Here’s Why There’s Mould Growing On Your LECA

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I’m foolishly writing this in summer when I don’t have any mould on my leca, but I often do and other than being gross, it’s not a big deal.

Check that it is mould

Mould on leca tends to look like fine grey-ish hairs, and it’s soft and, er, looks like mould.

If you have white crystals on the top that are crunchy and disappear when you pour water over them*, then that’s just a build-up of mineral deposits.

This is a perfectly normal part of keeping plants in leca. The leca gets damp, and then the top dries off, leaving behind anything that was previously dissolved in the water. It could be from the fertiliser, or just from your water but it’s one of those things that would be weird if it wasn’t happening*.

Ideally, you should be flushing your plants monthly and stopping the mineral deposits from building up too much.

Whilst they’re not necessarily dangerous, they can mess up the pH of your nutrient water and cause nutrient lockout which…as well as causing nutrient deficiencies in your plants make the whole process of making up the nutrient solution pointless. As a lazy person, this is unforgivable.

I don’t actually flush my nutrients (this is the paradox of the lazy person!) but I do make a point of purposefully washing off the mineral deposits on my leca when I water them. Then I dump the mineral-filled reservoir into another plant (I switch it up to keep things fair) and fill the reservoir with fresh nutrient water.

I’ve taken to watering all my plants in my weekly watering session with nutrient water. Some plants need top-ups during the week which I do with plain tap water.

*Annoyingly, after being more consistent with my watering, there is no buildup on my leca anymore.

If you don’t flush for a while, the buildup refuses to shift.

I don’t think this is a problem, because it’s basically solidified and won’t leak into the water (honestly I have no idea if this is true, but I’ve never had an issue).

I also thought it was here to stay forever, but when i went to take a photo of it, it was freaking GONE. Rude.

Why is there mould on my LECA?

Mould grows in damp places, and leca is damp. It doesn’t hurt that there’s a reservoir of nutrient water right near it to keep it fed.

Is mouldy leca harmful?

Mould of leca looks grim af but it’s not necessarily a problem.


(there’s always a however)

Mould growing on leca could be a sign that there isn’t adequate air low around your plant. It can also be a sign that your plant is too cold, or that something is contaminating the system – usually if you haven’t cleaned soil off the roots well enough.

I had a quick Google of mouldy leca and a LOT of people were saying that if you have mould on your leca then your plant is doomed and you have to get your leca into the sea.

In my experience, nothing bad happened when I had mouldy leca. From what I can tell, my issue was that my room was too cold and humid, and mould grew o the top of the leca.

My plant was fine and is still with us now. it looked a bit sad at the time, but that was more likely because it was winter, not because it had mould.

If anyone has lost a plant to suspected mould, let me know – I’m not saying it doesn’t happen, just that it didn’t to me.

How to get rid of mould on my leca

I just flushed the leca through with tap water and moved the plant to a warmer spot. I didn’t put a fan on to help with airflow, but that’s definitely an option.

The best thing you can do is put everything in place to help your plant grow better. Better light, balance warmth and humidity (a heat mat can help in winter) and keeping the leaves dust and pest free.

Not only will this help the plant if the mould does have a negative effect on it, but it will also reduce the nutrients in the solution (because the plant will grow through more if it’s growing faster) which are helping feed the mould.

If you want to take everything apart and boil the leca (which is what Reddit suggested) you can, but I personally don’t think it’s necessary.

Final thoughts

Mould on your leca is a sign that the environment is too humid, potentially too cold, and doesn’t have enough airflow. Whilst these things can be harmful, the mould itself is unlikely to be. Take it as a sign to adjust the temp/humidity/airflow.

Caroline Cocker

Caroline is the founder and writer (and plant keeper) of Planet Houseplant

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