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Original poster

Fungus gnats

108 replies

CarterBeatsTheDevil · 09/10/2023 11:45

I've got a collection of cacti and succulents which I absolutely love and am very proud of. My husband has a rubber plant which developed fungus gnats (different room). He didn't want to treat them and now all the plants in my room (about 14) have fungus gnats. They all got them at about the same time so I didn't have time to isolate one in particular.

I know lots of people don't necessarily bother to treat them but when you have 14 infested plants that's a lot of tiny flies knocking around.

I've scattered diatomaceous earth in them and dried them out, but I couldn't leave them without water any longer (they'd been left for 4 weeks) and having watered them a week ago two of them are already showing signs of infestation again. They were very well drained. Is this just eggs from the last batch? Do I just keep going with the diatomaceous earth after every water?

OP posts:
Sleeplessinseattle234 · 09/10/2023 11:53

I had tons. So I re potted everything in new soil. Which was the thing that helped the most. After that I watered from underneath and I got those flower yellow sticky things. They are brilliant. They seem like a gimmick but they really work. Now a month later mine have gone.

Original poster
CarterBeatsTheDevil · 09/10/2023 12:29

I have been thinking about repotting everything - thanks!

OP posts:
dgirluk · 09/10/2023 12:36

I've also got this with succulents - I've put gravel on top which doesn't seem to have helped much - is DE a better bet?

Also just put those yellow sticky things out which have already captured quite a few flies, but def interested in any other advice :)

Original poster
CarterBeatsTheDevil · 09/10/2023 15:45

The DE works until you water, as far as I can work out, and then you have to sprinkle it again because it gets watered into the soil. I don't know if it's good for them to have repeated applications of it as it all gets washed into the soil.

OP posts:
Original poster
CarterBeatsTheDevil · 09/10/2023 15:45

I have tried the sticky yellow things and they are grimly satisfying but they don't deal with the BREEDING.

OP posts:
delishdelosh · 09/10/2023 15:47

You can buy nematodes which you water in to the soil, they feed on the larvae in the soil. Worked brilliantly for me previously.

gamerchick · 09/10/2023 15:47

Husband just uses normal fly spray on the plants, I wasn't sure but it hasn't harmed the plants at all.

I still won't do it myself like, he has to do the spraying.

Pilateshappy · 09/10/2023 16:07

I still have nightmares about when my plants got infested!

Weirdly the thing that worked the best was to buy a pack of small stones that you'd put in a fish tank and put a layer of them on top of the soil. Stops them getting into the soil and laying their eggs.

Begsthequestion · 09/10/2023 16:09

Organic liquid dish soap mixed in a water bottle and sprayed over the top surface soil can help.

ArseInTheCoOpWindow · 09/10/2023 16:43

CarterBeatsTheDevil · 09/10/2023 15:45

I have tried the sticky yellow things and they are grimly satisfying but they don't deal with the BREEDING.

How longs the breeding cycle? Don’t they just get less and less as more flies die?

And do you spray fly spray at the plant our the soil?

This thread is intriguing.

gamerchick · 09/10/2023 21:09

Both.

The tank gravel on the top can help but they just end up going under the pot and through the holes at the bottom depending on the pot. Little fuckers. scooping an inch of soil off the top can get rid of the babies as well.

But the raid does the best job. I've tried absolutely everything suggested apart from banned products.

Still not really comfortable with it. Just feels wrong.

A other way is not to water from the top, either water from the bottom or use a tube in a bottle of water for it to use like a straw. Let the top bit of the soil dry out.

Timewentfast · 09/10/2023 21:30

Yes I've had a problem with them this year. The most sucessful way to get rid of them I think is to stop watering them at the top and ONLY bottom water them. I also bought some sundew plants as they catch and eat the fungas gnats. I did have the sticky yellow things but had to keep replacing them so the sundew plants don't need replaced.

I tried the Sciarid Fly Killer Nematodes from Amazon which made a huge difference but unfortunately they came back. I suppose you only have to have one or two not killed out of thousands and they will start breeding again.

My recomendation is-

  1. Apply the Nematodes
  2. Bottom water only after that
  3. Buy a sundew to catch any remaining
Grushenka · 09/10/2023 21:38

I’ve had the sticky yellow things up for years - just two and they still kill even bluebottles. They’re great.

