground with the fleshy side down on the ground and then cover it over with the soil. Pat the soil down over it to make good contact. To avoid digging up the soil around flowers with roots close to the surface, see the next step.
Grind the peels in an ordinary kitchen blender until they are liquefied, and let sit for about 15 minutes. Pour the liquid over the soil around your flowers, and throw the pulp into your compost.
Fertilize with no more than two or three skins per week. And make sure to balance the potassium you've added to the soil with nitrogen. Studies done at Michigan State University found that red roses grown in a high-potassium environment had less red and more blue tints in their petals. When the nitrogen was too low, they had light-colored roses. Keep roses in full color by adding fertilizer, such as blood meal (1 tbsp. dry per gallon of water), to balance the nitrogen.