my friend told me that his neighbor throws them in his tomato garden alot. he said this dude always has the biggest nicest looking tomatoes. that was his secret. he didn't say anything about composting them first though.
I dunno about jus putting egg shells in your soil will do anything. But i know if you put it in a compost pile its really good, my dad has been doing for his garden as long as i can remember..
A good mixture of eggs & coffee grounds add calcium and nitrogen to your soil. Just grind or crush the eggshells and add that to the coffee grinds and mix it with your soil. Best test your runoff for ppm and nitrogen if you are supplememnting with other fertilizers.
Many common home throw aways can be used to help your grow.
it sounds to me one of tho's little things people do that is most prob a myth i couldnt see how much this could change your plant, any one tried it against a control group?
eggshells are good in compost piles. usually people use them for worm beds. when i grow a garden of veggies i put banana peels orange peels and eggshells in the ground a month or two before planting. it will help if you break it down. i know that for a fact.