I have a severe problem with gnats in my houseplants

[Ginevra]

I need ideas I haven’t tried. I repotted a bunch of plants and I think the bag must have had an infestation. All the new plants have gnats in and around them and they fly in my face when I am at my desk, in my sunroom, or at my bathroom vanity. 
 

I read on the internet (so it must be true) that you can spray a mixture of 1:4 hydrogen peroxide and water on the soil/plants. But I did this religiously for several days and it barely, if at all, made a difference. I stuck a bunch on my porch for a week or so but they still had gnats. 
 

This is driving me bonkers! If I can’t fix this problem in the next couple weeks, I’m going to dump all the newly potted plants and just get rid of the source. That would be a serious shame though, 

[Innisfree]

Sounds like fungus gnats.

https://www.thespruce.com/control-gnats-in-plants-4174817

https://www.gardeners.com/how-to/fungus-gnat/7317.html?SC=GGLNON&gclid=CjwKCAjw7diEBhB-EiwAskVi1-6_vgJytTau-3fFKpYFjXAGMv4H2PxHZKqV7W0neFTrleuqX1mIghoCGlQQAvD_BwE

 There are various soil drenches you can use, or you could try the methods in the links above. Just making sure the soil isn't too damp is a start.

[Arcadia]

I have tried vinegar for my kitchen countertop houseplants and it did trap a lot. My husband had used the UV bug zapper both indoors and outdoors. Our bug zapper looks similar to this https://www.amazon.com/gp/aw/d/B0861295JF/

https://homeguides.sfgate.com/safest-pesticide-use-plants-kill-gnats-100322.html

”Trapping

Trapping adult gnats is an effective method to get rid of existing populations while you treat the affected plants and soil, as not all the gnats will be on the plants or in the soil at any given time. Trap gnats by pouring an inch or so of apple cider vinegar into a disposable cup, then covering it with plastic wrap held in place with a rubber band. Small holes poked into the plastic wrap with a toothpick allow the gnats to enter the trap by climbing in, but they won't be able to fly back out. Leave the trap out overnight each night until no more gnats are caught.”

[eagleynne]

Assuming these are fungus gnats, which match your description, then I feel your pain. We had a major infestation here a few years ago after re-potting a bunch of plants. What we did was go buy a bunch of mosquito bits and sprinkle them up onto the soil around each plant. Then you lightly water the plant. Repeat the whole procedure every week until the problem is resolved. Mosquito bits contain Bacillus thuringiensis subspecies Israelensis which is fatal to the larvae of the gnats and mosquitos, but not dangerous for anything else. It can take a few weeks to see a lot of improvement since you have to wait for the current generation to die off before seeing a noticeable reduction in numbers, but it cleared up our really bad problem in a month.    

[kbutton]

Yellow sticky traps, new soil (I have taken to baking my soil because I've gotten bugs so many times when repotting), and spraying the surface of the dirt and the entire plant with high alcohol content rubbing alcohol. It dissipates very quickly, and it get into all the nooks and crannies. I spray all my new plants for a while when they enter the house if I don't have room to keep them separate.

I have also stopped putting my houseplants outdoors. They ALWAYS come back in with unwanted friends.

The last time this happened, it was so extensive that I ended up washing all my plant roots. My grandmother always swore by putting submerging her pots in soapy dishwater, but I found that my plants end up rotting. Most of the soapy insecticides build up in the soil to a level that the plants won't tolerate. So, I depotted mine, submerged them in water, washed pots, and repotted. Most tolerated this treatment, and it was effective--the remaining few bugs gravitated toward the sticky traps or were foiled by the alcohol. A few tender plants didn't make it, but I lost fewer plants than when I don't repot or wash roots.

[kbutton]

1 minute ago, eagleynne said:

Assuming these are fungus gnats, which match your description, then I feel your pain. We had a major infestation here a few years ago after re-potting a bunch of plants. What we did was go buy a bunch of mosquito bits and sprinkle them up onto the soil around each plant. Then you lightly water the plant. Repeat the whole procedure every week until the problem is resolved. Mosquito bits contain Bacillus thuringiensis subspecies Israelensis which is fatal to the larvae of the gnats and mosquitos, but not dangerous for anything else. It can take a few weeks to see a lot of improvement since you have to wait for the current generation to die off before seeing a noticeable reduction in numbers, but it cleared up our really bad problem in a month.    

That sound promising and like a lot less work than my methods! 

[Guest]

7 minutes ago, kbutton said:

That sound promising and like a lot less work than my methods! 

Still, I appreciate any ideas!

[Lori D.]

Not entirely environmentally friendly, but I just took plastic wrap and covered the soil so that only the plant stem came out of the plastic wrap, with the plastic wrap held in place against the soil with some small stones from the backyard. I only lifted the plastic wrap briefly to water once a week. After a month or two, it seems like the gnats had all died off and I could remove the stones and plastic wrap.

[Wildcat]

As @kbutton said upthread, you need to buy these --> https://www.amazon.com/Garsum-Sticky-Houseplant-Yellow-Insect/dp/B085GCX9H6/ref=sr_1_5?crid=214VNTXL0LXOJ&dchild=1&keywords=garsum+sticky+houseplant+traps+gnat+yellow+insect&qid=1620492317&sprefix=garsum+sticky+houseplant+traps+gnat+yellow+insect%2Caps%2C189&sr=8-5   They are fabulous.

