Gnats in Potting Soil

How do I get rid of household gnats in potting soil?

By Tammy from VT


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January 28, 20100 found this helpful

I have this problem no matter how many times I've changed the soil. I have no solution as of this date.

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January 28, 20101 found this helpful

After you repot in clean soil, you might add a thin layer of sand to help keep them from getting to the potting soil. Best to use a growing sand that will be salt free.. a fast remedy is to mix up any liquid insecticide that is safe for the plant, even diluted down a couple of times and then use this mixture to water the plant, this will kill the larvae in the wet soil. There is also a product called Gnatrol you can use. It is Bt and only effects the larval stage so is slower to gain control.

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January 29, 20100 found this helpful

Those are fungus gnats, and they are difficult to get rid of completely. Thankfully they seldom really harm the plants, though they are a real nuisance. In addition to the tips below, hanging a sticky fly strip near your plants will trap a lot of them. Another tip I have seen is to put raw potato cubes near your plants and change them every three days.


I think they are supposed to lay their eggs there instead of in the soil. (The worst infestation I ever had was when I had a 50 lb bag of potatoes near my plant lights in the basement, and there was a bad potato near the bottom that I didn't find for some time, so I guess they really like potatoes.)

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February 7, 20100 found this helpful

I was looking for a solution to my gnat problem. I opened a brand new bag of potting soil for some seedlings, and gnats came swarming out of the bag. I talked to my Aunt who has worked at a florist for years and said they microwave their soil for a few minutes and let it cool down before planting. It kills the larvae. Be careful, microwaving for too long can cause the soil to catch fire. Also the house will get a woodsy smell to it after doing this, she suggested microwaving some lemon juice to get rid of the smell.

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November 20, 20101 found this helpful

First I soak planters in mild chlorine bleach then rinse. This water is poured over the gravel walk behind house and kills the moss/mold on pavement. We have plants lining walk and this has never bothered plants.


I have problems with soil gnats every year when I bring my household plants back into house after they've lived outside, plus, I have 3 cats. Finally found a solution ~5 yrs ago and works every time.

After repotting, add a thin layer of larger particle activated charcoal (can get at pet/fish shop) just on top of the soil. I then cover this with plastic mulch - some colors like blue or yellow enhance the colors of the plant. My favorite is blue, the green plants and/or pink blooms seem more vibrant.

The charcoal takes care of the gnats (as I've read they like moist soil) and the cats won't disturb the plastic mulch. If you have really large planters, I'd try the volcanic rocks that you might use for landscaping or grills. Had these in some really large planters with taller inside bushes. Cat could get into planter, but, jumped out quickly when she touched the rock.
Happy indoor planting !!

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