Gardening Myths About Eggshells Abound. There’s the Myth About Having to Crush Eggshells Before Adding Them to Compost Bins, The One About Having to Wash Them And The One About Them Deterring Slugs. There’s Also The Blossom end Rot And Eggshells Gardening Myth. Here’s The Truth About Eggshells

Chicken Eggshells
Chicken Eggshells

I see so many posts about how chicken eggshells can be used in the garden. And they can be used. But much of what I see is wrapped in muck, mystery, myth and untruth.

The problem often is that people believe all they are told. So gardener one reads a load of tosh and tells gardener two who tells the bloke down the pub. OK, passing on good advice is to be admired. But is everything everything you  read good advice? Where’s the evidence that it’s true.

Let’s start with the simplest to refute and move on from there.

Eggshells Stop Slugs and Snails

No, they don’t. If you’ve put down eggshells and had no damage it doesn’t prove that it’s worked. It just as likely that you wouldn’t have had a problem without the eggshells. What happened last year doesn’t make any difference to this year.

But let me show you some evidence.

It seems to me that the slugs were determined to cross the eggshells and leave via the area that had no eggshells!

All the theories about slugs being cut or dried out by the sharp edged eggshells don’t seem to be very reliable.

Eggshells Break Down Fast in Compost Bins and Add Calcium to Your Compost

Eggshells are mainly composed of calcium carbonate. In fact it’s about 95% of the dry eggshell. The rest of it is around 0.3% phosphorus, 0 .3% magnesium plus minute traces of sodium, potassium, zinc, manganese, iron and copper. Plus there is quite a bit of protein in the inner shell membrane. More on that later.

But sadly they do not break down that fast in compost or neutral soil. Put some on or into neutral soil and they can still be seen years later. Acid soil is different, the acid acts on the calcium and breaks it down. But again it’s not that fast. They can last years unless it is extremely acid.

The evidence that eggshells take ages to break down in soil isn’t just that I see them in my soil. Archaeologists often find them on digs. And they have carried out research into how long eggshells take to break down.

Of course if you break the shells into powder it will soon disappear in the soil. But that doesn’t mean it breaks down in the soil, just that it is a fine power and hard to see.

Eggshells Provide Calcium To The Soil

Only in the long term. The reason is simple, they take ages to decompose. And anyway, most soils aren’t deficient in calcium. Most have plenty of calcium for your plant’s needs. Unless your soil has a proven calcium deficiency it’s unlikely that eggshells will make any difference.

Eggshells Prevent Blossom End Rot in Tomatoes, Aubergines and Peppers

If that were true I can assure you that commercial tomato, pepper and aubergine growers would be the first to know. However, having been a commercial tomato and pepper grower for over a decade I know they don’t use eggshells.

As most soils and compost aren’t short of calcium adding eggshells to the soil makes no difference. Calcium shortage is involved in BER, but it is not due to a shortage, it’s due to the inability to transport it around the plant.

More Gardening Myths About Eggshells

Eggshells Feed the Soil

Here’s one I can agree with. Though technically it’s not the shell as such but the membrane that lines the shell. If you don’t wash out the eggshells that membrane and the bit of egg white / albumen it contains will go into your compost or soil. And as it breaks down it will provide nitrogen to the soil and plants. It’s a relatively small amount, but worth having.

Eggshells Should Be Washed, Oven Dried And Crushed Before Being Added To The Compost Heap

I hear some very strange reasons for the above claim. In my view it’s all a myth. Crushing isn’t going to make much difference in the compost heap except its harder to see the bits. It certainly isn’t going to decompose quicker as can be seen above.

I’m told that if the eggshells aren’t washed out they will attract rats to the compost heap. I doubt this very much. An eggshell weighs about 5 gram and the egg white and membrane will be around 5% of that weight at most. So around 0.25 gram if wet. But of course it will dry out and weigh less than that in many cases.

So do we really think a rat will be attracted to such a minute amount of egg white? I spent years working on farms and market gardens. I’ve seen plenty of rats and I know they are great survivors. They will find much better pickings than less than a quarter gram of egg white per eggshell. A single grain of barley will be better pickings than the eggshell debris.

As for oven drying the eggshells. Why? No one has given me a satisfactory explanation yet. Ive heard some strange reasons though. One person told me they would rot down quicker when dry. They couldn’t explain how you kept them dry when you put them into a moist compost heap. They couldn’t explain how anything that was dry could rot down. Decomposition requires moisture!

Eggshells Make a Great Plant Mulch And Suppresses Weeds

Really? If they weigh around 5 grams per egg how many do I need to cover the weeds deep enough to suppress weeds. Several kilos I should imagine. I love eggs but it would take me years to save a kilo of eggshells.

Eggshells Make a Great Organic Pesticide

Not really. Well not unless you calcine the calcium content of eggshells at 600C and then apply it in a liquid at a rate of 517mg/l. And the only evidence even then is against one specific insect pest of cotton in the tropics.

Like many of the egg myths there is a scintilla of truth somewhere in the general myth and a great deal of imagination thereafter. Yes, eggshells have been tested as an alternative source of calcium for an insecticide  against cotton leafworm infestations. But as can be seen from the research paper it has to be heated to 600C during manufacture. So spreading a few crushed eggshells around our gardens isn’t going to have quite the same effect.

There are a lot more Gardening Myths via the following link

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9 thoughts on “Gardening Myths About Eggshells

  1. Jim hand says:

    Leave eggshells to dry, then Wizz them to a fine powder in a coffee or spice grinder. Works for me

    1. Stefan Drew says:

      I’m glad it works for you Jim. But are you sure its the eggshells that are helping and not just coincidence? The slugs in the video and ones I see just crawl all over eggshells, however finely they are crushed or wizzed.

  2. Peter Robinson says:

    That’s a shame, I have always added crushed egg shell to my pots when planting the final place for my tomato, I always add dried banana skins….don’t tell me that is a myth?

  3. Philippa says:

    I had always thought they were added to provide some aeration in the compost in much the same way as grit.

    1. Stefan Drew says:

      They undoubtedly add a very small amount of aeration but organic material decomposes very well without eggshells.
      In nature no one adds eggshells to heaps of organic matter before it decomposes. But it rots just as easily.

  4. nicola says:

    is there anything egg shells are good for in the garden?

    1. Stefan Drew says:

      I’d just add lightly crush them and add to a compost bin. Over time they’ll slowly break down and will do more good than harm.

  5. Dave Jones says:

    Despite all the above I shall continue to chuck my eggshells into the comport bin where they are more likely to do good than harm1

    1. Stefan Drew says:

      I don’t disagree with that. In fact I do the same. They’ll do good, just not as much as the myths claim

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