Almost weekly I see a post in social media extolling the benefits of adding eggshells to the garden. In this post I am going to have a serious look at all of the benefits claimed for eggshells. Which advice makes sense and which is just a lot of bull?
Eggshells – What are They?
Most of the time when we are referring to eggshells we are talking about the shells from chicken eggs and that is what we are talking about here. It turns out these eggshells contain a variety of nutrients that plants can use (calcium 34%, magnesium 0.3%, phosphorus 0.04% and potassium 0.03%). They also contains 0.05% sodium and 5% organic matter.
The organic matter might be a surprise since it is not mentioned by any gardening sites. Eggshells consist of a hard outer shell, and a soft inner white skin. The inner skin contains the organic matter. The organic content can be even higher than 5% if they are not washed out. This organic matter contains nitrogen in the form of proteins, which is very useful to plants after it decomposes.
Eggshells Keep Slugs and Snails Away
Just crush the eggshells and place them on the soil around your plants. The sharp edges cut the slugs foot and so they stay away from your plants – or so I am told.
I have discussed this myth before in Eggshells Control Slugs – Do They Really Work. This post even has a cool video showing slugs crawling all over the eggshells.
The eggshells are not sharp, at least not to a slug. They don’t work.
Start Seed in Eggshells
Save eggshell halves, put some soil in them and use them to start seeds.
I am sure this works since a seed does not even need soil to get started. But what happens once the seedling has a couple of true leaves? It’s going to be too big for the eggshell and you will have to transplant it into a larger pot. Why not do that in the first place and skip the eggshell?
Some claim that you can plant the eggshell right into the garden and since the shell is organic it will decompose. It won’t decompose quickly. Unless you crack the shell before planting, or poke some holes in it, the roots are stuck inside for a couple of years. Besides, most seedlings will need to get bigger than what the shell can provide, before planting out in the garden.
You might think that the eggshell provides nutrients to the seedling. Seedlings need very few nutrients and what they do need they will get from the soil. Besides, until the eggshell decomposes it provides no nutrients.
I really can’t think of any good reason to start seeds in eggshells.
Add Eggshells to the Compost Pile
This sounds like a great idea. Why not reuse an organic waste product?
As pointed out in Eggshells – Do They Decompose in the Garden?, eggshells decompose very slowly. The only way they add any nutrients to the compost is if you grind the eggs into an extremely very fine powder before adding them.
I wanted to better understand how quickly eggshells decompose so I started an experiment to test this, called Eggshells – Decomposition Study. I’ll be taking the first test sample this summer – stay tuned.
Eggshells contain very few nutrients – mostly calcium. Most soil in North America has plenty of calcium. Unless your soil has a calcium deficiency adding more will not help grow plants. They also have a fair amount of sodium which is toxic to plants at even low levels.
Prevent Blossom End Rot
Apparently, eggshells added to soil for tomatoes and eggplants will add the necessary calcium needed to prevent blossom end rot or BER.
Blossom end rot is NOT caused by a calcium deficiency in the soil. It is a problem in the plants where they are not moving calcium to the developing fruit. You can still get BER in soil that has lots of calcium present. In most cases BER is caused by irregular watering. Eggshells won’t help that problem.
Eggshells will help BER if your soil is lacking calcium – but most is not.
For more on this see, Blossom End Rot.
Feed Eggshells to Birds
Bake the shells to sterilize them, crush them, and feed them to wild birds or chickens. As far as I can tell this is a good way to use up the eggshells. The birds seem to eat the shells which certainly contain the calcium needed for laying their own eggs.
Eggshell Mulch
I found this quote on line, “eggshells used as mulch provide a striking accent in the garden. If you gather enough, you can even apply a layer thick enough to deter weeds.”
Who can argue with the logic? This certainly will work but how many eggs do you need to eat for a 2 inch layer of mulch? More than you eat in a life time?
If you live near an egg processing plant and can get large amounts for free, this may be a very good mulch.
Eggshells as Organic Pesticide
It is claimed that crushed eggshells work just as well as diatomaceous earth in killing beetles and other insects. It is apparently a great control for Japanese beetles.
Just because crushed eggshells and diatomaceous earth both look like white powders does not mean they work the same way.
I found lots of people on Pinterest who claim it works – that does not mean much! I found no scientific references to support the idea that it works.
Sounds like a good experiment to try this summer. For once I will be happy when the Japanese beetles arrive.
References:
- Characterization of Avian eggshell waste: http://www.scielo.br/scielo.php?pid=S0366-69132006000400004&script=sci_arttext
- Main photo source: Phu Thinh Co
- Seedling photo Source: Anthony Rossos
What about cooking them, does it still have nutrients in it for your soil if you cook them then crush them n apply?
Cooking does not change the nutrients, or make them more available – just wastes energy.
Maybe I got lucky, but I eat roughly, one egg every two days. So in the last 5 months, ~ 75 egg shells have gone into the 3 compost batches I have made. I have stirred them, used them and do not see any egg shells. In the last month to 6 weeks, I have crushed them by hand before adding them to the kitchen food scraps, but prior to that, I left them in two pieces. It certainly seems that they broke down..EVEN though the compost pile as a whole is not overly decomposed..Leaves are reasonably whole, greens are pretty well decomposed.
