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.

Plant Science for Gardeners 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.

Building Natural Ponds book, by Robert Pavlis

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. After reading comments, I’m amazed how science and evidence (citations) and clarity still fail to convince some people. And how some readers want the details to make the myths work. Ha! I’ll refrain from discussing this as a commentary on our current political climate. I do appreciate the shared interest in recycling something and making less trash.

    Reply
  2. I certainly agree with you that eggshells do not compose or break down very fast. In fact in my experience they just ‘disintegrate into smaller pieces in the compost box when I dig it out.
    One thing I have noticed though is that my wood bug population that lives in my compost box really and wonder about is do they enjoy the membrane that line the egg shell, at least I see a lot of their poop inside the shells, kind of like how they really like the leek trimmings that go into the box.
    Great blog!! Thanks for sharing your information

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  3. Eggshells! great for the garden? An old wives tale, and as useful as a tit on a bull. My wife got it from her mum, and the same comment applied when she applied them. Did you hear the one about singing to your plants??

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  4. Very interesting discussion. I live on the prairies with quite alkaline soils. Will egg shells increase the alkalinity, especially in containers with garden soil in them?

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  5. I usually save the shells all winter and lay them down in the large chunks of half and quarter shells, under my tomatoes bed and then a layer of soil and the plants. I usually lay the shells out and let them be exposed to the sun for a week or so prior to planting. The plants really thrive and when I hand till the spot following year there is no trace of the shells. I also use my eggshells at the bottom of potted plants, usually in half or large chunks for drainage and I assumed added benefit of nutrients. Finally I sometimes will also use water from boiled eggs on my house plants. When you say to start seed in the eggshells, how to do this or in what vessel as the seedlings grow fast usually. Do you put them into some other container such as organic pots or plastic seeding pots?

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  6. It would be a useful addition to post the safe level of sodium. I’ve read that plants do use sodium in small amounts. Also, I’ve read that sodium is washed away, especially in sandier soils (vs. heavy clay) by water/rain. So, is the sodium toxicity from eggshells a serious concern for clay soil but not sandy soil? Is it a serious concern for soils that get little water (xeric) but not for higher-water soils?

    How does the amount of sodium in the shells compare with the amount that runs off from road salt? I used to live in a condo and tried to convince the association to mandate non-sodium salt but they ignored me. I used to get a lot of salt around my planting beds but my daylilies and irises kept going — in heavy clay.

    Since salination of soil is apparently so bad I’ve always wondered how soils can cope with all of the road salt. Do you have a post about that topic somewhere?

    Reply
  7. While visiting my daughter I repotted her Potho plant. I made some ground eggshells and water for the plant. Soil had some stick plant food also. The plant died. It looked awful rotted and yellow leaves. My daughter was upset and horrified! She does not do well with plant care. Help* Thanks*

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  8. Does soaking toasted, ground eggshells in cider vinegar produce useable calcium? It seems lots of people think so. (Just Google “eggshells in cider vinegar”.)

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  9. I set my egg shells in the sun, for a day or two, then grind them into powder in a coffee grinder, and add some each day to my Worm Farm. Worms have a gizzard & they need grit to grind their food up. I also add a couple tablespoons to each tomato plant, at planting.

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  10. Liked the information, very much. I’m still looking for that perfect formula for the Southwestern desert that is getting hotter than Hades with each passing summer.

    Reply

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