Egg shells as pH buffer in compost?

15 years ago

Hi guys, I'm new to this forum and this place looks awesome!! I'm obsessed with gardening - it's my new hobby as of about 6 monts ago...

Anyway, I wanted to ask about using ground up egg shells in my compost. I've been saving up my egg shells after cooking breakfast and baking them in the oven when I am cooking food anyway (to avoid wasting energy). I then grind them up with a pestle and mortar to a fine talc-like consistency.

I normally use the egg shell powder in my wormery to help them eat their food since they have no teeth. However, I was wondering whether it's at all possible for me to use it as a substitute for dolomite lime? If so, will it work as well as dolomite? I'm hoping it will work well, so that I don't have to pay loads of money to order dolomite lime online and I can do my bit to save the environment!!

Featured Answer

gardengal48 (PNW Z8/9)

4 years ago

Eggshells may break down but they never fully decompose. And this has been substantiated by scientific trials. By 'breaking down', I mean that any physical activity that involves the egg shells breaks them into smaller and smaller pieces so no obvious visible evidence that the shells remain. That includes adding to the compost (where even the weight of other ingredients can shatter them, let alone turning, etc.) or activities of soil organisms and plant roots exerting pressures. A reasonable assumption to conclude that because they can no longer be seen or recognized as egg shells they have decomposed but those individual shell pieces - regardless of size - will remain intact indefinitely.

There are actually archeological digs that have found evidence of egg shells that are more than a 100 years old. And still almost fully intact.

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Comments (7)

Kimmsr
15 years ago
Egg shells will provide Calcium to your soil, eventually, but I have seen nothing to indicate they have enough Magnesium to be a substitute for Dolomitic Lime.
leira
15 years ago
I put egg shells in my compost without baking or crushing, though sometimes I crush them (on purpose) when I'm turning the compost.

As kimmsr, said, they'll add calcium to the soil eventually. I find that I still have visible bits of egg shells in the compost at the time I would otherwise call it "done," but I put the compost into the garden anyway. Since the older egg shells seem to be more brittle and fragile than the newer ones, I assume that minerals are starting to leech from them even by the time they get to my garden. Also, since my garden doesn't seem to be turning into a pile of egg shells, I figure it's all working out.
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gardengal48 (PNW Z8/9)
15 years ago
Egg shells are about 60% calcium carbonate (CaCO3) so are an effective neutralizer to an acidic soil. They do not contain magnesium in any significant quantity so not a true replacement for dolomitic lime (CaCO3 +MgCO3). However, because of the lower concentration, you will need a LOT of egg shells to make the same change as using lime :-)

And you will also need to be aware of the buffering capacity of your soil as periodic reapplication will most likely be required to maintain a specific pH level.
flora_uk
15 years ago
Hi organic - I was just wondering whether there was a reason you thought your soil needed liming? Few UK garden soils are acidic and if it's just for liming the veg plot for brassicas you'll need a heck of a lot of egg shells. I'd just stick them on the compost heap and save your energy with the grinding.
Ty Buchanan
4 years ago
last modified: 4 years ago
Tests have shown that eggshells added to soil never, I mean never, break down. It just stays there doing nothing. It takes decades to even become a powder. An idea floating around from some scientists is the boost in tomatoes is caused by eggshells improving water drainage.
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beesneeds
4 years ago
Eggshells absolutely break down. It just can take a long time depending on how they are composted. But not decades. Otherwise there would be heaps of them lying around doing nothing in the wild.

What a strange necropost.