Would sand on soil harm houseplants?

[teaandcake246]

There are fruit flies or fungus gnats in my flat, presumably living in the soil of my houseplants. (The flies arrived with plants I bought online.) I have put pebbles on the soil, but I’ve seen flies climbing in and out through the pebbles. I’ve made a trap with cider vinegar, but the flies ignore it. I’ve tried sticky yellow traps, and the flies ignore those too. I’m wondering whether to put sand on the soil, to prevent flies reaching it and larvae getting out, but if I do that, then when I water the plants sand will gradually seep down and mingle with the soil. (I have to water from the top because of how the pots are.) Do you think it would harm the plants to have sand mixed in with the soil? (I don’t know whether the soil would then not be properly aerated, and whether that would matter!)

Also, does anyone have any other ideas for his to get rid of these flies, please?!

Thank you!

[BrigidSt]

Let the top inch or so dry out in between waterings, the fly maggots die off. They like it damp and live in the top layer, so dont keep it totally moist all the time.

[BumblebeePlantMum]

What plants do you have? If they are cactus or succulents, have a poke of your actual plant to make sure that it isnt rotten. Fruit flies love a bit of rotten cactus, and the way succulents are, they often look healthy at the top for a while when it is all going manky down below.

Sand won't damage your plants though, as long as it is clean and not salty from the beach.

[teaandcake246]

Thank you very much for the replies. I have tried letting the plants dry out as much as possible in between waterings, but it got to the point where the plants were starting to suffer from lack of water, and the flies were not gone.

Three of my plants are succulents (string of hearts), so I will check those for rot - thank you. (Two of them are new, so I hope they’re not rotting!) My other plants are: ivy, kentia palm, parlour palm, pony tail palm, spider plants and sweetheart plants.

Diatomaceous earth and horticultural grit sound like great ideas - thank you!

[MereDintofPandiculation]

Possibly waiting till the growing season has really started, I would repot all your plants, checking for any larvae.

Sand works, but gets displaced when you pour a stream of water on to it, so although I used sand when there's nothing else available, I find grit is better.

Thinking about it, they'll ignore sticky yellow traps because they're not after leaves (the yellow traps are designed mainly for whitefly who seek out new growth), but I wonder whether an ordinary brown flypaper would work? Cut into smaller pieces and placed down at pot level.

[teaandcake246]

Those are good ideas - thank you.

[BrigidSt]

Yeah, its not a total solution drying out between watering. Perhaps remove the top layer of compost, like if you're top dressing, get rid of the eggs and maggots that way, let it dry out, replace with fresh clean compost? Some of my plants are old, its chronic. Also I disturb the soil surface if I"m hoovering in that room and stand and wait, suck them up without hopefully damaging the leaves. Or the same scurrying the soil up and try and squash them clapping them. Lower the population. Sounds bonkers but its satisfying if you get a few. I also tried vinegar traps or wine, didn't work really. The only chemical treatment is the same as for vine weevils, youd have to water it on and that seems a bit much for indoor plants.

[MereDintofPandiculation]

The only chemical treatment is the same as for vine weevils, youd have to water it on and that seems a bit much for indoor plants. You can get rid of the flies with ordinary indoor fly killer. So if you can physically get rid of the grubs, kill off the adult females, and deter any you miss from laying because your pots look like a humus-less gravel heap, you can get it under control.