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Why are my indoor plants growing mould?

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If there is mould growing on the surface of your plant’s soil, DON’T WORRY.

Chance are, it isn’t doing any harm. It’s a really common occurrence, especially if you have moist soil. However it can point to underlying issues.

Let’s best honest, it’s probably an overwatering issue.

Oh, before deciding your plant has mould, be sure to rule out mealybugs. They do look a bit like mould, but the, er, bugs is what distinguishes them from actual mould.

What causes indoor plants to grow mould?

The mould growing on the soil of your plants is most likely to be saprophytic fungi. It feeds on decaying organic matter in moist soil so it’ll urn up if:

  • You don’t remove dead leaves from the surface of the soil

  • You’re using DIY organic fertilisers wrong – you can’t just lie a banana skin on top of the soil and hope for the best

  • You’re not letting the surface of the soil dry out properly before watering again.

  • The fungus will attract fungus gnats. And whilst fungus gnats aren’t usually too much of an issue, an infestation can be a problem. The larvae can end up eating your plant’s roots. And say goodbye to eating without a fly trying to get into your mouth.

I’M A VEGAN, HAVE SOME RESPECT, FLY.

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What kind of mould grows on house plants?

It’s most likely that your plant has white mould – the saprophytic fungus I mentioned before.

Plants can also have black mould, sooty mould, grey mould, or powdery mildew.

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Should I be worried about the mould harming my plants?

It really depends on the type of mould you’re dealing with. If you just have white mould on the soil, it won’t harm your plants – it just wants to eat decaying matter.

That being said, mould turning up can be a sign that something is wrong – I would gently ease your plant out of its pot and check the roots for root rot.

Constantly moist soil is a sign of overwatering, and if you’ve been overwatering for so long that mould’s moved in, you’re well on the way to root rot.

Overwatering is a curse, so I’ve written a post on how to stop doing it.

There are other moulds that can harm your plant though, for example, sooty mould deposits that are a sign that your plant is infested with scale, so watch out for that. Scale is a bitch.

Powdery mildew is also…not good, and can kill your plant. It looks like a white powdery film over your plants, and covers the leaves, inhibiting photosynthesis and causing stunted growth, or even death.

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Is the mould growing on my plants harmful to humans or animals?

No. But be sure to wash your hands after treating it, because you don’t want to inadvertently spread it to your other plants.

Also, maybe don’t let your pet and kids near it. I can’t find anything to suggest it’s harmful, but still. Let’s not take risks.

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How can I stop mould growing on my plants?

Preventative care:

  • Check your plants for mould when you buy them
  • Make sure the top of the soil gets chance to dry out between waterings. Even moisture-lovers like Calathea. Even if the top of the soil is dry, the layers underneath can still be damp.
  • Keep a close eye on your plants – aim to check them over a few times a month.
  • Remove dead leaves from the soil
  • Take good care of your plants – make sure they have enough light, aren’t over watered, and are in a pot that has drainage holes.

How to get rid of mould:

Firstly, isolate your plat so it doesn’t pass it’s mould on to any of your other plants.

  • If it’s regular white mould, you can just scrape it off the soil with a weapon of your choice – let me recommend a spoon.
  • If it’s warm outside, take your plant out to help it dry out more quickly. Be careful not to leave it in direct sunlight – we don’t want it to cook
  • I’m gonna mention neem oil for the billionth time – it’s a great fungicide, so spray your plants with a neem oil solution – be sure to dry them with a cloth or kitchen paper after
  • Repot your plant in sterile soil
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If you have any more mould-related queries (or information) be sure to leave them in the comments.

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