One of the drawbacks to moving plants indoors for the winter is that they bring their friends with them. You find a sunny nook for the plant to enjoy, coddle it for a few months, watering or giving it the odd shot of fertilizer. Everything’s fine.
But then odd things begin in other areas of the home. At first, one or two tiny flies wing lazily through the house. No big deal, you ignore them. But they meet, go out for a few drinks and woo one another until suddenly, you’re playing host to a brood of fungus gnats.
They gather around the plants, partying and procreating, fly around computer screens as if it contains the Wisdom of Solomon, and explore faces and nostrils in a quest for glory. You play dumb when guests visit, vainly hoping the gnats won’t make an appearance, but they do. You can always tell – your guests are flailing at the air when they think you’re not looking.
It’s time for biological warfare. But first, a bit on fungus gnats, so you know your enemy. Contrary to popular myth, they don’t spring from the dust of plants in spontaneous generation. They’re native to our area and find their way to potted plants spending summer outdoors. Fungus gnats lay eggs in the soil and once hatched the larvae (maggots, but who wants to know that) graze on fungi in the dirt, or nibble on the fine roots of the plant.
Experts may tell us they don’t harm the plant, and this is true, but they annoy the heck out of us. Get a grip on your gnats by:
– Find the mother ship by placing a slice of raw potato on the soil surface for approx. 4 hours. This gives your guests something to talk about other than your cooking. Turn the potato over and look for the maggots – they’re creamy white with a shiny black head.
– Once you’ve found the culprits, several choices for weaponry can be had. You could go with parasitic nematodes or predatory mites which are introduced inside your home to hunt down, kill, and eat your gnats in a gruesome enactment of the wild kingdom. For my money, I don’t want anything that, should it polish off the last of the gnats, come looking for me.
– Azadirachtin, a growth regulator that comes from the neem plant. Essentially, this makes it impossible for the bug to molt one it’s gotten too large for its skin. Anyone who’s put on a few pounds over winter can relate – nothing fits. But this may be hard for homeowners to find.
– Bacillius thuringiensis, strain isrealiensis. This is a bacteria found in soil that attacks the second stomach of the insect (they have three), tearing it apart with a protein crystal that acts a lot like those wicked pickled eggs I had at a bar in Des Moines one year. This is a great choice. Look for Knock Out Gnats on line, or if you’re lucky and live in Boulder, check out a little greenhouse supply store in Gunbarrel called Way To Grow. They have small bottles of Gnatrol, a Bt that you can mix up with water and pour on the soil.
Gardening after five 
Thanks so much for this info…these little things made their way into the house a year ago and my husband blamed their presence on an orange tree I got…might have been, but I suspected my container plants that I try to keep going over the winter. This year they haven’t been as bad…I think because I left my containers out a little longer in the colder evenings and nights before hauling them in. But there has been enough of a hatch that one seems to be present almost every evening by the lamp near the chair my husband sits in. The evenings are punctuated with outbursts of profanity and much swatting of a rolled up paper!
Thanks for the chuckle, Joan. Since the fungus gnats keep hovering near your spouse, have you considered placing the slice of raw potato on his head to see if he’s the mother ship for them?