House plant flies

[KloppsTeeth]

I bought 5 plants from IKEA 10 days ago. Three succulents and two raindrop plants. Since then we have been noticing tiny black flies around the house. Thought it was something from the fields, but now think they are house plant gnats. Never had them before.
I’ve put sticky pads out to catch them, but I’m worried they will lay eggs in the soil of my other plants.
We must’ve killed 30 today. What do I need to do to get rid of them? I don’t know which plant they have come in on. I’m very new to house plants, I have a couple of snake plants and a caleathea. Will I have to bin the lot if it is too late to control the flies? Help!

I suffered with these on houseplants for ages and tried a few things but eventually found a very easy fix.

They’re called fungus gnats and they only survive in damp soil. So the simple answer is you let your plants dry out. Not enough to die, clearly! But really very dry. Then water sparsely and I would only water by standing in a saucer of water for the first couple of times afterwards as the gnats and their lavae are surprisingly near the surface.

Once you’re sure they’re gone you can resume watering as normal.

It works, 100%, and no need for chemicals or expense.

I agree with @Mykittensmittens, and I'd also take them out of their pots, scrape off and replace the top inch or so of soil.

If you have a persistent issue with fungus gnats the best solution is nematodes. I've found this to be most effective, though sticky lads and new compost helps.

I second the nematodes solution - I did this a couple of years ago when they were pretty bad and it definitely helped.

Now I also have one or two drosera plants around as well and they seem to help too - carnivorous plants which catch the flies! It's a natural way to control them and you get to own more plants

This is great news, thanks for this. I will give everything a try.

You can also try a few drops of washing up liquid mixed in the watering can when you water them. That can also be sprayed on.

Thanks @caranations

Yep washing up liquid in water helped cure our infestation!

Watching with interest. I recently bought a monstera from wilko and I have had some flies too, I think they came in with it. Have bought stones to put over the top of soil and sticky pads so fingers crossed.

the yellow sticky things help catch the adult ones. their maggots are in the compost chomping your plant's roots.
a thin layer of pebbles on top of the compost stops adult flies lying their eggs.

All my plants got the fungas gnats 3 years ago after a new plant purchase. I've tried every method mentioned on this thread - still have a few gnats but not many. All methods were partially effective and the sticky yellow things are doing a as great job. Bloody gnats.

Some great tips on this thread!

Do they bite?

They don’t bite. They just appear and hover about in the air.
Horrible things. The sticky pads are doing a good job. Have sprayed with washing up liquid water.
Going to buy some little pebbles to go on the soil.

One thing I used for greenfly was spraying the plant out of doors with insect spray then covering the soil with a layer of clingfilm. Tight round the stem. Left it on for a few weeks/month or two. It cleared up.

Usually the flies spend quite a bit of time walking up the outside of the pots, and they’re easy to squash.

Ordinary households fly spray will kill the flies. Then you need to repot the offending pots to get rid of any remaining grubs

If you don’t want to dry out your other plants, you can put a layerof fine gravel or sand on top-of the pot - the female fly will be looking for humus rich soil for her grubs

We’ve had loads too and still trying to get rid of them. Vinegar traps work to kill them too. I’m now only watering the big plants from the bottom. What nematodes do people use? I’ve tried mosquito dunks but didn’t work much. How much washing your liquid do you use?

Had these on our spider plants. I decided they were not worth the hassle and I got rid of the plants!

@purplesequins

the yellow sticky things help catch the adult ones. their maggots are in the compost chomping your plant's roots. a thin layer of pebbles on top of the compost stops adult flies lying their eggs.

Fungus gnat larvae are actually harmless, and feed only on decaying plant matter in the soil. They don't eat the living roots, just dead ones. That's according to the RHS website.

Ah, that's what they are! They're keeping my cats well entertained but thank you for the tips on how to get rid of them.

They are really annoying. We notice them more in the evenings and they just float into view. On a mission to get rid of them!

Fungus gnat larvae are actually harmless, and feed only on decaying plant matter in the soil. They don't eat the living roots, just dead ones. That's according to the RHS website. I’d agree they don’t eat fine roots. But when you have several plants with thick fleshy roots with soil full of mature fungus gnat larvae and roots cleanly nibbled off, and with nosign of any other pest, and several plants with intact fleshy roots and no fungus gnat larvae, it’s hard to come to any conclusion other than that fungus gnat larvae will eat thick fleshy roots.

When getting rid of the fungus gnat problem by applying a physical barrier (gravel) to the surface of the soil coincides with an elimination of the problem of having plants lose their roots, it just adds weight to the theory.

@MereDintofPandiculation

Fungus gnat larvae are actually harmless, and feed only on decaying plant matter in the soil. They don't eat the living roots, just dead ones. That's according to the RHS website. I’d agree they don’t eat fine roots. But when you have several plants with thick fleshy roots with soil full of mature fungus gnat larvae and roots cleanly nibbled off, and with nosign of any other pest, and several plants with intact fleshy roots and no fungus gnat larvae, it’s hard to come to any conclusion other than that fungus gnat larvae will eat thick fleshy roots.

When getting rid of the fungus gnat problem by applying a physical barrier (gravel) to the surface of the soil coincides with an elimination of the problem of having plants lose their roots, it just adds weight to the theory.

Ugh. That's some infestation there then. I can't say we've ever had anything more than a passing few, mostly coming into the house with pots of herbs from the supermarket.

I had this. I put layer of grit on top of the compost so they couldn't get to the soil and also put tiny saucers of orange squash in the pots and lots of the little flies jumped into the squash and drowned.