The advice to add egg shells to the garden or compost pile is very common. In my last post I looked at some evidence that suggested eggshells do not break down in a compost pile or in soil – at least not very quickly. The one exception where eggshells do break down is very finely ground eggshells added to acidic soil .
How quickly do eggshells break down in soil? Is it 6 months or 5 years? Maybe it’s 100 years? No one seems to know. In this post I will describe a 6 year study that has been started to find out if eggshells decompose in that period of time.
The goal is to see if there is any visual decomposition of eggshells in the soil over a 6 year period. Do they get soft and brittle over time? Do they slowly disappear?
I picked up 5 nice containers from the dollar store that had lots of holes in the side walls. I added more holes in the bottom. The purpose of the plastic container is to protect the eggshell while I bury it and then later unearth it. I want to a make sure any degradation is from natural causes, not my clumsiness.
The holes will allow water, chemicals, and microbes to move in and around the eggshell as if the container was not there. Larger rodents should be kept out.
A crepe breakfast provided lots of eggs. I tried to keep half eggs intact as much as possible. They were not washed, and each one had a bit of hardened egg white in the bottom. This extra organic material should improve any microbe activity taking place on the eggshell. The inner skin was also kept intact.
Each of six containers got one half eggshell with soil at the bottom of the container, and inside the eggshell. The eggshell is fully covered by soil. The containers were then dug into the soil near a blue spruce, in an area that should be safe from my wonder shovel. My soil pH is 7.3.
The plan is to unearth one container in each of the next 5 years.
Hypothesis – Eggshells Do Not Decompose in the Garden
Lots of people, in fact most people, say that the eggshells degrade in composts bins and in soil. My hypothesis is that they don’t degrade, except very slowly. Instead, what happens is that the act of handling the compost, spreading it, digging it into soil etc, breaks the eggshell into small pieces. Once the pieces are small enough – people do not see them, and they think, that they have decomposed.
I expect that even after 5 years, the eggshells will be complete and showing very little degradation.
Eggshell Decomposition Study – Year One
After a year under ground, one shell was dug up and examined. Details can be found in Eggshells – Decomposition After One Year.
The inner skin was completely decomposed but the outer shell was intact showing no evidence of decomposition.
Eggshell Decomposition Study – Year Three
After three years under ground, one shell was dug up and examined. Details can be found in Eggshells – Decomposition After Three Year.
The outer shell was intact showing no evidence of decomposition.
Eggshell Decomposition Study – Year Four
Watch all the details in my video.
Eggshell Decomposition Study – Year Five
The 5 years is now up and I removed the last container of eggshells. They don’t look any different than after 1 year.
Eggshells in my soil will last many years before they decompose. They are adding no nutrient benefit to the soil.
Eggshells Found in Archeological Digs
After I started this study I found several references to archeological digs that examined the food people were eating at the time, by looking at eggshell fragments. some of these were over 100 years old. Eggshells last a long time in the soil.