From a fellow grower: "Are egg shells and banana peel chopped up to a powder beneficial to add at planting?
I’m a new grower myself, but from what I understand, organic matter like that would probably be more readily available if you composted them much earlier. It can take quite a while for the nutrients in that organic material to decay to a state that they can be absorbed by roots. Look into organic or living soil for more info.
Eggshells take years to decompose
I put them in the garden knowing its a long term supplement.
Organic waste will cause fungus/mold to develop unless as was mentioned you compost it first.
If you put eggs shells in a very low oven for a couple of hours, then crush them with a blender ,the powder you get is calcium,(good for bone growth, and strong stems ) , and if you add them to white vinegar, then you have calmac ,
Also the water you boil your eggs in is also full of calcium , and good for the water butt.