On a crowded windowsill, fungus gnats can soon spread to every plant
(view from an East Harlem brownstone window)
You go to water your plants and notice little gnats flying about. This can happen from overwatering or introducing an infested plant to the fold.
Isolating the problem plant(s) is the first step. The next important step is to cut back on water. Let the soil get dry in between watering. If it is a plant you love, you will not want to throw it away. The first popular solution is a bug spray, but even a 'botanical insecticide' can be harmful to humans and animals, especially when used indoors, and not easy to dispose of safely.
Molly Hackett of Victor, Montana, sent in a very safe and successful solution which was published in April's Horticulture Magazine: she uses sand.
Awesome advice...does this also work as a preventative measure?
Or is it only good when you have an infestation in progress?
For example, if you do it before the gnat larvae get deposited, will they still be able to survive if they burrow into the sand at the start?
view meltendo's profile
Wow, I was just about to write a comment asking about this - we seem to have gotten these little white speck looking flying bugs from a plant we bought at a farmers market, and now they're all over all our plants. We've been spraying with a vinegar mixture, which seems to agitate them, but hasn't really gotten rid of them. I'll definitely try the sand...thanks!
view Rosie's profile
I've had this problem with a few new plants I've gotten from nurseries. What has worked for me is to purchase nematodes from the nursery. It's a small sponge that contains the microscopic nematodes which you rinse into a large water container and water your plants with. The nemotodes eat the eggs. I still isolate the offending plant during this process.
view Sassy in SF's profile
Matt, very helpful tip. Thanks.
view gekko's profile
Thanks for the tip. I've recently seen gnats scatter on a planter I've been afraid I've been over-watering. One more indicator I should be sure to let it dry out between waterings. Many thanks.
view Doug's profile
I had this problem after re-potting some plants; I think there were bug eggs in the new potting soil. I went with the cheap, convenient, and highly effective method of spraying the plant with a mix of dishwashing liquid and water. Took care of the little bastards quickly and the plants showed no ill-effects whatsoever.
view Sydney's profile
Thanx Matt! Got little flying critters on the soil in my thyme and dill seedlings in my kitchen - horrible! Thanx to Sydney too, I'm going to try that cos it works on the aphids on my roses. If only you could train snails to eat them...!
view tin_angel's profile
Rosie,
The "white speck" bugs may be aphids. Try Sydney's method: dishwashing liquid and water in a spray bottle. Be sure to saturate everything, eve the under sides of the leaves. I'd repeat daily for 3 days and see what happens.
Soapy water is also supposed to be good to saturate the soil of your outside plants right before you bring them inside in the fall. Kills the bugs; or drives them out...
view Jon_B's profile