Adding to that, at our regular meeting last week the one professional bonsai person in the area spoke on fertilizer, including trace elements.

He said that calcium is necessary in small amounts to enable plants to take up nitrogenand phosphorus.

So, I guess I will continue to collect egg shells, dry them, grind them up, and put a little in the soil mix.

Ivan Mann wrote: Adding to that, at our regular meeting last week the one professional bonsai person in the area spoke on fertilizer, including trace elements.

He said that calcium is necessary in small amounts to enable plants to take up nitrogenand phosphorus.

So, I guess I will continue to collect egg shells, dry them, grind them up, and put a little in the soil mix.

Why?

Calcium is in water unless you use pure water. But tap water normally has calcium.
I really do not think it is a great idea. Lime buildup is a MUCH bigger problem and risk than calcium shortage. Except for a few rare species, all trees like slightly acidic soil. Adding calciumcarbonates to the soil is not a great idea.

In the beginning of growing peppers, i used to use powderd eggshells for growing my pepper plants, as pepper plants needs lots of calcium to prevent deformed leaves and pepper blossem end rot.
I came to the concolusion, that it won't work, as egg shells release calcium to slow for plants to pick it up. If you burry and egg for 4years, you can just dig the eggs up, and it is still in one piece.
After i used a product ment for plants to add calcium, my problems with the peppers where gone. Powderd egg shells did not solve it. Waste of time.

Yes, you will need acidic water to get the shells to release ca fast enough.

Tap water here used to be alkaline and heavy calcium. Last time I analyzed it I was surprised to find pH of 7.5 and very low calcium levels. Turns out the city very kindly softened the water up and regulated the pH. That isn't acid and probably won't dissolve eggshells. That check was about three years ago, and I doubt it has changed much.

I think I will check the labels on the fertilizer and toss all the egg shells.

In USA you can buy a product called Cal-Mag as supplement for plants. (also contains magnesium)