It sounds like a fantastic idea, doesn’t it? Water that you’ve just boiled your eggs in can be used on the garden to give your plants a calcium boost. Just leave the boiled water to cool down, then slosh it around your plants.

But is there anything behind this?

It’s a claim that’s been circulating online for years and has now just popped up in my Facebook feed courtesy of Australian native plants company Austraflora:

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If you can’t read it, here’s the relevant part of the text:

Next time you’re boiling your eggs for breakfast, save the water, allow it to cool, and water your plants with it! The water becomes enriched with calcium as the eggs cook. Calcium is one of the macronutrients. It strengthens cell walls of the plant, and helps with mineral transport in and out of cells. Just remember to allow the water to cool first, and don’t add salt to the water as you’re boiling.

The post was followed by largely positive comments of people willing to give it a go. Why not? The boiled water would only go down the sink anyway.

But there was something about the claim that aroused my suspicion. Call it geeky intuition.

So, I contacted The Garden Professors via their Facebook page. These are four helpful and knowledgeable US urban horticulturalists who advise plant lovers on evidence-based gardening. They’ve also recently revamped their blog.

So, what did one of the professors, Associate Professor Linda Chalker-Scott, have to say about this eggy gardening tip?

Unless you are boiling the eggs in vinegar or some other highly acidic liquid, calcium is not going to be released from the eggshell. It’s in the form of calcium carbonate, which can be dissolved in acid.

In other words, unless you boil your eggs in acid, the calcium will remain fixed in the eggshell and won’t end up in the water.

While Linda talks about adding vinegar to the boiling water to release the calcium, I take it she’s not advocating you pour acidified boiled egg water onto your plants, as this can kill them.

Don’t ask me how much you need to dilute the vinegar to find that perfect balance – enough to release the calcium into the egg water but not enough to kill the plants you’re trying to feed. I’m sure there’s a neat school project in there somewhere. Any takers?

So, the upshot is this. Sorry Austraflora and other circulators of this common garden myth. Pouring egg water around your plants generally won’t give them a calcium boost.