EGGSHELLS 101
When my granddaughter was two years old she randomly asked me out of the blue where flies come from.
It’s a good question given that, in winter, they are nowhere to be seen but once the weather warms up they are suddenly everywhere.
Clearly, she had been pondering this deep philosophical question.
Along with, perhaps, the meaning of life.
(which is of course 42).
I thought about my granddaughter when I recently re-visited a client’s property.
We had incorporated a raised vegetable garden into the design and when I had a bit of a dig around it was pleasing to see the soil blend we had specified was literally jumping with earthworms.
And in the same way my granddaughter did with the flies, the first question I had was where did all those come from?
Then my attention was drawn to the many broken bits of eggshell that had been incorporated into the soil.
How much of a part did the eggshells play in creating such favourable soil conditions for earthworms?
Unfortunately, probably not a lot.
It’s not that there is no nutrient value in eggshells.
Quite the opposite.
They are chock full of nutrient, particularly calcium.
Typically, chicken eggshells contain around 40% calcium plus a bunch of other nutrients such as magnesium, sulphur, sodium, potassium as well as organic matter (found in the inner skin of the shell).
And just like lime or dolomite the calcium is in a carbonate form which, in practical terms, means it is slow release (although the definition of slow does vary somewhat based on a factor I describe shortly).
So, potentially, eggshells could be used to help maintain the calcium levels and therefore pH of your chosen soil.
But if you’re going to incorporate eggshells into your garden or vegie bed soils, two things:
Firstly, if your soil pH is around 7 (neutral) or even above that (alkaline), there will be no response from doing this.
Soil acidity is required to dissolve the calcium and make it plant available.
Which brings me to my second point.
Particle size.
If you simply break some shells into small pieces and incorporate them into the soil, do not expect that they will do anything.
Its’ all about surface area for the soil acidity to work on.
And with larger particle sized crushed eggshell there simply won’t be enough.
It needs to be ground finely to a powder to maximise the surface area exposed to the soil acidity.
As for adding eggshells to compost.
No problem.
How much direct benefit it will be to the compost, though, is a bit like asking how long a piece of string is.
Because compost pH varies during the composting process (including going through an acidic stage) and the finished compost pH is a factor of both the length of time of the composting process and the components of the compost.
Typically, the finished compost might be between pH 7 and 8.
But just as with soil applications, ensure the eggshells are finely ground.