If you have acid soil it may be ok, if you have alkaline soil there is a limit to the amount of egg shells. How many per week are we talking about?

I've read that coffee grounds aren't acidic. Coffee is, but once brewed the coffee has acid, but the grounds do not. I think the calcium from eggshells isn't a lot and it is slow releasing even when ground as you do it.

Rains wash the calcium out of the soil, so I am not concerned with too much calcium added here even when about 2 dozen eggs a week.

How many per week?
What I do is save up the shells, and grind them into a jar. I weighed a jar-full, and it was 870gms. When I shred a few sacks of garden waste, I add the coffee grounds (which have been saved up over a couple of months or so) with their filter papers, and throw in a few handfuls of the ground eggshells. My soil is Neutral anyway.

Coffee grounds & other coffee waste are a low acidic of
6 to 6.9.
I have two soil tests to prove it.
What is your source?

Maybe 100 eggs a week is too much, if you have alkaline soil. If you have too much calcium that can be harmful. If it just what one family eats not a problem.

Yes, you can have too many eggshells, essentially calcium carbonate (CaCO3), in soil/compost. It's not so much that you should be worried about an actual Ca toxicity; rather, it's eventual impact on pH and the increase in the likelihood that it will cause antagonistic deficiencies of (primarily) P and K.

Many growers think that because a particular substance is known to be high in a particular nutrient that it is necessarily a good thing. Egg shells/Ca is a good example. Eggshells have the potential to benefit ONLY if the soil is deficient in Ca. If the soil is NOT deficient in Ca and you add eggshells anyway, there is NO potential for benefit - only limitation.

Technically, there is only 1 optimal level of fertility and 1 optimal ratio of nutrients to each other. Both need to be in play at the same time for plants to realize their potential. Additionally, in many cases cultural conditions impact nutrition, which adds yet another layer of intrigue to the business of determining how to best provide for our vegetative charges.

Al

I know what you mean Al, too many people add too much stuff thinking more is better. I think I will stop adding egg shells. I can put them in city compost. I have been doing it for like 20 years, but we only eat few eggs. But, if you had a brunch place and could come with like 100 eggs I week, I know that would be too much.

Thank you for all comments received. My reason for adding eggshells to the compost bin in the first place was merely as additional ingrediant. In future I shall channel them through the Council Food Waste bin.

Re: Coffee source; these are from packs of home-brewed vacuum-packed ground coffee.

I add massive amount of starbucks coffee about 25 pounds a week, you can't get enough coffee really, just have to compost it.