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by Sonya
(Toronto, Ontario)

I am having major issues with fungus gnats – is there no way of controlling these horrible little insects? I’ve tried repotting my whole collection (that was during the summer and it’s now winter) but they are back! I vacuum them, swat them, smear them into the window, and I can’t seem to lower their numbers at all. Just when I think I’ve finally got them whipped, they come back even worse! Help!

Drought Smart Plants reply:

I feel your pain – fungus gnats are indeed a plague, what with flying up into your face when you water, and worse, eating the roots of your precious plants.

They can be beat with determination and patience. Here are a couple of other things to try:

Repot your plants into a well drained media, sterilized and without peat moss in it. The fungus gnats are attracted to damp soil, with organic matter in it to lay their eggs, so if there isn’t anything there for them, they’ll go elsewhere.

Put some kind of pebble or lava rock mulch on the top of the soil, which will make it more difficult for them to find the surface.

Don’t over water! I can’t stress this enough. Most houseplants are fine with a drying out period in between a thorough watering, which will make the soil less appealing to fungus gnats.

Yellow sticky traps work like a charm – they’re ugly, and messy but they are virtually fool proof. Hint: wet your fingers if you have to touch the sticky part, and the tangle foot won’t stick to you.

Three new methods that I haven’t had a chance to try (the sticky traps worked so well that I have no fungus gnats!):

Place four or five copper pennies at various places around the outside of the pot, just under the soil. Apparently, this sets up a slight electrical charge that the fungus gnats don’t like.

Water with a diluted solution of Hydrogen Peroxide to kill the larvae. The plant will love you for it, as this adds more oxygen to the soil.

Buy some special nematodes that will prey on the larvae.

Good luck with your war on these pesky little insects!