How to Use Diatomaceous Earth On Houseplants

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I’ve known about the existence of diatomaceous earth for a while ( I watched a Betsey Begonia video on it), and I thought it ‘d be a great topic to read up on and write a blog post about, since it’s one of the most effective ways of getting rid of fungus gnats.

So I innocently googled ‘diatomaceous earth’.



I will NEVER not be shocked by the things seemingly normal people eat but I was a bit taken aback. It’s literally fossils.

Full disclosure, I didn’t read about the benefits of eating diatomaceous earth. I suspect it’s the apple cider vinegar gang, and I’m likely to be sucked in. I currently don’t have the funds or the time to devote to a diatomaceous earth diet.

By the way, I’m not an apple cider vinegar denier. I’m just jealous because I can’t stomach it.

Anyway. We’re here to talk about the benefits of diatomaceous earth with regards to house plants, not constipation (ok, I researched a little bit).

What is diatomaceous earth?

Diatomaceous earth is white, crumbly rock, made up of the fossilised remains of diatoms (wait, can vegans even eat this?)

Diatoms are algae (yes, they can!) and they’re…pretty spectacular. Not only do they make up a decent proportion of the earth’s biomass, but they produce 20-50% of its oxygen.

Which I suppose isn’t that surprising since there’s so many of them, but still. Thanks, guys.

The ocean floor is sometimes as much as half a mile deep in the shells of dead diatoms (I’m a little confused as to why microalgae have shells).

Fun diatomaceous earth fact lifted straight from Wikipedia: winds from the Sahara blow 27 million tonnes of diatomaceous earth over to Amazon, where it fertilses the ENTIRE Amazon basin.


Diatomaceous earth is used in toothpaste, cat litter, thermal insulators, and an activator in blood clotting studies.

I defy to find a more diverse set of uses.

Why do people use diatomaceous earth in house plants?

There three main reasons that diatomaceous earth is a useful product for indoor plant lovers.

1 – As an insecticide

This is probably the main reason plant owners add diatomaceous to their soil. It’s a mechanical insecticide, so rather than poisoning pests, it dehydrates them.

It is also extremely sharp if you’re a pest larva, and physically kills larva in the soil before they can emerge.

2 – It improves drainage

Diatomaceous earth can hold up to four times its own weight in water, so is popular in cactus and bonsai soil mixes.

It retains water and nutrients while allowing water to drain freely and quickly.

3 – It can help deter mould

You know that white mould that sometimes grows on the top of your soil? It’s a mould that pretty harmless to your plants but doesn’t look…great.

The dehydrating properties of diatomaceous earth can help reduce surface mould, and soil moisture, which in turn can deter pests like fungus gnats

Is diatomaceous earth an effective insecticide?

Yes – diatomaceous earth is a very effective insecticide for some pests, because it puts a stop to the whole lifecycle.

Fungus gnats, which lay their eggs in the soil, can’t physically lay their eggs if there is any diatomaceous earth present, because it dehydrates and kills them on contact. If you add DE after they’ve laid their eggs, then the larvae are killed when they start to emerge.

That being said, not all pests lay their eggs in the soil. Spider mites, the bane of most plant lover’s lives, lay their eggs on the undersides of leaves, so diatomaceous earth is unlikely to be effective against them.

If you have problems with gnats, flies, roaches, or silverfish, diatomaceous earth will definitely help, but spider mites, thrips, scale, and aphids are unlikely to be affected.

Damn. That’s really the only pests I get.

Technically, I could use it on the slugs that sometimes come into the kitchen but since apparently it’s like jagged glass to them, and they’ve never done anything to hurt me, I won’t.

How long does it take for diatomaceous earth to affect your plants?

It’s effective almost immediately, since it dehydrates bugs and soil on contact. HOWEVER diatomaceous earth is a very fine powder, so it could potentially get washed away when you water.

Some people say it’s ineffective when it’s wet, some people say it’s better, so I suppose it’s a matter of trial and error. Still, if fungus gnats are getting you down, this seems to be the way to get rid once and for all.

Where can you get diatomaceous earth?

Garden centres sell it, but I would recommend getting the food-grade stuff from Amazon, just in case you’re either tempted to try it OR (more likely) you have pets that like to eat soil.

It’s pretty cheap, and you only need to add a sprinkle to the top of each of your plants.

What else can you use diatomaceous earth for?

  • Getting rid of most pests that go near the soil. Apparently it even deters rodents.
  • Making explosives, should you need to
  • Filtration medium
  • polishing metal
  • Homemade toothpaste – I don’t recommend doing this tbh, unless you know what you’re doing. No one likes cavities
  • Deworming cattle
  • Anti-caking agent in grain storage
  • Growing medium for hydroponics systems
  • Deodorant
  • ‘Detoxifying’ the body. Don’t these people have livers? We have a whole-ass organ (and a massive one at that) for detoxifying our body.

I’m going to stop there, because I keep coming across articles that claim that diatomaceous earth kills cancer and prevent diabetes and alzheimers, and we’re here to talk about plants, and how to get flies out of your wine glass, not cure dementia.

Are there any negative side effects of using diatomaceous earth?

  • It’s very fine powder and can irritate the lungs, so wear a mask. Avoid if you’re asthmatic, just in case
  • It has to be kept dry to be most effective, so maybe less effective on Calathea and ferns

Do I use diatomaceous earth?

No. I don’t have that much of an issue with gnats. I prefer to practice preventative care when it comes to plants, so I clean them with neem oil, which gets rid of a wider range of pests.

I’ve seen a lot of people top dress their plants with regular sand, which is cheaper than diatomaceous earth, and is less likely to get into your lungs. It’s a pretty effective way to deter fungus gnats, though admittedly it’s slower to get to work.

Caroline Cocker

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

18 thoughts on “How to Use Diatomaceous Earth On Houseplants”

  1. Thanks so much for this article. I didn’t know how to use it but now I do. You have been very helpful to me.

  2. I move my houseplants to the screened porch in summer. When I get ready to bring them back inside in the fall, I have collected a few roaches. I’m wondering if diatomaceous earth could be the magic answer for deterring the roaches from camping out in my plants?

  3. It should get rid of them – I don’t want to make any promises because roaches are really resistant, but it should work.

    Just make sure the diatomaceous earth is kept dry, so bottom water if you can.

  4. I love that you warn people not to make homemade toothpaste with diatomaceous earth but no warning on the homemade explosives 😀

  5. The problem with DE is that it doesn’t work if it’s wet – a fungicide might work, or flushing the plant with diluted hydrogen peroxide

  6. Not even overwatering my plant, I have used diatomaceous earth on my plants because of a fungus gnat infestation (and also because of some mysteriously appearing centipedes and tiger worms in the plant pots next to my bed which I don’t want to think about anymore). It worked really well, but now I seem to have a problem with water retention in the soil. It looks like the plant roots are not able to absorb anything anymore and are slowly suffocating. I mean, my spider plants died, which is close to impossible. Repotting will be done in spring, but just wondering if you have any thoughts on this 🙂

    On the topic of cockroaches: to my understanding DE o works best on soft bodied insects, the hard shelled ones are more protected from dehydration.

  7. That’s a really good point – I suppose maybe it can act like sand and increase drainage. My advice would be to bottom water your plants and let them soak so they can absorb as much as they need, and it’ll avoid washing the DE further into the pot.

    Also, I cannot keep a spider plant alive, so it’s absolutely not impossible. Well, it’s not actually dead, but it’s just a collection of (very healthy) roots. No leaves. They just brown and shrivel. It’s currently in Leca awaiting spring.

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