Five tips for dealing with fungus gnats

Fungus gnats. Sciarid flies. Houseplant flies. Or as I like to call them, The Flies We Love To Hate. When it comes to pests, fungus gnats are probably public enemy number one as far as houseplant growers are concerned.

And yet they don't actually do that much harm to our plants: they just annoy the heck out of us. I revisited an early episode from the On The Ledge archive last week, bringing you a whole heap of useful information about fungus gnats: you can listen here. And when you signed up for this newsletter you should have received my in-depth PDF guide to fungus gnats: if you have mislaid it drop me a line and I can get a copy to you.

In the meantime, here are five helpful tips:

Sticky traps are a useful way to monitor an infestation, but most likely won't completely cure the problem. They are yellow as this colour attracts the adult flies: if you buy traps with a grid pattern, replace the traps weekly and you can ocunt how many flies have been caught per grid square and see if the infestation is improving.

If you've wondered how to tell a fungus gnat from a fruit fly: fungus gnats are black rather than brown, and slightly smaller (2mm-4mm long) and more 'wafty' (not a technical term but you know what I mean). Fungus gnats look like a shrunken mosquito while fruit flies look like teeny tiny bumblebees.

Fungus gnat infestations are at their worst at two points in the year: spring and late summer/early autumn, so now is a great time to get your defences ready. 

Don't waste your time repotting all your plants if you have fungus gnats. Potting soil will soon by reinfected by the female adult flies which will lay more eggs. 

If you like to take a natural approach (AND have an excuse to buy another plant...) butterworts (aka Pinguicula) and sundews (Drosera species) are two types of carnivorous plants that can help to control fungus gnat numbers. Do your research before buying, though, as they have different care needs to most other houseplants - for instance, they must be watered with rainwater, and they need loads of sunlight.

This blogpost was taken from The Plant Ledger, my email newsletter about the houseplant scene. Subscribe here and get my free in-depth guide to fungus gnats.