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Eggshells – How Not to Use Them in the Garden

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 50 ppm, sulfur 39 ppm, magnesium 12 ppm and potassium 12 ppm) (ref 1). They also contains 21 ppm 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.

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

 

Robert Pavlis
Editor of GardenMyths.com
I live in southern Ontario, Canada, zone 5 and have been gardening a long time. 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!

I hope you find Garden Myths an educational site that helps you understand your garden better.

24 Responses to 'Eggshells – How Not to Use Them in the Garden'

  1. John A Tallant says:

    We dry ours in the microwave, crush them with a pestle and add them to the soil, they can’t hurt and doing this keeps them out of the garbage can. There is some nitrogen in the egg white and mechanically they will help loosen up heavy clay soils. Feeding them to wild birds may help spread disease to the wild bird population.

  2. germain says:

    Hi Robert. My Mamie (94) has been swearing by eggshells all her life… I seem to have inherited her compulsive habit. I am now looking after a camelia and I’m slowly growing an awareness of acidic or alkaline soils​. Should I stop my urge to feed it eggshells?
    Thanks for your light-hearted​ and objective comments; never expected demystifying eggshells could be so entertaining!!!

  3. Cynthia E. Olen says:

    I just use them as an added calcium source. Keeps away slugs? That old wive’s tale is almost funny. I’ve seen slugs crawling on broken glass, so clearly a few rough edges don’t bother them. The tissue of their foot is extremely tough and the slime layer protects them further from abrasion.

    Back when I had chickens, I was always told to never feed eggshells to them because that would turn them into egg killers. Well, how does that explain the fact that my hens would apparently eat the shells after their chicks hatch, and yet never did they attack unhatched or sterile eggs? Chickens are not going to waste a perfectly good source of calcium—unlike other birds, they lay scores of waste eggs every year, and so have a higher demand for calcium than a wild bird would. If a chicken is attacking eggs, then it is for some other reason—not because you fed them eggshells. If anything, such behaviour may indicate that they are calcium deficient or in need of protein or they have become psychotic from being in a cage. So, any gardeners out there who also have chickens would probably do better to give some of the shells back to the hens rather than toss them in the garden.

  4. Iva says:

    I’ve used eggshells for a number of years for vermicomposting. We are a family of 8 and I use at least 6doz eggs a week. I dried the eggshells and then ground them into powder with my blender. I would sprinkle that powder on top of everything every time I added fresh “food” (veggie waste, coffee grounds) to the worm bin. Failing to sprinkle that powder generally meant an explosion of mites…the tiny red things barely bigger than a speck that would overflow the bin into my kitchen. Yuck. I believe the eggshell powder helped to balance the pH of the bin so that the mites did not feel like multiplying. “Food” probably increased the acidic level, while the eggshell powder helped to bring a more alkaline balance.

    I no longer have a worm bin. I’ve been soaking my eggshells along with my coffee grounds for about a week at a time in a bucket with water. Then I pour the sludge on my potted plants that don’t have access to nutrients that plants in-ground would. Then I put the grounds/shells on my compost pile. I wish I knew if the calcium from the eggshells leached into the water. Have you tried this? All I know is that the 2 potted plants I have in my house are adding leaves and blossoms and there is no way they could do this without adding nutrients to their soil. Whether the nutrients are from the coffee or the shells, or both, would be the question.

    I think that eggshells, once they are crushed, are a way of adding organic matter that helps to loosen otherwise heavy soil. Lots of things can do the same thing, but it’s why, even though I may not ‘”know” of any nutrient value they add to the ground, I go ahead and toss the shells on the compost.

    • Re: “Food” probably increased the acidic level, while the eggshell powder helped to bring a more alkaline balance. ”

      Actually as food composts it produces compost at about neutral pH or a bit alkaline. It is usually not acidic.

      Pouring water over eggshells adds almost no calcium to the water.

      since egg shells are not really organic matter – they don’t contain carbon or much in the way of organic molecules – they won’t loosen soil.

  5. meredith says:

    If you have a worm farm the worms absolutely love eggshells and break them down till nothing is recognisable. You can crush the shells, or in hot weather leave the halves whole and the worms seem to like to gather under there- it stays cooler and damper perhaps? This seems the quickest way to get the nutrients into the soil.

  6. Marie Morton says:

    I’m a fellow Zone 5 Southern Ontario gardener, and a career historical archaeologist. I can guarantee you that you can find egg shells from the 19th century in domestic historic sites. No, they don’t decompose fast….

  7. smmah says:

    Hey Robert, such a great and informative site – not to mention hilarious! Thank you, and look forward to keeping track of your writing!

  8. Margot says:

    Although I do not put eggshells in the compost because I don’t like seeing dirty white specks in the soil, I’ve been told that, unless washed out first, they attract rats. My eggshells go in the food recycling bin.

    • Roxanna Johnson says:

      Thanks, I was wondering about that. I am starting a little garden but our neighbor was telling me she saw a couple of rats in her yard so I don’t think I will put eggshells out.

  9. Steve Allgeier says:

    Good job. I have been referring the Master Gardener groups in Maryland to your site regularly. —Thanks, Steve

  10. Richard says:

    This has nothing to do with eggshells, but I would like to see you do a height of cut study for lawns. A lot of people including my neighbors think of they cut their lawn close they don’t have to cut as often. This is a myth along with all the bad results of cutting close.

    • I’ve added this to my list of future myths – a very long list.

      It is possible that cutting short reduces growth rate and therefore the number of times you need to cut the grass. After all a grass plant with no blades is not going to grow very well.

      But it also apparently leads to more weeds. so any saving in cutting time is balanced with weeding.

  11. Mike Ricci says:

    I’ll be interested to see how the decomposition study goes! Not sure about the rest of North America, but here in Maine our soils are very acidic and lacking calcium. We add gypsum annually (300 lbs/acre/year) as well as high calcium lime.

  12. Steve Morse says:

    I am continually impressed with your work… and from some of the stuff I do for California Master Gardeners (Contra Costa County… SF Bay Area)… I know it’s a lot… and I like it and share it whenever and wherever I can…
    CHEERS
    Steve Morse

  13. Joan smith says:

    I still think eggshells should go in the compost pile, not the trash.

  14. janet says:

    Thanks for the article. I will look forward to your experiment’s results.

  15. Dan OConnell says:

    Brings up memories of digging in my mothers garden more than 50 years ago…lots of eggshells all the time. I’m willing to bet those eggshells are still there.

  16. Lee Reich says:

    Just because eggshells compost slowly does not mean they should not be added to a compost pile. The same could be said for avocado seeds and peanut shells. All compost slowly but do no harm to the compost. And eventually they do decompose either in the compost pile or after the compost has been spread on the ground, adding whatever nutrients they have to the compost or the soil.

    As far as calcium in soils, plenty of soils in northeastern U.S. and in the tropics are low in calcium. Not that eggshells would be the easiest way to add calcium.