Eggshells – Decomposition After Three Years

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Robert Pavlis

Three years ago I started a study to see if eggshells decompose in my soil. Details of the study can be found here: Eggshells – Decomposition Study. It is now year three of a six year study and time to have a look at the buried eggshell.

Eggshells - Decomposition After Three Years, by Robert Pavlis
Eggshells – Decomposition After Three Years, by Robert Pavlis

Eggshell Decomposition After Year Three

I dug up one of the baskets holding the eggshell and removed some of the soil. The whole thing was soaked overnight to soften the clay soil. I then gently removed the soil and extracted the eggshell, which is shown in the above picture.

It does have a few cracks, but I may have made those putting the eggshell into the basket three years ago, or I could have made them today. The inner protein skin was decomposed even after 1 year and without this the shell becomes quite fragile.

You can see that the shell is essentially intact. The surface is still smooth. If it were decomposing I would expect to see pot marks on it, and even small holes where the soil has eroded the shell. Nothing like that is visible.

Soil Science for Gardeners book by Robert Pavlis

After three years in my soil, which has a pH of 7.3 and 40% clay, there is no visible sign of decomposition.

One can only conclude that adding them to my garden is adding nothing significant in the way of nutrients.

Eggshells After Four Years

I decided to report year 4 as a video.

YouTube video

If the above does not play, try this link:

What About Year Two?

Eggshells - Decomposition After Two Years, by Robert Pavlis
Eggshells – Decomposition After Two Years, by Robert Pavlis

For those who follow this blog closely, you might realize I missed year two. I actually forgot to post the pictures. I did dig up one of the baskets last year and extracted the eggshell, but rushed the job too much. As I was trying to get the soil out, I broke the shell. The picture to the right shows the results.

This basket had quite a few roots in it, and I suspect they might have added extra cracks making my job harder.

In year three I was extra careful not to repeat the mistake.

Even though it broke into pieces, you can clearly see the the shell has not decomposed.


To learn more about eggshells, have a look at these posts:

Eggshells – Do They Decompose in the Garden

Eggshells – How Not to Use Them in the Garden

Eggshells Control Slugs – Do They Really Work?

Eggshells – Decomposition After One Year



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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

34 thoughts on “Eggshells – Decomposition After Three Years”

  1. Robert, you said “The eggshell in this experiment was readily available to microbes – they did not do much, if anything to decompose the shell”. Can you validate this claim in some way, perhaps measurements of shell thickness, or some comparative photographs taken under a powerful microscope, or is your claim simply anecdotal evidence?

    As proven through the papers mentioned in my previous post, microbes DO decompose eggshells. All five of the different bacteria strains mentioned in those papers began to decompose the shells.

    In your reply to my comment above you state “If the surface is stable, there will still be no decomposition”. This was proven incorrect by the peer reviewed papers I mentioned. In those experiments there was microbial decomposition over the entire surface of the egg shells. Again, if you have some way to validate your claims I would love to read it.

    In your reply to my comments above you comment “If they don’t show it degrades quickly, they don’t help the discussion”. This is utter nonsense. It helps the discussion greatly by casting doubt on your unverifiable assumptions. The studies prove that microbial decomposition of egg shells occurs in soil. People keep claiming that eggshells decompose in their compost and you keep claiming that is simply mechanical damage due to your assumptions. Those studies above highlight the inaccuracies in the assumptions you made.

    You claim “The problem is that the size of particle needs to be extremely small – finer than what most gardeners will have”. What size do they need to be and where is your proof? What size will most gardeners have and where is your proof of this? You also claim “This study shows that even though you don’t see them – they are not decomposing”. Where is your proof of this, or is it anecdotal evidence based on your false assumptions? You should spend some time pondering this and decide what you think instead of contradicting yourself in replies like this.

    I sure hope that this experiment is not included in your book! If I were you I would remove this page, spend an afternoon reading papers that have been published, then re-write this page and base it on proof rather than the anecdotal evidence it seems to be currently based on.

    • It will be in my new book – Garden Myths, Book 2.

      Brix measures mostly sugar content. It certainly does not indicate nutrient dense food. Not sure what it shows about plant health, but I doubt it shows you anything of value.


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