Eggshells – How Not to Use Them in the Garden

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Robert Pavlis

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 in the garden
Eggshells in the garden

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.

YouTube video

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.

Soil Science for Gardeners book by Robert Pavlis

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.

Start Seed in Eggshells
Start Seed 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:

  1. Characterization of Avian eggshell waste: http://www.scielo.br/scielo.php?pid=S0366-69132006000400004&script=sci_arttext
  2. Main photo source: Phu Thinh Co
  3. Seedling photo Source: Anthony Rossos

 

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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!

103 thoughts on “Eggshells – How Not to Use Them in the Garden”

  1. I’ve had some experience with egg shells since I had chickens for a few years. I’ve always saved the eggshells, dry them once I have a good amount, then crush them. After add them to a compost heap or a worm bin. Both compost still have eggshell residue after composting for months. I agree, from what I have observed, that eggshells do not decompose easily. I find egg shell bits in my soil every now and then, and these are probably from years ago. Anyway, I thought of another use that I will try today which is crushing the eggshells into bigger chunks and use them as mulch around trees. I think it should work since the egg shells are dry and they are tan/white so it will reflect the heat effectively. I might post it on the Facebook page once is done. I don’t foresee any potential problems but let me know if you do. Thanks for the article.

    Reply
  2. I am homesteading now and have chickens and ducks. I save my eggshells, dry them with heat and give them to my chickens to eat when they want them. I also turn some into powder to use as a soil amendment in my soil. I don’t give the chickens powdered shells or large pieces in the soil. This has been a great way to use t to hem in multiple ways. I also save chicken bones to cook until soft, then crush them, then powder them and keep for bone meal.

    Reply
  3. In summary/quick list/answers, is there any real purpose for eggshells in gardening? Is it safe to put In compost piles? What do people with backyard or homestead chickens do with all those shells? Thanks.

    Reply
  4. Trevor John Harwood: this is VITAL info to me. No one has info about curry trees and I have a little one. When I bought it, it was thriving… in clay living in a store. It is “not supposed to do that” I repotted it in “the proper soil” and 3 or 4 layers of bottom branches just fell off! It looks much happier I dosed its soil with neem powder (traditional fertilizer) and I have lots of little shoots growing out of its top and no more fallout. But the eggshells are up next when she comes inside since I live in Indiana and she won’t be able to handle winter.

    Reply
  5. I found out the hard way that eggs do not decompose. I used to raise ducks, and found a huge abandoned nest that was well hidden…and full of ticking time bombs. I buried them in the bottom of my compost pile and promptly forgot about them.

    Imagine my surprise when I dug up the area nearly 6 years later, and they were still intact. Oh, and highly explosive. I don’t like to talk about that, though. Pretty sure the neighbors still hate me.

    Reply
  6. Some years back I planted a Curry Leaf Tree, for years it did nothing, stayed at knee height. Two years ago I gave it a treatment with fine ground eggshell, I am now able to sit under it. I really believe the eggshell did something.

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    • Yes – that is what most trees do. They sulk for a few years until they get settled and then they grow – the eggs had nothing to do with it.

      Reply
    • Hi Robert. Growing cape Gooseberrys here in north Queensland Aust. (hot and dry) has been difficult. They start off really well, flower and fruit then rot just above the roots. Have followed the growing tips, have you any ideas?
      Then how about this, just recently a rogue cape gooseberry appeared in the garden, it looks quite like the cape gooseberry but it has an all-white flower. Could this be the rare cape gooseberry found in a tropical jungle? Most importantly is it edible?

      Reply
  7. Your experiment in zone 5 and whatever humidity level may give different results from a zone 7 with lots of moisture in rainfall and humidity. I’m thinking of a composting dog poop bin we had in Idaho. ( low rainfall and low humidity). After a year we dug the whole thing out and threw away a solid block of dog poop. Not enough moisture.
    Will your experiment include different levels of “crushed” and different levels of moisture? Or different sites? Different soils?

    Reply
    • Because the “articles” you refer to are mostly written by people who copy other people. Many of these are written by writers with no gardening experience.

      They also do not include links to the scientific studies that support their conclusion.

      Reply
  8. Hi there, I was wondering if there is any benefit of watering plants with the water used to boil eggs? Is there any added nutrition at all, or not enough to make a difference?

    Reply
  9. I’m glad I found this article. I’ve been saving my eggshells and just got a bigger bin for winter saving. Funny enough, I found this site while looking for info – has anyone else found their saved eggshells develop a chemical smell? Like a hydrocarbon, or turpentine. It’s not my container as I’m storing in a stainless bowl. Weird enough for me to vacate them out of my porch and into the compost bin.

    Reply

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