I had a major infestation from soil in my gecko tank. Every evening I left a tiny light on and hoovered them up. I had to go in every hour or so, and next to the light the wall would be crawling. It was the only way to get rid of infestation.

MereDintofPandiculation · 10/10/2023 09:53

You should take fungus gnats seriously if you have cacti, the thick roots of the cacti are loved by the fungus gnat grubs. Repot them all, taking care to remove any transparent grubs. Top the pot with gravel or horticultural grit to deter the females from laying eggs. Use a household fly spray on the adults. And tell your DH to sort out his hygiene.

Original poster
CarterBeatsTheDevil · 10/10/2023 22:49

MereDintofPandiculation · 10/10/2023 09:53

You should take fungus gnats seriously if you have cacti, the thick roots of the cacti are loved by the fungus gnat grubs. Repot them all, taking care to remove any transparent grubs. Top the pot with gravel or horticultural grit to deter the females from laying eggs. Use a household fly spray on the adults. And tell your DH to sort out his hygiene.

Oh god 😳 thanks. I was reluctant to repot now as it's getting colder but I'd be so sad to lose any of them.

OP posts:
MmePoppySeedDefage · 11/10/2023 05:25

I think I've mostly got rid using the yellow sticky things, one in each plant for a while, but I will try bottom watering too.

Almondmum · 11/10/2023 05:29

I've tried bottom watering, gravel and the sticky things. It's reduced them but not got rid of them completely so I've ordered the nemotodes. Fingers crossed that works because it's doing my head in. I'm also reluctant to report completely in case I kill the plants.

BooseysMom · 11/10/2023 05:35

Sleeplessinseattle234 · 09/10/2023 11:53

I had tons. So I re potted everything in new soil. Which was the thing that helped the most. After that I watered from underneath and I got those flower yellow sticky things. They are brilliant. They seem like a gimmick but they really work. Now a month later mine have gone.

Yes we got the sticky yellow things and they do work. We had hundreds which I reckon came from a bag of house plant compost as every plant I re-potted was infested in the little bds!! I put a yellow sticky thing in the pots and within a day they were covered in gnats. They do still fly around the house though and fly right into your mouth and up your nose! They like warm temperatures so the weather isn't helping get rid of them.

MereDintofPandiculation · 11/10/2023 11:24

CarterBeatsTheDevil · 10/10/2023 22:49

Oh god 😳 thanks. I was reluctant to repot now as it's getting colder but I'd be so sad to lose any of them.

Show quote history

Make sure the compost is not too wet for the cacti, and don’t water after repotting for about a month, then go back to winter watering regime.

Original poster
CarterBeatsTheDevil · 11/10/2023 15:22

Thanks. It's actually just one, as it turns out, which I've coralled. So I'll repot that one and keep it away from the others for a few weeks.

How does watering from the bottom work? Stick them in a tray of water?

OP posts:
Original poster
CarterBeatsTheDevil · 11/10/2023 15:23

(It was all of them, so I'm not ruling out that another few might turn out to be infested again as well.)

OP posts:
sunlovingcriminal · 11/10/2023 15:33

I use the yellow sticky things too- but the sodding little gnats still whizz about- and seem attracted to eyes and ears! Especially when watching telly. Or landing in my glass of wine!!

CrimsonElevenDelightPetrichor · 11/10/2023 15:38

I've tried:
Cinnamon
Fine gravel
Yellow sticky traps
Nematodes
Fly spray
Hydrogen peroxide
Drying them out & watering from the bottom

Nothing has completely got rid of them. I think fly spray is probably best, but I have an aquarium so it's a bit tricky. Hydrogen peroxide also works well, but it presumably kills off everything in the soil, which isn't ideal.

Billybagpuss · 11/10/2023 15:47

Carnivorous plants are the answer

drossera for the little gnat things. Saracenia and fly traps for the larger ones. They’re all fascinating and I’ve had no fly problems at all all year. I think the Saracenia are my favourites I’ve got quite a mixture of them.

RandomNutter · 11/10/2023 15:51

I've got rid of them completely just by using washing up liquid in the water.