A site pushing composting said that egg shells ground up were great for compost and for plants, but did not give any reason.

Egg shells are mostly calcium, and I would think that it would lower the pH of the soil, which might be good for some trees and bad for azaleas, etc.

Comment?

I thought azaleas liked acidic soils? Calcium is required in some of our trees processes. For 1 it is part of the cells wall cross linking that makes them more rigid. Calcium is also used as a messenger molecule in plants and us.

graysock wrote: I thought azaleas liked acidic soils? Calcium is required in some of our trees processes. For 1 it is part of the cells wall cross linking that makes them more rigid. Calcium is also used as a messenger molecule in plants and us.

So don't mix it up with azaleas?

Crush the egg shells and toss them in the soil mix for others? It's pretty much too late for this year's repotting but there is always next year.

extension.usu.edu/dirtdiggersdigest/2018/soils-alkaline

Here is a link that explains the benefits of adding calcium carbonate, a major component of egg shells, into soils. This isn't about bonsai but it does mention azaleas. Lowering the pH of soil for azaleas is a good thing. You can crush up the egg shells and add it into your soil mix or you can crush and out them on top. Maybe cover the shells with moss if you don't like the appearance of the shells.

I know the article also talks about how this is impractical but they aren't talking about potted plants. I would think this would work.

He mentions silver maple as acid loving. I have never heard that. Is that true of all maples? Japanese? Red maples?

I am not sure about all other maples either. I am newish to the bonsai hobby and don't know a ton about all the different species. I can find good Information through research! I would ask that question to some of the other more experienced people on here.

My wife usually bakes the cracked egg shells in an oven for about 20 mins (200 degree Celsius) and then grounds them into powder by using mixer/blender as it’s easier to sprinkle or mix with soil to use it in our garden. I’ve never tried it on my blue pine bonsai though. Do you think it works great with pine bonsai ?

My usual practice with something new like this is to try it on a couple of trees, see if they die or get better than the ones I don't try it on.

I'm collecting egg shells now. I'll try it on some maples and see what happens.

egg shells are calcium carbonate (96,5%) and sulfur (3%) and some trace elements. I do not know why you would add this to your substrate. I try everything to keep the calcium buildup down. Buuut.. egg shells decompose VERY slowly.

Ivan Mann wrote:
Egg shells are mostly calcium, and I would think that it would lower the pH of the soil, which might be good for some trees and bad for azaleas, etc.

Comment?

Calcium is totally ph neutral and dont affect ph at all. The eggs contains calcium carbonate, also called lime. When lime is broken down in a wet and acidic environment it releases calcium and carbonate. The carbonate part helps to neutralize the acidic environment and increase ph. If you have soil ph over neutral 7, lime will not break down and no effect on soil ph at all.

So egg shells will be very beneficial if you have acidic tap water and want to grow alkaline loving species. In this case you will find that egg shells not at all decompose slow, quite the opposite.