I used them a few years ago in several plants that had a gnat outbreak of unknown origin that lasted all summer. These things catch all sorts of flying pests including fruit flies, sink gnats, and an occasional mosquito. At one point, long after the gnat war was over, I plopped one of these in a Dixie Cup sitting near my sink (with wadded paper inside to help hold up the stick) when we had sink gnats. They look gross with the little bodies on them, but you know they are working. 

Word to the wise, though.... these things are VERY sticky, so use your fingernails using the edges to carefully put them on their little sticks. Think Super Glue but gooey.

[BeachGal]

Here’s what I do: Mix 4 tablespoons of mosquito bits into 1 gallon of water. Place in dark spot for 6 hours. Skim off bits. Thoroughly drench affected plants and allow time for them to drain. This will kill the larvae in the soil but you might need to do multiple drenches. Allow plants to go as long as possible between drenches.

Depending on pot size, place multiple yellow sticky bug catchers in soil. Newly-emerged adults crawl on soil first and then fly. They no longer eat at this stage but are mating. You want to catch as many adults as possible because just one can lay many eggs.

I have a little fiddle leaf fig that lost most of its roots to fungus gnats. He’s bouncing back but it took quite a few drenchings and then rooting compound.

Edited May 8, 2021 by BeachGal

[Tree Frog]

2 hours ago, BeachGal said:

Here’s what I do: Mix 4 tablespoons of mosquito bits into 1 gallon of water. Place in dark spot for 6 hours. Skim off bits. Thoroughly drench affected plants and allow time for them to drain. This will kill the larvae in the soil but you might need to do multiple drenches. Allow plants to go as long as possible between drenches.

Depending on pot size, place multiple yellow sticky bug catchers in soil. Newly-emerged adults crawl on soil first and then fly. They no longer eat at this stage but are mating. You want to catch as many adults as possible because just one can lay many eggs.

I have a little fiddle leaf fig that lost most of its roots to fungus gnats. He’s bouncing back but it took quite a few drenchings and then rooting compound.

This is what I tried this morning. I've been putting mosquito bits on my soil and watering it in for several years, but this year, for whatever reason, it's no longer effective. I've been allowing my plants to dry out between waterings, but that's not helping, either. I'm on several local fb plant groups and it seems everyone is having this problem.

BeachGal, do you know how often the mosquito bits can be soaked? Do I need to remove them each time because they lose their effectiveness or can I add more water to them and reuse them?

 

[eagleynne]

38 minutes ago, wilrunner said:

This is what I tried this morning. I've been putting mosquito bits on my soil and watering it in for several years, but this year, for whatever reason, it's no longer effective. I've been allowing my plants to dry out between waterings, but that's not helping, either. I'm on several local fb plant groups and it seems everyone is having this problem.

BeachGal, do you know how often the mosquito bits can be soaked? Do I need to remove them each time because they lose their effectiveness or can I add more water to them and reuse them?

 

Not BeachGal, but it's my understanding that the bits themselves are just there to carry the bacteria that actually do the killing. So I would think that you might be able to reuse them once but that after that you would need new ones. We never reused them, we just scraped up any accumulated bits before adding new to the pot.

[Selkie]

Haven't had this problem myself, but people in my houseplant groups have successfully gotten rid of gnats by sprinkling cinnamon on top of the soil and only watering from the bottom.

[KungFuPanda]

I think you have to do the peroxide spray as a preventative.  I always spray my houseplants before bringing them back inside each fall. Once the gnats have hatched and are flying around they don't HAVE to hang out on the plants so spraying won't help much at that point..  Is it warm enough where you are to send your plants outside for the season? You might be able to save your plants that way.  You'll still have to kill the gnats and it's probably similar to dealing with fruit flies at that point.

I follow this gardener because he's local to me.  I know he had a gnat issue at one point, so here is the video he made to deal with them:

 

[kbutton]

@KungFuPanda, his channel looks great!

 

[BeachGal]

On 5/8/2021 at 3:20 PM, wilrunner said:

This is what I tried this morning. I've been putting mosquito bits on my soil and watering it in for several years, but this year, for whatever reason, it's no longer effective. I've been allowing my plants to dry out between waterings, but that's not helping, either. I'm on several local fb plant groups and it seems everyone is having this problem.

BeachGal, do you know how often the mosquito bits can be soaked? Do I need to remove them each time because they lose their effectiveness or can I add more water to them and reuse them?

 

I use fresh mosquito bits whenever I drench my plants. It's 4 tablespoons of bits added to 1 gallon of water. Then allow the bits' magic to soak into the water for 6 hours in a darkish area. That's what I do. I have no idea if the 6 hours are necessary or the dark area but it is the only thing that has worked for me.

Also, in regard to the yellow sticky traps, put a lot of them in the pot, not just one or two. You want to catch as many of them as possible because their life above ground is all about fertility! Just one pregnant gnat can lay 100-150 eggs, usually near the stem of the plant, so make sure to have the sticky stuff in that area especially.