Sand gnats in houseplants, help!

[Mrsbrownsbuoys]

I've got lots of new cuttings and established houseplants and noticed a week or so ago there are what I believe are called sand gnats flying around and crawling on the soil.

Has anyone successfully got rid of them? And how?

I've put a jam jar lid with honey to catch them next to the plants which has caught a few. I've stopped watering the plants because I read the gnats need moist soil to lay eggs, but now the cuttings are drooping a bit and I've had to tentatively water them.

Anything I can treat them with? Preferably not pesticide, but I'm reaching the point where I will if I have to.

TIA

Actually I think they're called fungus gnats

The problem is they’re hatching out from little transparent larvae which are voracious eaters of fat plant roots. So the first thing to do is to have all the plants out of their pots and check for larvae. Consider repotting in new clean soil.

Once that’s done, it’s a matter of prevention. They like humus rich soil, so you need to convince them the soil isn’t like that. A layer of gravel or grit on top of the soil does that.

It’s not instant, but if you put gravel round everything, after a few years you’ll realise you haven’t had an trouble for years.

The gnats can be killed by ordinary indoor fly spray, or by squishing by hand as they crawl round the edges. But it’s the larvae which are your big problem.

Thank you. I've just spent all afternoon repotting some of them. I've covered the soil with gravel. I couldn't see any larvae but I've rinsed off most of the old soil, washed out the pots, so hopefully it'll help. I've still lots to repot though.

Also, not overwatering helps. They love moist soil.

Thanks. I've been trying to do that, but worry that my cuttings are too dry.

I got rid by -
Watering less often and only ever from the bottom.
Repotting carefully with clean new soil and raising the top level a little higher than original.
Layer of fine gravel on top.
I did also use a spray but only once as I was worried about it killing the plants (young and tender). I actually think this may have worked. But still have none after around 6 months so all other steps helped to keep them free of them I think.

@Mrsbrownsbuoys

Thanks. I've been trying to do that, but worry that my cuttings are too dry.

Use a more gritty compost for your cuttings

Thanks both.

Nematodes!

You can buy them online, you mix them into water, and they kill off the larvae in the soil. Very eco friendly.

I've not heard of them! Will they multiply too and wander around my house? Do they damage the plants at all?

Nematodes are everywhere already. A former colleague of mine, a nematode taxonomist, claimed that if everything in the world was evaporated apart from the nematodes, it would look no different, because everything would be outlined by the nematodes.

They have different mouth parts depending on what they eat. So you can be assured that nematodes with meat eating mouth parts and a taste for fungus gnat larvae will not start chomping on your plants.

Wow! Thanks. I'll look them up.