They are not decomposed, just broken into small bits. Chemistry works the same everywhere.
Eggshells in my wormfarm only led to a wormnursery in the hollows! Perhaps they enjoyed the membranes? Eggshells did not compost at all!
Obviously if they find ancient ostrich eggshells in the Kalahari Desert and date them to a few thousand years old, eggshells do not disintegrate!
Best use for eggshells? Powder them once dry. Eat +-½teaspoon of powdered eggshell once a week (mix into honey, jam or peanutbutter to ingest). And watch your own nails strengthen as they grow!
Regards, Inge (Pretoria, South Africa)
Would have to disagree on blossom end rot.. Placed two Tums Tablets for emergency calcium aside each plant after first set of fruit, all suffered end rot.. Second set was perfect.. Since ‘experience’, I scatter a small handful of crushed oyster shell (poultry) around the base when planting or shortly thereafter.. No more blossom end rot ever.. Eggshells still go in the composter.. Don’t care if they deteriorate fast or not, have to do something with them other then landfill.. and think they help at least minutely. Have chickens..
And if you had not placed the TUMS, you probably would also not gotten BER, since it very often only affects the first set of fruit.
What if you grind them up real fine? Would that increase the rate at which they breakdown and add calcium to the soil?
If they are ground to a fine powder and your soil is very acidic – yes.
Thank you for the info! Great read!
thank you for this, I’ve been saving the shells & ready to put them in the garden just now, well really, I’ll do it this time, but from now on they’ll just go in the worm world bin.
I found last time they were left on top of the soil (for snails), the birds liked them. Nope won’t do that again.
~ all the best, Onya (New Zealand)
since I have started adding ground egg shells to my warm farms .i believe they love it because they have multiplied immensely, grown bigger and look more healthy
Eggshells, being calcium carbonate based, will dissolve in any mild acid – chemistry 101.
In our damp clay acid soil they dissolve in a few weeks, and improve the soil as the calcium ions bind to the clay particles
In a compost heap they could be a great aid to keep it from going ‘sour’ with excess acid-producing bacilli.
But OK, on alkaline, dry, soils, or in a healthy compost heap, they may last while.
Show me some proof they dissolve in mild acidic soil. The science says it has to be fairly acidic, like a pH of 5, but I am open to new science.
I added eggshells in my composting system several years ago which are still intact😄when I add the compost to my garden the tiny bits are unpleasant when working in the soil with my hands. Won’t be doing that again, lol!
Obviously, you didn’t do it right. Eggshells have been PROVEN to dissolve in soil. You just have to accompany them with some other nutrients.
This is elementary school for gardening.
I think that is nonsense, but I am happy to review the research that PROVED this.
I’ve wondered why they NEVER seem to disappear in compost and I think it might be because they are washed during packing, wouldn’t that have an effect on them?
Just to not put eggshells in my compost for three years with all of my food waste, lots of acidic ones. When i emptied it, eggshells were fully intact still. Did not break down with the rest(and avocado skins)
Proof they dissolve in mildly acidic soil?
Apparently this guy knows what he is talking about https://www.gardenmyths.com/eggshells-do-they-decompose-in-the-garden/#:~:text=The%20study%20in%20(ref%204,at%20a%20pH%20of%206.8.
“The study in (ref 4) found that eggshells stop affecting pH once the pH of the soil is around 6.8. They stop changing the pH because they stop breaking down at a pH of 6.8.” …. that is, mildly acidic soil
From the same article “Even finely ground eggshells will have a small effect on less acidic soil.” and “When the eggshells were ground very fine, they changed the soil pH and they added calcium to the soil”
You say they dont break down, they just get crushed over time. How does that factoid interact with the statements in the paragraph above?
If eggshells didnt ever deteriorate, how many generations would it take for our egghappy society to be overwhelmed by the shells and dust? Weve been keeping chickens for 8000 years. And yes, we have a problem with what to do with industrial quantities, but youre talking about household level waste management quite specifically.
How about a sensible suggestion with what TO do with eggshells from the kitchen? That would be a productive use of your platform.
Your comments and questions are a bit confusing, Kat. Are you saying the author of the article you linked knows more of what they’re talking about than the author of this one? Because… they’re by the same person. You also misquoted them. They didn’t say they don’t deteriorate, they said “The testing found that hand crushed eggshells did NOT change the soil pH, and they did NOT increase the level of calcium in the soil. This is after being in the soil for three weeks. When the eggshells were ground very fine, they changed the soil pH and they added calcium to the soil.” The key here is “hand crushed.” Society isn’t “overwhelmed by the shells and dust” because those older shells were crushed by time and forces of nature, something humans crushing by hand cannot hope to replicate in a more viable time frame.
Thanks Robert, for interesting article.
One thing you state in your article seems to be an error – you say eggshells contain 50 ppm calcium. I think they contain way more than that. Wikipedia states they are 95 – 97% calcium carbonate (ie about 380,000 ppm calcium.)
See https://en.wikipedia.org/wiki/Eggshell which includes a reference source.
I had read that even some landfills don’t like eggshells because they attract vermin.
Thanks,
David
My number was calcium and not calcium carbonate, but even so – my number is clearly wrong. I have updated the post with new numbers.
Thanks.