My mother in law always did this, I though it was the chemicals in the peel that made it work so well. Just flatten a banana peel and bury it under one inch of soil at the base of a rosebush. The peel’s potassium feeds the plant and helps it resist disease...works for tomato plants too.
Don't throw out the water your boil your eggs in. This water contains tons of calcium that your plants will love. Just let the water cool and dump it on your plants. I also save my egg shells, rinse them out real well, smash them up then mix them with dirt and/or potting soil before planting any plants.