From;
Myths about banana peel
"0.6-0.4-11.5
The NPK value for banana skins is 0.6-0.4-11.5. But this is the value for dried banana skins since all of the above values are calculated on a dry weight basis.
The NPK of fresh banana peels is 1/5 of that, making an NPK of 0.1-0.1-2.3."
Look at the NPK. It is very high in potassium relative to nitrogen and phosphate. That is not an ideal ratio for plants.
To compensate for this some people add eggshells! We know eggshells don’t decompose in most soil, and how would adding calcium balance the problem?
This idea probably started because people believe bananas have a high potassium level, and we have the very common myth,
that potassium stimulates roots – which it doesn’t.
From this misinformation it naturally follows that banana peels stimulate roots and flowers on roses?
"Banana peels are just another form of plant-based organic matter. Add them to the compost pile, or spread them on the ground to decompose.
They will add value to both the soil and plants but they are not a superfood."
Don’t get hooked in by all the crazy ideas on the internet.