Gnats on Houseplants


I recently purchased four beautiful Massangeana Cane plants from Lowe's and some good potting soil. I potted my plants in nice planters and within a week there are millions of gnats crawling out of the soil and flying everywhere. I just purchased Knock-Out Gnat from and waiting for its arrival. Hopefully it works but in the meantime, is there anything I can do to get rid of these pests?

Madi from Oceanside, CA


Almost everyone who grows houseplants has experienced these little black gnats. They are called fungus gnats. They inhabit the fungus and decaying plant material found at the base of houseplants. The fungus gnat's lifespan is as follows:

Adults live about 7 to 10 days and deposit eggs on or in moist soil. The females lay from 100 to 300 eggs in batches of 2 to 30 each in soil containing decaying organic matter. The eggs hatch in 4 to 6 days and the larvae feed for 12 to 14 days. The pupal stage is about 5 to 6 days before adults emerge. Repeat.

The adult gnats are an annoyance, but they won't hurt your plants. The larvae, however, can damage the feeder roots and root hair causing a general loss of vigor to some plants. The best way to prevent fungus gnats is to use a sterile potting soil mix when re-potting (one that is free of bark chips) and to make sure your pots have good drainage. These guys need a moist environment to feed and continue breeding. So if possible, it's a good idea to let the surface of the soil dry out as much as you can (without injuring the plants) between watering. This works well to kill the larvae.

Here are some other things to try:

  • Be sure to practice good sanitation by removing any dead plant material and debris from the base of your new plants.

  • Replace the top few inches of soil with a sterilized potting mix.

  • Place yellow sticky traps near your plants to monitor the population and nab flying adults.

  • Use a fine peat moss on top of your potting soil to deter the gnats.

  • Place 1/2 inch slices of raw potato on the surface of the soil and discard (along with the larvae) after 2 days. Repeat until larvae are gone.

  • Place red cooking wine or fruit juice in glass and leave it out by your plants. Adults will dive in and drown.


Gnats on Houseplants


Use any type of lemon scented spray. I use lemon scented ammonia. Wipe down the area with the lemon scented ammonia or spray the area. You will notice there are very little or no gnats at all instantly. (06/30/2008)

By tonyaphl

Gnats on Houseplants

Don't pour coffee into the soil anymore. You can pour it outside. Also for others, only put coffee grounds into a compost bin and not directly around plants. (06/30/2008)

By OhioGirl

Gnats on Houseplants

I just mix up some soap water in a spray bottle to get rid of the gnats. (07/01/2008)

By Joyce

Gnats on Houseplants

Don't know about the gnats. Scooping the top layer and replacing it with some of that baked soil sounds good. But the roaches...Boric acid will kill them. Put it into crevices or sprinkle it around the cutouts of pipes under the sink or wherever you think that they come in. It doesn't lose its efficacy, so will last as long as they walk across it, then groom themselves. Your roach problem will disappear. Put a straw near the openings if they are small and blow some of the Boric acid into the hole or crevice. (07/01/2008)

By Thrifty Me

Gnats in drains

Pour a little salt and a some of baking soda down the drain. Then pour white vinegar. Let it fizz overnight. Follow the next morning with boiling water. If this doesn't work, the drains may have something in there that needs to be cleaned out. Then try the process again. It absolutely works! We had a million and they're gone! (07/11/2008)

By Shannon

Gnats on Houseplants

I have had them from time to time. I don't know how you feel about Raid or any other house bug spray. But, when I do get them, I take the plant out doors in the morning, spray the top soil really well and let it sit outside for the rest of the day. If it's too cold at night to leave it for another day, I usually put it where my washer and dryer are for at least another day. Then move it back. It always kills every part of the life cycle. (08/29/2008)

By Chris

Gnats on Houseplants

River city, wickedly humid. I've used diatomaceous earth (D.E.) with lasting success for some time. Think of it like inhaling powdered glass, sprinkling powdered glass on your corn flakes.

Not very 'humane', but it does make short shrift of the little vermin. For my indoor trees, Potassium permanganate ( @pharmacist: It's for my citrus plants! Would this face lie? ) kills fungus. Soil fungus+Trees in poor soil=good thing --usually, but I do use it on plants subject to root-rot, once in a while. It's inexpensive, very little is needed and it works fast. And environmentally safer than detergents when used on its own. No household cleaners, bleach.

On the other hand, D.E. is excellent on orchids, since their fungal 'partner' is selective, and vital. Potassium permanganate breaks down quickly into non-toxic salts, utilized in by the plant.(as Na, oxides) -- Not for foliage.

Soap: mycelium (living fungus) is usually a waxy/greasy kind of business in peat, soaps like 'Safers' are OK for control. I've used dish soap which is a little harder-hitting. Problem is that permanganate soaps really aren't very picky, and most fungi, even if they're not feeding the plant directly, help keep clean water in the soil. Bacteria, small insects, fungus are all fair game to detergents.

D.E. doesn't change soil Ph. It is inert, like sand, only much finer. Neighbours with houseplants. That neighbour you just can not relate to? Just because gnats can't spawn in your pots anymore, that won't keep them from trying. And I guess it wouldn't be 'acceptable behaviour' to sticky-trap a few doors and windows shut. What-to-do. Or maybe it's just this darn humidity. Maybe gnats would go away on their own, or maybe green thumbs just wouldn't be as irritable. Thanks for some good tips posted, happy hunting!



By some guy from Edmonton

Gnats on Houseplants

We just had this problem, I bought my dad house plants for Christmas, completely re-did his living room. It looked great, until we started getting gnats everywhere. Thank you everyone for letting me know what was doing it, we just put our plants outside and will be working on DE-GNATTING them.

Here's some advice for those of you with gas heaters. We have several gas heaters, and since it's winter time we've been using them. I noticed today while turning one on about 16 gnats dead on top of it. On the ground underneath it were tons more dead gnats. So we have our own gnat killers. We're trying the ACV trick too, just to make sure. (02/08/2009)

By Mehoni

Gnats on Houseplants

Windex. You'll have little gnat bodies everywhere. (02/13/2009)

By Paiz


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